diff --git a/AGENTS.md b/AGENTS.md
index 465ebfc4d3..4408a02822 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -410,6 +410,39 @@ This is useful for iterating on a specific test without running the full suite.
 - **Dependencies**: Inspect module dependency graph in `deps.rs`
 - **File Watching**: Monitor file change events in `watcher.rs`
 
+#### OpenTelemetry Tracing
+
+Rewatch supports OpenTelemetry (OTEL) tracing for build and watch commands. To visualize traces locally, run a Jaeger all-in-one container:
+
+```bash
+docker run -d --name jaeger \
+  -p 4317:4317 -p 4318:4318 -p 16686:16686 \
+  jaegertracing/all-in-one
+```
+
+Then run rewatch with the OTLP endpoint set:
+
+```bash
+OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318 cargo run --manifest-path rewatch/Cargo.toml -- build
+```
+
+Open http://localhost:16686 to view traces in the Jaeger UI.
+
+Note: Use `tracing::debug!` (not `log::debug!`) for events you want to appear in OTEL traces — they use separate logging systems.
+
+##### Honored environment variables
+
+Rewatch follows the OTEL spec for configuration — no rewatch-specific knobs exist.
+
+| Variable | Purpose |
+|---|---|
+| `OTEL_EXPORTER_OTLP_ENDPOINT` | Base endpoint of the collector (e.g. `http://localhost:4318`). `/v1/traces` is appended for the trace exporter. Setting this (or `OTEL_EXPORTER_OTLP_TRACES_ENDPOINT`) is what enables telemetry — if neither is set, tracing is a no-op. |
+| `OTEL_EXPORTER_OTLP_TRACES_ENDPOINT` | Full trace endpoint used verbatim. Overrides the general endpoint for traces. |
+| `OTEL_EXPORTER_OTLP_HEADERS` | Extra headers on exporter requests (e.g. `authorization=Bearer xyz`). |
+| `OTEL_SERVICE_NAME` | Service name reported on spans. Defaults to `rewatch`. |
+| `OTEL_RESOURCE_ATTRIBUTES` | Comma-separated `key=value` pairs added as resource attributes (e.g. `deployment.environment=ci,host.name=$HOSTNAME`). |
+| `RUST_LOG` | Controls which span/event levels are captured (e.g. `RUST_LOG=info`, `RUST_LOG=rewatch=debug`). Defaults to `debug` when telemetry is enabled. |
+
 #### Running Rewatch Directly
 
 When running the rewatch binary directly (via `cargo run` or the compiled binary) during development, you need to set environment variables to point to the local compiler and runtime. Otherwise, rewatch will try to use the installed versions:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 314e08424e..863bd868ef 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -36,6 +36,7 @@
 #### :nail_care: Polish
 
 - Allow builds while watchers are running. https://github.com/rescript-lang/rescript/pull/8349
+- Build system: Add OpenTelemetry tracing support for cli commands.
 
 #### :house: Internal
 
diff --git a/rewatch/Cargo.lock b/rewatch/Cargo.lock
index 5ebb674c3f..2a16bdc86e 100644
--- a/rewatch/Cargo.lock
+++ b/rewatch/Cargo.lock
@@ -92,6 +92,29 @@ version = "0.7.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7c02d123df017efcdfbd739ef81735b36c5ba83ec3c59c80a9d7ecc718f92e50"
 
+[[package]]
+name = "async-trait"
+version = "0.1.89"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9035ad2d096bed7955a320ee7e2230574d28fd3c3a0f186cbea1ff3c7eed5dbb"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "atomic-waker"
+version = "1.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1505bd5d3d116872e7271a6d4e16d81d0c8570876c8de68093a09ac269d8aac0"
+
+[[package]]
+name = "base64"
+version = "0.22.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
+
 [[package]]
 name = "bitflags"
 version = "1.3.2"
@@ -117,12 +140,27 @@ dependencies = [
  "constant_time_eq",
 ]
 
+[[package]]
+name = "block2"
+version = "0.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cdeb9d870516001442e364c5220d3574d2da8dc765554b4a617230d33fa58ef5"
+dependencies = [
+ "objc2",
+]
+
 [[package]]
 name = "bumpalo"
 version = "3.19.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "46c5e41b57b8bba42a04676d81cb89e9ee8e859a1a66f80a5a72e1cb76b34d43"
 
+[[package]]
+name = "bytes"
+version = "1.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e748733b7cbc798e1434b6ac524f0c1ff2ab456fe201501e6497c8417a4fc33"
+
 [[package]]
 name = "cc"
 version = "1.2.28"
@@ -270,12 +308,36 @@ checksum = "d0a5c400df2834b80a4c3327b3aad3a4c4cd4de0629063962b03235697506a28"
 
 [[package]]
 name = "ctrlc"
-version = "3.4.7"
+version = "3.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "46f93780a459b7d656ef7f071fe699c4d3d2cb201c4b24d085b6ddc505276e73"
+checksum = "e0b1fab2ae45819af2d0731d60f2afe17227ebb1a1538a236da84c93e9a60162"
 dependencies = [
+ "dispatch2",
  "nix",
- "windows-sys 0.59.0",
+ "windows-sys 0.61.2",
+]
+
+[[package]]
+name = "dispatch2"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e0e367e4e7da84520dedcac1901e4da967309406d1e51017ae1abfb97adbd38"
+dependencies = [
+ "bitflags 2.9.1",
+ "block2",
+ "libc",
+ "objc2",
+]
+
+[[package]]
+name = "displaydoc"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "97369cbbc041bc366949bc74d34658d6cda5621039731c6310521892a3a20ae0"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
 ]
 
 [[package]]
@@ -310,7 +372,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "778e2ac28f6c47af28e4907f13ffd1e1ddbd400980a9abd7c8df189bf578a5ad"
 dependencies = [
  "libc",
- "windows-sys 0.59.0",
+ "windows-sys 0.60.2",
 ]
 
 [[package]]
@@ -331,6 +393,15 @@ dependencies = [
  "windows-sys 0.59.0",
 ]
 
+[[package]]
+name = "form_urlencoded"
+version = "1.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb4cb245038516f5f85277875cdaa4f7d2c9a0fa0468de06ed190163b1581fcf"
+dependencies = [
+ "percent-encoding",
+]
+
 [[package]]
 name = "fsevent-sys"
 version = "4.1.0"
@@ -459,12 +530,197 @@ version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fc0fef456e4baa96da950455cd02c081ca953b141298e41db3fc7e36b1da849c"
 
+[[package]]
+name = "http"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e3ba2a386d7f85a81f119ad7498ebe444d2e22c2af0b86b069416ace48b3311a"
+dependencies = [
+ "bytes",
+ "itoa",
+]
+
+[[package]]
+name = "http-body"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1efedce1fb8e6913f23e0c92de8e62cd5b772a67e7b3946df930a62566c93184"
+dependencies = [
+ "bytes",
+ "http",
+]
+
+[[package]]
+name = "http-body-util"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b021d93e26becf5dc7e1b75b1bed1fd93124b374ceb73f43d4d4eafec896a64a"
+dependencies = [
+ "bytes",
+ "futures-core",
+ "http",
+ "http-body",
+ "pin-project-lite",
+]
+
+[[package]]
+name = "httparse"
+version = "1.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6dbf3de79e51f3d586ab4cb9d5c3e2c14aa28ed23d180cf89b4df0454a69cc87"
+
 [[package]]
 name = "humantime"
 version = "2.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9b112acc8b3adf4b107a8ec20977da0273a8c386765a3ec0229bd500a1443f9f"
 
+[[package]]
+name = "hyper"
+version = "1.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2ab2d4f250c3d7b1c9fcdff1cece94ea4e2dfbec68614f7b87cb205f24ca9d11"
+dependencies = [
+ "atomic-waker",
+ "bytes",
+ "futures-channel",
+ "futures-core",
+ "http",
+ "http-body",
+ "httparse",
+ "itoa",
+ "pin-project-lite",
+ "pin-utils",
+ "smallvec",
+ "tokio",
+ "want",
+]
+
+[[package]]
+name = "hyper-util"
+version = "0.1.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "96547c2556ec9d12fb1578c4eaf448b04993e7fb79cbaad930a656880a6bdfa0"
+dependencies = [
+ "base64",
+ "bytes",
+ "futures-channel",
+ "futures-util",
+ "http",
+ "http-body",
+ "hyper",
+ "ipnet",
+ "libc",
+ "percent-encoding",
+ "pin-project-lite",
+ "socket2",
+ "tokio",
+ "tower-service",
+ "tracing",
+]
+
+[[package]]
+name = "icu_collections"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4c6b649701667bbe825c3b7e6388cb521c23d88644678e83c0c4d0a621a34b43"
+dependencies = [
+ "displaydoc",
+ "potential_utf",
+ "yoke",
+ "zerofrom",
+ "zerovec",
+]
+
+[[package]]
+name = "icu_locale_core"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "edba7861004dd3714265b4db54a3c390e880ab658fec5f7db895fae2046b5bb6"
+dependencies = [
+ "displaydoc",
+ "litemap",
+ "tinystr",
+ "writeable",
+ "zerovec",
+]
+
+[[package]]
+name = "icu_normalizer"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5f6c8828b67bf8908d82127b2054ea1b4427ff0230ee9141c54251934ab1b599"
+dependencies = [
+ "icu_collections",
+ "icu_normalizer_data",
+ "icu_properties",
+ "icu_provider",
+ "smallvec",
+ "zerovec",
+]
+
+[[package]]
+name = "icu_normalizer_data"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7aedcccd01fc5fe81e6b489c15b247b8b0690feb23304303a9e560f37efc560a"
+
+[[package]]
+name = "icu_properties"
+version = "2.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "020bfc02fe870ec3a66d93e677ccca0562506e5872c650f893269e08615d74ec"
+dependencies = [
+ "icu_collections",
+ "icu_locale_core",
+ "icu_properties_data",
+ "icu_provider",
+ "zerotrie",
+ "zerovec",
+]
+
+[[package]]
+name = "icu_properties_data"
+version = "2.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "616c294cf8d725c6afcd8f55abc17c56464ef6211f9ed59cccffe534129c77af"
+
+[[package]]
+name = "icu_provider"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85962cf0ce02e1e0a629cc34e7ca3e373ce20dda4c4d7294bbd0bf1fdb59e614"
+dependencies = [
+ "displaydoc",
+ "icu_locale_core",
+ "writeable",
+ "yoke",
+ "zerofrom",
+ "zerotrie",
+ "zerovec",
+]
+
+[[package]]
+name = "idna"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3b0875f23caa03898994f6ddc501886a45c7d3d62d04d2d90788d47be1b1e4de"
+dependencies = [
+ "idna_adapter",
+ "smallvec",
+ "utf8_iter",
+]
+
+[[package]]
+name = "idna_adapter"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3acae9609540aa318d1bc588455225fb2085b9ed0c4f6bd0d9d5bcd86f1a0344"
+dependencies = [
+ "icu_normalizer",
+ "icu_properties",
+]
+
 [[package]]
 name = "indicatif"
 version = "0.17.11"
@@ -498,6 +754,22 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "ipnet"
+version = "2.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "469fb0b9cefa57e3ef31275ee7cacb78f2fdca44e4765491884a2b119d4eb130"
+
+[[package]]
+name = "iri-string"
+version = "0.7.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c91338f0783edbd6195decb37bae672fd3b165faffb89bf7b9e6942f8b1a731a"
+dependencies = [
+ "memchr",
+ "serde",
+]
+
 [[package]]
 name = "is-terminal"
 version = "0.4.16"
@@ -515,6 +787,15 @@ version = "1.70.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7943c866cc5cd64cbc25b2e01621d07fa8eb2a1a23160ee81ce38704e97b8ecf"
 
+[[package]]
+name = "itertools"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b192c782037fadd9cfa75548310488aabdbf3d2da73885b31bd0abd03351285"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "itoa"
 version = "1.0.15"
@@ -551,11 +832,17 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "lazy_static"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
+
 [[package]]
 name = "libc"
-version = "0.2.174"
+version = "0.2.185"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1171693293099992e19cddea4e8b849964e9846f4acee11b3948bcc337be8776"
+checksum = "52ff2c0fe9bc6cb6b14a0592c2ff4fa9ceb83eea9db979b0487cd054946a2b8f"
 
 [[package]]
 name = "libredox"
@@ -574,12 +861,27 @@ version = "0.9.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cd945864f07fe9f5371a27ad7b52a172b4b499999f1d97574c9fa68373937e12"
 
+[[package]]
+name = "litemap"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6373607a59f0be73a39b6fe456b8192fcc3585f602af20751600e974dd455e77"
+
 [[package]]
 name = "log"
 version = "0.4.27"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "13dc2df351e3202783a1fe0d44375f7295ffb4049267b0f3018346dc122a1d94"
 
+[[package]]
+name = "matchers"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d1525a2a28c7f4fa0fc98bb91ae755d1e2d1505079e05539e35bc876b5d65ae9"
+dependencies = [
+ "regex-automata",
+]
+
 [[package]]
 name = "memchr"
 version = "2.7.5"
@@ -598,11 +900,22 @@ dependencies = [
  "windows-sys 0.48.0",
 ]
 
+[[package]]
+name = "mio"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "69d83b0086dc8ecf3ce9ae2874b2d1290252e2a30720bea58a5c6639b0092873"
+dependencies = [
+ "libc",
+ "wasi 0.11.1+wasi-snapshot-preview1",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "nix"
-version = "0.30.1"
+version = "0.31.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "74523f3a35e05aba87a1d978330aef40f67b0304ac79c1c00b294c9830543db6"
+checksum = "5d6d0705320c1e6ba1d912b5e37cf18071b6c2e9b7fa8215a1e8a7651966f5d3"
 dependencies = [
  "bitflags 2.9.1",
  "cfg-if",
@@ -623,7 +936,7 @@ dependencies = [
  "inotify",
  "kqueue",
  "libc",
- "mio",
+ "mio 0.8.11",
  "serde",
  "walkdir",
  "windows-sys 0.45.0",
@@ -638,6 +951,15 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "nu-ansi-term"
+version = "0.50.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7957b9740744892f114936ab4a57b3f487491bbeafaf8083688b16841a4240e5"
+dependencies = [
+ "windows-sys 0.60.2",
+]
+
 [[package]]
 name = "num_cpus"
 version = "1.17.0"
@@ -654,6 +976,21 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "830b246a0e5f20af87141b25c173cd1b609bd7779a4617d6ec582abaf90870f3"
 
+[[package]]
+name = "objc2"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3a12a8ed07aefc768292f076dc3ac8c48f3781c8f2d5851dd3d98950e8c5a89f"
+dependencies = [
+ "objc2-encode",
+]
+
+[[package]]
+name = "objc2-encode"
+version = "4.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ef25abbcd74fb2609453eb695bd2f860d389e457f67dc17cafc8b8cbc89d0c33"
+
 [[package]]
 name = "once_cell"
 version = "1.21.3"
@@ -667,91 +1004,258 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a4895175b425cb1f87721b59f0f286c2092bd4af812243672510e1ac53e2e0ad"
 
 [[package]]
-name = "pin-project-lite"
-version = "0.2.16"
+name = "opentelemetry"
+version = "0.31.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3b3cff922bd51709b605d9ead9aa71031d81447142d828eb4a6eba76fe619f9b"
+checksum = "b84bcd6ae87133e903af7ef497404dda70c60d0ea14895fc8a5e6722754fc2a0"
+dependencies = [
+ "futures-core",
+ "futures-sink",
+ "js-sys",
+ "pin-project-lite",
+ "thiserror",
+ "tracing",
+]
 
 [[package]]
-name = "pin-utils"
-version = "0.1.0"
+name = "opentelemetry-http"
+version = "0.31.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8b870d8c151b6f2fb93e84a13146138f05d02ed11c7e7c54f8826aaaf7c9f184"
+checksum = "d7a6d09a73194e6b66df7c8f1b680f156d916a1a942abf2de06823dd02b7855d"
+dependencies = [
+ "async-trait",
+ "bytes",
+ "http",
+ "opentelemetry",
+ "reqwest",
+]
 
 [[package]]
-name = "portable-atomic"
-version = "1.11.1"
+name = "opentelemetry-otlp"
+version = "0.31.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f84267b20a16ea918e43c6a88433c2d54fa145c92a811b5b047ccbe153674483"
+checksum = "1f69cd6acbb9af919df949cd1ec9e5e7fdc2ef15d234b6b795aaa525cc02f71f"
+dependencies = [
+ "http",
+ "opentelemetry",
+ "opentelemetry-http",
+ "opentelemetry-proto",
+ "opentelemetry_sdk",
+ "prost",
+ "reqwest",
+ "thiserror",
+]
 
 [[package]]
-name = "proc-macro2"
-version = "1.0.95"
+name = "opentelemetry-proto"
+version = "0.31.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
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+dependencies = [
+ "base64",
+ "bytes",
+ "futures-channel",
+ "futures-core",
+ "futures-util",
+ "http",
+ "http-body",
+ "http-body-util",
+ "hyper",
+ "hyper-util",
+ "js-sys",
+ "log",
+ "percent-encoding",
+ "pin-project-lite",
+ "serde",
+ "serde_json",
+ "serde_urlencoded",
+ "sync_wrapper",
+ "tokio",
+ "tower",
+ "tower-http",
+ "tower-service",
+ "url",
+ "wasm-bindgen",
+ "wasm-bindgen-futures",
+ "web-sys",
+]
+
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@@ -785,6 +1323,9 @@ dependencies = [
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  "notify",
  "num_cpus",
+ "opentelemetry",
+ "opentelemetry-otlp",
+ "opentelemetry_sdk",
  "rayon",
  "regex",
  "serde",
@@ -793,6 +1334,9 @@ dependencies = [
  "serde_path_to_error",
  "sysinfo",
  "tempfile",
+ "tracing",
+ "tracing-opentelemetry",
+ "tracing-subscriber",
 ]
 
 [[package]]
@@ -805,9 +1349,15 @@ dependencies = [
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  "libc",
  "linux-raw-sys",
- "windows-sys 0.59.0",
+ "windows-sys 0.60.2",
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+[[package]]
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+
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@@ -886,6 +1436,27 @@ dependencies = [
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+checksum = "d3491c14715ca2294c4d6a88f15e84739788c1d030eed8c110436aafdaa2f3fd"
+dependencies = [
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+ "itoa",
+ "ryu",
+ "serde",
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+dependencies = [
+ "lazy_static",
+]
+
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+
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+dependencies = [
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+ "windows-sys 0.60.2",
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+
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+
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@@ -915,6 +1508,26 @@ dependencies = [
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+checksum = "0bf256ce5efdfa370213c1dabab5935a12e49f2c58d15e9eac2870d3b4f27263"
+dependencies = [
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+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
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@@ -952,6 +1565,229 @@ dependencies = [
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+ "quote",
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+ "opentelemetry",
+ "smallvec",
+ "tracing",
+ "tracing-core",
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+dependencies = [
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+ "nu-ansi-term",
+ "once_cell",
+ "regex-automata",
+ "sharded-slab",
+ "smallvec",
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+
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 checksum = "4a1a07cc7db3810833284e8d372ccdc6da29741639ecc70c9ec107df0fa6154c"
 
+[[package]]
+name = "url"
+version = "2.5.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ff67a8a4397373c3ef660812acab3268222035010ab8680ec4215f38ba3d0eed"
+dependencies = [
+ "form_urlencoded",
+ "idna",
+ "percent-encoding",
+ "serde",
+]
+
+[[package]]
+name = "utf8_iter"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6c140620e7ffbb22c2dee59cafe6084a59b5ffc27a8859a5f0d494b5d52b6be"
+
 [[package]]
 name = "utf8parse"
 version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "06abde3611657adf66d383f00b093d7faecc7fa57071cce2578660c9f1010821"
 
+[[package]]
+name = "valuable"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba73ea9cf16a25df0c8caa16c51acb937d5712a8429db78a3ee29d5dcacd3a65"
+
 [[package]]
 name = "version_check"
 version = "0.9.5"
@@ -992,6 +1852,15 @@ dependencies = [
  "winapi-util",
 ]
 
+[[package]]
+name = "want"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bfa7760aed19e106de2c7c0b581b509f2f25d3dacaf737cb82ac61bc6d760b0e"
+dependencies = [
+ "try-lock",
+]
+
 [[package]]
 name = "wasi"
 version = "0.11.1+wasi-snapshot-preview1"
@@ -1015,6 +1884,7 @@ checksum = "1edc8929d7499fc4e8f0be2262a241556cfc54a0bea223790e71446f2aab1ef5"
 dependencies = [
  "cfg-if",
  "once_cell",
+ "rustversion",
  "wasm-bindgen-macro",
 ]
 
@@ -1032,6 +1902,19 @@ dependencies = [
  "wasm-bindgen-shared",
 ]
 
+[[package]]
+name = "wasm-bindgen-futures"
+version = "0.4.50"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "555d470ec0bc3bb57890405e5d4322cc9ea83cebb085523ced7be4144dac1e61"
+dependencies = [
+ "cfg-if",
+ "js-sys",
+ "once_cell",
+ "wasm-bindgen",
+ "web-sys",
+]
+
 [[package]]
 name = "wasm-bindgen-macro"
 version = "0.2.100"
@@ -1064,6 +1947,16 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "web-sys"
+version = "0.3.77"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "33b6dd2ef9186f1f2072e409e99cd22a975331a6b3591b12c764e0e55c60d5d2"
+dependencies = [
+ "js-sys",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "web-time"
 version = "1.1.0"
@@ -1096,7 +1989,7 @@ version = "0.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf221c93e13a30d793f7645a0e7762c55d169dbb0a49671918a2319d289b10bb"
 dependencies = [
- "windows-sys 0.59.0",
+ "windows-sys 0.48.0",
 ]
 
 [[package]]
@@ -1105,6 +1998,12 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 
+[[package]]
+name = "windows-link"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
+
 [[package]]
 name = "windows-sys"
 version = "0.45.0"
@@ -1132,6 +2031,24 @@ dependencies = [
  "windows-targets 0.52.6",
 ]
 
+[[package]]
+name = "windows-sys"
+version = "0.60.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f2f500e4d28234f72040990ec9d39e3a6b950f9f22d3dba18416c35882612bcb"
+dependencies = [
+ "windows-targets 0.53.5",
+]
+
+[[package]]
+name = "windows-sys"
+version = "0.61.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
+dependencies = [
+ "windows-link",
+]
+
 [[package]]
 name = "windows-targets"
 version = "0.42.2"
@@ -1171,13 +2088,30 @@ dependencies = [
  "windows_aarch64_gnullvm 0.52.6",
  "windows_aarch64_msvc 0.52.6",
  "windows_i686_gnu 0.52.6",
- "windows_i686_gnullvm",
+ "windows_i686_gnullvm 0.52.6",
  "windows_i686_msvc 0.52.6",
  "windows_x86_64_gnu 0.52.6",
  "windows_x86_64_gnullvm 0.52.6",
  "windows_x86_64_msvc 0.52.6",
 ]
 
+[[package]]
+name = "windows-targets"
+version = "0.53.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4945f9f551b88e0d65f3db0bc25c33b8acea4d9e41163edf90dcd0b19f9069f3"
+dependencies = [
+ "windows-link",
+ "windows_aarch64_gnullvm 0.53.1",
+ "windows_aarch64_msvc 0.53.1",
+ "windows_i686_gnu 0.53.1",
+ "windows_i686_gnullvm 0.53.1",
+ "windows_i686_msvc 0.53.1",
+ "windows_x86_64_gnu 0.53.1",
+ "windows_x86_64_gnullvm 0.53.1",
+ "windows_x86_64_msvc 0.53.1",
+]
+
 [[package]]
 name = "windows_aarch64_gnullvm"
 version = "0.42.2"
@@ -1196,6 +2130,12 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "32a4622180e7a0ec044bb555404c800bc9fd9ec262ec147edd5989ccd0c02cd3"
 
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a9d8416fa8b42f5c947f8482c43e7d89e73a173cead56d044f6a56104a6d1b53"
+
 [[package]]
 name = "windows_aarch64_msvc"
 version = "0.42.2"
@@ -1214,6 +2154,12 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "09ec2a7bb152e2252b53fa7803150007879548bc709c039df7627cabbd05d469"
 
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b9d782e804c2f632e395708e99a94275910eb9100b2114651e04744e9b125006"
+
 [[package]]
 name = "windows_i686_gnu"
 version = "0.42.2"
@@ -1232,12 +2178,24 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8e9b5ad5ab802e97eb8e295ac6720e509ee4c243f69d781394014ebfe8bbfa0b"
 
+[[package]]
+name = "windows_i686_gnu"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "960e6da069d81e09becb0ca57a65220ddff016ff2d6af6a223cf372a506593a3"
+
 [[package]]
 name = "windows_i686_gnullvm"
 version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0eee52d38c090b3caa76c563b86c3a4bd71ef1a819287c19d586d7334ae8ed66"
 
+[[package]]
+name = "windows_i686_gnullvm"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fa7359d10048f68ab8b09fa71c3daccfb0e9b559aed648a8f95469c27057180c"
+
 [[package]]
 name = "windows_i686_msvc"
 version = "0.42.2"
@@ -1256,6 +2214,12 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "240948bc05c5e7c6dabba28bf89d89ffce3e303022809e73deaefe4f6ec56c66"
 
+[[package]]
+name = "windows_i686_msvc"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e7ac75179f18232fe9c285163565a57ef8d3c89254a30685b57d83a38d326c2"
+
 [[package]]
 name = "windows_x86_64_gnu"
 version = "0.42.2"
@@ -1274,6 +2238,12 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "147a5c80aabfbf0c7d901cb5895d1de30ef2907eb21fbbab29ca94c5b08b1a78"
 
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c3842cdd74a865a8066ab39c8a7a473c0778a3f29370b5fd6b4b9aa7df4a499"
+
 [[package]]
 name = "windows_x86_64_gnullvm"
 version = "0.42.2"
@@ -1292,6 +2262,12 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "24d5b23dc417412679681396f2b49f3de8c1473deb516bd34410872eff51ed0d"
 
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ffa179e2d07eee8ad8f57493436566c7cc30ac536a3379fdf008f47f6bb7ae1"
+
 [[package]]
 name = "windows_x86_64_msvc"
 version = "0.42.2"
@@ -1310,6 +2286,12 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec"
 
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.53.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d6bbff5f0aada427a1e5a6da5f1f98158182f26556f345ac9e04d36d0ebed650"
+
 [[package]]
 name = "wit-bindgen-rt"
 version = "0.39.0"
@@ -1319,6 +2301,35 @@ dependencies = [
  "bitflags 2.9.1",
 ]
 
+[[package]]
+name = "writeable"
+version = "0.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9edde0db4769d2dc68579893f2306b26c6ecfbe0ef499b013d731b7b9247e0b9"
+
+[[package]]
+name = "yoke"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72d6e5c6afb84d73944e5cedb052c4680d5657337201555f9f2a16b7406d4954"
+dependencies = [
+ "stable_deref_trait",
+ "yoke-derive",
+ "zerofrom",
+]
+
+[[package]]
+name = "yoke-derive"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b659052874eb698efe5b9e8cf382204678a0086ebf46982b79d6ca3182927e5d"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+ "synstructure",
+]
+
 [[package]]
 name = "zerocopy"
 version = "0.8.26"
@@ -1338,3 +2349,57 @@ dependencies = [
  "quote",
  "syn",
 ]
+
+[[package]]
+name = "zerofrom"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "50cc42e0333e05660c3587f3bf9d0478688e15d870fab3346451ce7f8c9fbea5"
+dependencies = [
+ "zerofrom-derive",
+]
+
+[[package]]
+name = "zerofrom-derive"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d71e5d6e06ab090c67b5e44993ec16b72dcbaabc526db883a360057678b48502"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+ "synstructure",
+]
+
+[[package]]
+name = "zerotrie"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2a59c17a5562d507e4b54960e8569ebee33bee890c70aa3fe7b97e85a9fd7851"
+dependencies = [
+ "displaydoc",
+ "yoke",
+ "zerofrom",
+]
+
+[[package]]
+name = "zerovec"
+version = "0.11.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c28719294829477f525be0186d13efa9a3c602f7ec202ca9e353d310fb9a002"
+dependencies = [
+ "yoke",
+ "zerofrom",
+ "zerovec-derive",
+]
+
+[[package]]
+name = "zerovec-derive"
+version = "0.11.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eadce39539ca5cb3985590102671f2567e659fca9666581ad3411d59207951f3"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
diff --git a/rewatch/Cargo.toml b/rewatch/Cargo.toml
index e80f10b40f..15a555a85f 100644
--- a/rewatch/Cargo.toml
+++ b/rewatch/Cargo.toml
@@ -12,7 +12,12 @@ clap = { version = "4.3", features = ["derive"] }
 clap-verbosity-flag = "2.2"
 console = "0.15.5"
 convert_case = "0.6.0"
-ctrlc = "3.4.4"
+# The "termination" feature extends ctrlc's handler to also catch SIGTERM and
+# SIGHUP (not just SIGINT). This is required so the telemetry guard's Drop
+# runs on those signals and buffered OTLP spans get flushed before exit.
+# Without it, `kill <pid>` or a container/systemd stop would silently drop
+# the last batch of traces.
+ctrlc = { version = "3.4.4", features = ["termination"] }
 env_logger = "0.10"
 futures = "0.3.25"
 futures-timer = "3.0.2"
@@ -29,6 +34,20 @@ serde_path_to_error = "0.1.16"
 sysinfo = "0.29.10"
 tempfile = "3.10.1"
 
+# OpenTelemetry for tracing
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+tracing-opentelemetry = "0.32"
+opentelemetry = "0.31"
+opentelemetry_sdk = "0.31"
+# default-features disabled to skip metrics/logs support and the internal-logs
+# feature we don't need. We only use HTTP/protobuf trace export via blocking
+# reqwest — no Tokio runtime required.
+opentelemetry-otlp = { version = "0.31", default-features = false, features = [
+    "http-proto",
+    "reqwest-blocking-client",
+    "trace",
+] }
 
 [profile.release]
 codegen-units = 1
diff --git a/rewatch/src/build.rs b/rewatch/src/build.rs
index 88394eddda..66ea61743f 100644
--- a/rewatch/src/build.rs
+++ b/rewatch/src/build.rs
@@ -28,6 +28,7 @@ use std::fs::File;
 use std::io::Write;
 use std::path::{Path, PathBuf};
 use std::time::{Duration, Instant};
+use tracing::{info_span, instrument};
 
 fn is_dirty(module: &Module) -> bool {
     match module.source_type {
@@ -56,6 +57,7 @@ pub struct CompilerArgs {
     pub parser_args: Vec<String>,
 }
 
+#[instrument(name = "rewatch.compiler_args", skip_all, fields(file_path = %rescript_file_path.display()))]
 pub fn get_compiler_args(rescript_file_path: &Path) -> Result<String> {
     let filename = &helpers::get_abs_path(rescript_file_path);
     let current_package = helpers::get_abs_path(
@@ -127,6 +129,7 @@ pub fn get_compiler_info(project_context: &ProjectContext) -> Result<CompilerInf
     })
 }
 
+#[instrument(name = "build.initialize", skip_all)]
 pub fn initialize_build(
     default_timing: Option<Duration>,
     filter: &Option<regex::Regex>,
@@ -237,6 +240,7 @@ impl fmt::Display for IncrementalBuildError {
     }
 }
 
+#[instrument(name = "build.incremental", skip_all, fields(module_count = build_state.modules.len()))]
 pub fn incremental_build(
     build_state: &mut BuildCommandState,
     default_timing: Option<Duration>,
@@ -279,6 +283,7 @@ pub fn incremental_build(
             warnings
         }
         Err(err) => {
+            let _error_span = info_span!("build.parse_error").entered();
             logs::finalize(&build_state.packages);
 
             if !plain_output && show_progress {
@@ -374,6 +379,7 @@ pub fn incremental_build(
     }
     pb.finish();
     if !compile_errors.is_empty() {
+        let _error_span = info_span!("build.compile_error").entered();
         if show_progress {
             if plain_output {
                 eprintln!("Compiled {num_compiled_modules} modules")
@@ -389,6 +395,7 @@ pub fn incremental_build(
             }
         }
         if helpers::contains_ascii_characters(&compile_warnings) {
+            let _warning_span = info_span!("build.compile_warning").entered();
             eprintln!("{}", &compile_warnings);
         }
         if initial_build {
@@ -482,6 +489,7 @@ pub fn write_build_ninja(build_state: &BuildCommandState) {
 }
 
 #[allow(clippy::too_many_arguments)]
+#[instrument(name = "rewatch.build", skip_all, fields(working_dir = %path.display()))]
 pub fn build(
     filter: &Option<regex::Regex>,
     path: &Path,
diff --git a/rewatch/src/build/clean.rs b/rewatch/src/build/clean.rs
index 73e77987dd..2ecc4de32f 100644
--- a/rewatch/src/build/clean.rs
+++ b/rewatch/src/build/clean.rs
@@ -13,6 +13,7 @@ use rayon::prelude::*;
 use std::io::Write;
 use std::path::{Path, PathBuf};
 use std::time::Instant;
+use tracing::instrument;
 
 fn remove_ast(package: &packages::Package, source_file: &Path) {
     let _ = std::fs::remove_file(helpers::get_compiler_asset(
@@ -102,6 +103,7 @@ fn clean_source_files(build_state: &BuildState, root_config: &Config) {
 // TODO: change to scan_previous_build => CompileAssetsState
 // and then do cleanup on that state (for instance remove all .mjs files that are not in the state)
 
+#[instrument(name = "clean.cleanup_previous_build", skip_all)]
 pub fn cleanup_previous_build(
     build_state: &mut BuildCommandState,
     compile_assets_state: CompileAssetsState,
@@ -332,6 +334,7 @@ pub fn cleanup_after_build(build_state: &BuildCommandState) {
     });
 }
 
+#[instrument(name = "rewatch.clean", skip_all, fields(working_dir = %path.display()))]
 pub fn clean(path: &Path, show_progress: bool, plain_output: bool, prod: bool) -> Result<()> {
     let project_context = ProjectContext::new(path)?;
     let compiler_info = build::get_compiler_info(&project_context)?;
diff --git a/rewatch/src/build/compile.rs b/rewatch/src/build/compile.rs
index 5247342a2a..2a7ceb849c 100644
--- a/rewatch/src/build/compile.rs
+++ b/rewatch/src/build/compile.rs
@@ -20,6 +20,7 @@ use std::path::PathBuf;
 use std::process::Command;
 use std::sync::OnceLock;
 use std::time::SystemTime;
+use tracing::{info_span, instrument};
 
 /// Execute js-post-build command for a compiled JavaScript file.
 /// The command runs in the directory containing the rescript.json that defines it.
@@ -27,6 +28,13 @@ use std::time::SystemTime;
 fn execute_post_build_command(cmd: &str, js_file_path: &Path, working_dir: &Path) -> Result<()> {
     let full_command = format!("{} {}", cmd, js_file_path.display());
 
+    let _span = info_span!(
+        "build.js_post_build",
+        command = %cmd,
+        js_file = %js_file_path.display(),
+    )
+    .entered();
+
     debug!(
         "Executing js-post-build: {} (in {})",
         full_command,
@@ -72,6 +80,7 @@ fn execute_post_build_command(cmd: &str, js_file_path: &Path, working_dir: &Path
     }
 }
 
+#[instrument(name = "build.compile", skip_all)]
 pub fn compile(
     build_state: &mut BuildCommandState,
     show_progress: bool,
@@ -162,6 +171,13 @@ pub fn compile(
             loop_count,
         );
 
+        let wave_span = info_span!(
+            "build.compile_wave",
+            wave = loop_count,
+            file_count = in_progress_modules.len(),
+        );
+        let _wave_entered = wave_span.enter();
+
         let current_in_progres_modules = in_progress_modules.clone();
 
         let results = current_in_progres_modules
@@ -196,6 +212,31 @@ pub fn compile(
                             ))
                         }
                         SourceType::SourceFile(source_file) => {
+                            // Construct span + attributes only when a subscriber is listening.
+                            // Otherwise root_config.get_package_specs() (which clones) and the
+                            // attribute formatting run per-module on the build hot path.
+                            let _file_span = if tracing::enabled!(tracing::Level::INFO) {
+                                let root_config = build_state.get_root_config();
+                                let specs = root_config.get_package_specs();
+                                // A package can be built under multiple specs (e.g. ESM + CJS).
+                                // Report all of them joined by "," instead of silently picking
+                                // the first — the compile_file span covers work for every spec.
+                                let suffix = specs
+                                    .iter()
+                                    .map(|s| root_config.get_suffix(s))
+                                    .collect::<Vec<_>>()
+                                    .join(",");
+                                let module_system = specs
+                                    .iter()
+                                    .map(|s| s.module.as_str())
+                                    .collect::<Vec<_>>()
+                                    .join(",");
+                                let namespace = package.namespace.to_suffix().unwrap_or_default();
+                                info_span!(parent: &wave_span, "build.compile_file", module = %module_name, package = %package.name, suffix, module_system, namespace).entered()
+                            } else {
+                                tracing::Span::none().entered()
+                            };
+
                             let cmi_path = helpers::get_compiler_asset(
                                 package,
                                 &package.namespace,
diff --git a/rewatch/src/build/packages.rs b/rewatch/src/build/packages.rs
index a936b415f6..1754fa9d0f 100644
--- a/rewatch/src/build/packages.rs
+++ b/rewatch/src/build/packages.rs
@@ -18,6 +18,7 @@ use std::fs::{self};
 use std::hash::{Hash, Hasher};
 use std::path::{Path, PathBuf};
 use std::time::SystemTime;
+use tracing::{info_span, instrument};
 
 #[derive(Debug, Clone)]
 pub struct SourceFileMeta {
@@ -607,6 +608,7 @@ fn extend_with_children(
     prod: bool,
 ) -> AHashMap<String, Package> {
     for (_key, package) in build.iter_mut() {
+        let _span = info_span!("build.load_package_sources", package = %package.name).entered();
         let mut map: AHashMap<PathBuf, SourceFileMeta> = AHashMap::new();
         package
             .source_folders
@@ -656,6 +658,7 @@ fn extend_with_children(
 ///    interface files.
 ///
 /// The two step process is there to reduce IO overhead.
+#[instrument(name = "packages.make", skip_all)]
 pub fn make(
     filter: &Option<regex::Regex>,
     project_context: &ProjectContext,
@@ -671,6 +674,7 @@ pub fn make(
     Ok(result)
 }
 
+#[instrument(name = "packages.parse_packages", skip_all)]
 pub fn parse_packages(build_state: &mut BuildState) -> Result<()> {
     let packages = build_state.packages.clone();
     for (package_name, package) in packages.iter() {
diff --git a/rewatch/src/build/parse.rs b/rewatch/src/build/parse.rs
index 223d49d90e..0945f30d35 100644
--- a/rewatch/src/build/parse.rs
+++ b/rewatch/src/build/parse.rs
@@ -12,6 +12,7 @@ use log::debug;
 use rayon::prelude::*;
 use std::path::{Path, PathBuf};
 use std::process::Command;
+use tracing::info_span;
 
 pub fn generate_asts(
     build_state: &mut BuildCommandState,
@@ -20,6 +21,26 @@ pub fn generate_asts(
     let mut has_failure = false;
     let mut stderr = "".to_string();
 
+    // Count dirty modules for the span attribute only when a subscriber is
+    // listening. Otherwise iterating every module every parse phase is pure
+    // waste on the hot path.
+    let parse_span = if tracing::enabled!(tracing::Level::INFO) {
+        let dirty_modules = build_state
+            .modules
+            .values()
+            .filter(|m| match &m.source_type {
+                SourceType::SourceFile(sf) => {
+                    sf.implementation.parse_dirty || sf.interface.as_ref().is_some_and(|i| i.parse_dirty)
+                }
+                SourceType::MlMap(mlmap) => mlmap.parse_dirty,
+            })
+            .count();
+        info_span!("build.parse", dirty_modules = dirty_modules)
+    } else {
+        tracing::Span::none()
+    };
+    let _span = parse_span.enter();
+
     build_state
         .modules
         .par_iter()
@@ -53,6 +74,7 @@ pub fn generate_asts(
                             &source_file.implementation.path.to_owned(),
                             build_state,
                             build_state.get_warn_error_override(),
+                            &parse_span,
                         )
                         .map_err(|e| e.to_string());
 
@@ -63,6 +85,7 @@ pub fn generate_asts(
                                     &interface_file_path.to_owned(),
                                     build_state,
                                     build_state.get_warn_error_override(),
+                                    &parse_span,
                                 ) {
                                     Ok(v) => Ok(Some(v)),
                                     Err(e) => Err(e.to_string()),
@@ -322,11 +345,52 @@ pub fn parser_args(
     ))
 }
 
+fn make_parse_file_span(
+    filename: &Path,
+    package: &Package,
+    parser_args: &[String],
+    build_state: &BuildState,
+    parent: &tracing::Span,
+) -> tracing::Span {
+    let module_name = helpers::file_path_to_module_name(filename, &package.namespace);
+    let mut ppx_names: Vec<String> = Vec::new();
+    let mut experimental: Vec<String> = Vec::new();
+    for pair in parser_args.windows(2) {
+        if pair[0] == "-ppx" {
+            // Use the PPX executable's file name so paths like
+            // `node_modules/foo/ppx.exe` reduce to `ppx.exe` cross-platform.
+            let name = Path::new(&pair[1])
+                .file_name()
+                .map(|s| s.to_string_lossy().into_owned())
+                .unwrap_or_else(|| pair[1].clone());
+            ppx_names.push(name);
+        } else if pair[0] == "-enable-experimental" {
+            experimental.push(pair[1].clone());
+        }
+    }
+    let ppx = ppx_names.join(",");
+    let experimental = experimental.join(",");
+    let root_config = build_state.get_root_config();
+    let jsx = root_config.get_jsx_args().get(1).cloned().unwrap_or_default();
+    let bsc_flags = config::flatten_flags(&package.config.compiler_flags).join(" ");
+    info_span!(
+        parent: parent,
+        "build.parse_file",
+        module = %module_name,
+        package = %package.name,
+        ppx = %ppx,
+        experimental = %experimental,
+        jsx = %jsx,
+        bsc_flags = %bsc_flags,
+    )
+}
+
 fn generate_ast(
     package: Package,
     filename: &Path,
     build_state: &BuildState,
     warn_error_override: Option<String>,
+    parent_span: &tracing::Span,
 ) -> anyhow::Result<(PathBuf, Option<helpers::StdErr>)> {
     let file_path = PathBuf::from(&package.path).join(filename);
     let contents = helpers::read_file(&file_path).expect("Error reading file");
@@ -341,6 +405,12 @@ fn generate_ast(
         warn_error_override,
     )?;
 
+    let _parse_span = if tracing::enabled!(tracing::Level::INFO) {
+        make_parse_file_span(filename, &package, &parser_args, build_state, parent_span).entered()
+    } else {
+        tracing::Span::none().entered()
+    };
+
     // generate the dir of the ast_path (it mirrors the source file dir)
     let ast_parent_path = package.get_build_path().join(ast_path.parent().unwrap());
     helpers::create_path(&ast_parent_path);
diff --git a/rewatch/src/cli.rs b/rewatch/src/cli.rs
index 07c3cdfb9b..60b4ebffe7 100644
--- a/rewatch/src/cli.rs
+++ b/rewatch/src/cli.rs
@@ -11,7 +11,7 @@
 //
 // However, we may want to revisit the decision to use clap after the v12 release.
 
-use std::{env, ffi::OsString, ops::Deref};
+use std::{env, ffi::OsString, ops::Deref, path::Path};
 
 use clap::{Args, CommandFactory, Parser, Subcommand, error::ErrorKind};
 use clap_verbosity_flag::InfoLevel;
@@ -496,6 +496,12 @@ impl Deref for FolderArg {
     }
 }
 
+impl AsRef<Path> for FolderArg {
+    fn as_ref(&self) -> &Path {
+        Path::new(&self.folder)
+    }
+}
+
 impl Deref for FilterArg {
     type Target = Option<Regex>;
 
diff --git a/rewatch/src/format.rs b/rewatch/src/format.rs
index c4ea876e45..1c70d95987 100644
--- a/rewatch/src/format.rs
+++ b/rewatch/src/format.rs
@@ -7,11 +7,13 @@ use std::io::{self, Write};
 use std::path::Path;
 use std::process::Command;
 use std::sync::atomic::{AtomicUsize, Ordering};
+use tracing::{info_span, instrument};
 
 use crate::build::packages;
 use crate::cli::FileExtension;
 use clap::ValueEnum;
 
+#[instrument(name = "rewatch.format", skip_all, fields(check, is_stdin = stdin_extension.is_some()))]
 pub fn format(stdin_extension: Option<FileExtension>, check: bool, files: Vec<String>) -> Result<()> {
     let bsc_path = helpers::get_bsc();
 
@@ -102,6 +104,7 @@ fn format_files(bsc_exe: &Path, files: Vec<String>, check: bool) -> Result<()> {
                         eprintln!("[format check] {file}");
                         incorrectly_formatted_files.fetch_add(1, Ordering::SeqCst);
                     } else {
+                        let _file_span = info_span!("format.write_file", file = %file).entered();
                         // Only write if content actually changed
                         fs::write(file, &*formatted_content)?;
                     }
diff --git a/rewatch/src/lib.rs b/rewatch/src/lib.rs
index a389e8172e..2216c16fa8 100644
--- a/rewatch/src/lib.rs
+++ b/rewatch/src/lib.rs
@@ -8,4 +8,5 @@ pub mod lock;
 pub mod project_context;
 pub mod queue;
 pub mod sourcedirs;
+pub mod telemetry;
 pub mod watcher;
diff --git a/rewatch/src/main.rs b/rewatch/src/main.rs
index 9d3a235435..9bafc60533 100644
--- a/rewatch/src/main.rs
+++ b/rewatch/src/main.rs
@@ -6,32 +6,50 @@ use std::{io::Write, path::Path};
 use rescript::{
     build, cli, cmd, format,
     lock::{LockKind, drop_lock, get_lock_or_exit},
-    watcher,
+    telemetry, watcher,
 };
 
-fn main() -> Result<()> {
+fn main() {
+    // Initialize telemetry (only active if OTEL_EXPORTER_OTLP_ENDPOINT is set)
+    let telemetry_guard = telemetry::init_telemetry();
+    let otel_enabled = telemetry_guard.otel_enabled();
+
+    let exit_code = run_main(otel_enabled);
+
+    // std::process::exit terminates the process without running Drops for
+    // values still on the stack, so the TelemetryGuard's Drop (which flushes
+    // buffered OTLP spans) would be skipped. Drop explicitly first.
+    drop(telemetry_guard);
+
+    std::process::exit(exit_code);
+}
+
+fn run_main(otel_enabled: bool) -> i32 {
     let cli = cli::parse_with_default().unwrap_or_else(|err| err.exit());
 
     let log_level_filter = cli.verbose.log_level_filter();
 
-    let stdout_logger = env_logger::Builder::new()
-        .format(|buf, record| writeln!(buf, "{}:\n{}", record.level(), record.args()))
-        .filter_level(log_level_filter)
-        .target(env_logger::fmt::Target::Stdout)
-        .build();
-
-    let stderr_logger = env_logger::Builder::new()
-        .format(|buf, record| writeln!(buf, "{}:\n{}", record.level(), record.args()))
-        .filter_level(log_level_filter)
-        .target(env_logger::fmt::Target::Stderr)
-        .build();
-
-    log::set_max_level(log_level_filter);
-    log::set_boxed_logger(Box::new(SplitLogger {
-        stdout: stdout_logger,
-        stderr: stderr_logger,
-    }))
-    .expect("Failed to initialize logger");
+    // Only set up custom logger if OTEL is not enabled (OTEL sets up its own subscriber)
+    if !otel_enabled {
+        let stdout_logger = env_logger::Builder::new()
+            .format(|buf, record| writeln!(buf, "{}:\n{}", record.level(), record.args()))
+            .filter_level(log_level_filter)
+            .target(env_logger::fmt::Target::Stdout)
+            .build();
+
+        let stderr_logger = env_logger::Builder::new()
+            .format(|buf, record| writeln!(buf, "{}:\n{}", record.level(), record.args()))
+            .filter_level(log_level_filter)
+            .target(env_logger::fmt::Target::Stderr)
+            .build();
+
+        log::set_max_level(log_level_filter);
+        log::set_boxed_logger(Box::new(SplitLogger {
+            stdout: stdout_logger,
+            stderr: stderr_logger,
+        }))
+        .expect("Failed to initialize logger");
+    }
 
     let is_tty: bool = Term::stdout().is_term() && Term::stderr().is_term();
     let plain_output = !is_tty;
@@ -42,36 +60,29 @@ fn main() -> Result<()> {
 
     match cli.command {
         cli::Command::CompilerArgs { path } => {
-            println!("{}", build::get_compiler_args(Path::new(&path))?);
-            std::process::exit(0);
+            exit_code(build::get_compiler_args(Path::new(&path)).map(|args| println!("{}", args)))
         }
         cli::Command::Build(build_args) => {
-            match build::build(
+            let result = build::build(
                 &build_args.filter,
-                Path::new(&build_args.folder as &str),
+                build_args.folder.as_ref(),
                 show_progress,
                 build_args.no_timing,
                 true, // create_sourcedirs is now always enabled
                 plain_output,
                 (*build_args.warn_error).clone(),
                 build_args.prod,
-            ) {
-                Err(e) => {
-                    eprintln!("{:#}", e);
-                    std::process::exit(1)
-                }
-                Ok(_) => {
-                    if let Some(args_after_build) = (*build_args.after_build).clone() {
-                        cmd::run(args_after_build)
-                    }
-                    std::process::exit(0)
-                }
-            };
+            );
+            if result.is_ok()
+                && let Some(args_after_build) = (*build_args.after_build).clone()
+            {
+                cmd::run(args_after_build);
+            }
+            exit_code(result.map(|_| ()))
         }
         cli::Command::Watch(watch_args) => {
             let _lock = get_lock_or_exit(LockKind::Watch, &watch_args.folder);
-
-            match watcher::start(
+            exit_code(watcher::start(
                 &watch_args.filter,
                 show_progress,
                 &watch_args.folder,
@@ -80,22 +91,31 @@ fn main() -> Result<()> {
                 plain_output,
                 (*watch_args.warn_error).clone(),
                 watch_args.prod,
-            ) {
-                Err(e) => {
-                    eprintln!("{:#}", e);
-                    std::process::exit(1)
-                }
-                Ok(_) => Ok(()),
-            }
+            ))
         }
         cli::Command::Clean { folder, prod } => {
             let _lock = get_lock_or_exit(LockKind::Build, &folder);
-            let result = build::clean::clean(Path::new(&folder as &str), show_progress, plain_output, prod);
-            let _lock = drop_lock(LockKind::Build, &folder);
+            let code = exit_code(build::clean::clean(
+                folder.as_ref(),
+                show_progress,
+                plain_output,
+                prod,
+            ));
+            let _ = drop_lock(LockKind::Build, &folder);
+            code
+        }
+        cli::Command::Format { stdin, check, files } => exit_code(format::format(stdin, check, files)),
+    }
+}
 
-            result
+/// Map a command's Result<()> to a process exit code, printing the error on failure.
+fn exit_code(result: Result<()>) -> i32 {
+    match result {
+        Ok(()) => 0,
+        Err(e) => {
+            eprintln!("{:#}", e);
+            1
         }
-        cli::Command::Format { stdin, check, files } => format::format(stdin, check, files),
     }
 }
 
diff --git a/rewatch/src/telemetry.rs b/rewatch/src/telemetry.rs
new file mode 100644
index 0000000000..0af6c20b5e
--- /dev/null
+++ b/rewatch/src/telemetry.rs
@@ -0,0 +1,164 @@
+//! OpenTelemetry setup for rewatch.
+//!
+//! Provides optional tracing export via OTLP HTTP when OTEL_EXPORTER_OTLP_ENDPOINT is set.
+//! When the environment variable is not set, tracing is disabled (no-op).
+
+use opentelemetry::trace::TracerProvider as _;
+use opentelemetry_otlp::{Protocol, SpanExporter, WithExportConfig};
+use opentelemetry_sdk::Resource;
+use opentelemetry_sdk::trace::SdkTracerProvider;
+use tracing_subscriber::EnvFilter;
+use tracing_subscriber::fmt;
+use tracing_subscriber::layer::SubscriberExt;
+use tracing_subscriber::util::SubscriberInitExt;
+
+/// Guard that ensures telemetry is properly flushed and shut down.
+/// Drop this at the end of main to flush all spans.
+pub struct TelemetryGuard {
+    provider: Option<SdkTracerProvider>,
+    /// Whether OTEL tracing was initialized (affects logger setup in main).
+    otel_enabled: bool,
+}
+
+impl TelemetryGuard {
+    /// Returns whether OTLP span export was successfully initialized.
+    pub fn otel_enabled(&self) -> bool {
+        self.otel_enabled
+    }
+}
+
+impl Drop for TelemetryGuard {
+    fn drop(&mut self) {
+        if let Some(provider) = self.provider.take() {
+            // Force flush - this exports any buffered spans
+            if let Err(e) = provider.force_flush() {
+                log::warn!("Error flushing tracer provider: {}", e);
+            }
+            // Shutdown
+            if let Err(e) = provider.shutdown() {
+                log::warn!("Error shutting down tracer provider: {}", e);
+            }
+        }
+    }
+}
+
+/// Initialize OpenTelemetry tracing if OTEL_EXPORTER_OTLP_ENDPOINT is set.
+///
+/// Returns a guard that must be kept alive for the duration of the program.
+/// When the guard is dropped, it flushes all pending spans.
+///
+/// If OTEL_EXPORTER_OTLP_ENDPOINT is not set, returns a no-op guard and
+/// tracing calls become no-ops.
+pub fn init_telemetry() -> TelemetryGuard {
+    // Presence of either the general or trace-specific endpoint env var enables OTLP export.
+    let enabled = std::env::var_os("OTEL_EXPORTER_OTLP_ENDPOINT").is_some()
+        || std::env::var_os("OTEL_EXPORTER_OTLP_TRACES_ENDPOINT").is_some();
+
+    if enabled { init_with_otlp() } else { init_noop() }
+}
+
+/// Initialize with OTLP exporter.
+fn init_with_otlp() -> TelemetryGuard {
+    // Build a blocking reqwest-backed HTTP exporter. Blocking is fine here
+    // because the batch span processor runs in its own background thread.
+    //
+    // The exporter reads OTEL_EXPORTER_OTLP_TRACES_ENDPOINT (used verbatim)
+    // or falls back to OTEL_EXPORTER_OTLP_ENDPOINT (with /v1/traces appended),
+    // matching the OTEL spec — so we pass no explicit endpoint here.
+    let exporter = match SpanExporter::builder()
+        .with_http()
+        .with_protocol(Protocol::HttpBinary)
+        .build()
+    {
+        Ok(exp) => exp,
+        Err(e) => {
+            log::warn!("Failed to create OTLP exporter: {}. Falling back to no-op.", e);
+            return init_noop();
+        }
+    };
+
+    // Resource::builder() applies the SdkProvidedResourceDetector and
+    // EnvResourceDetector, which already pick up OTEL_SERVICE_NAME and
+    // OTEL_RESOURCE_ATTRIBUTES from the environment. Only default
+    // service.name = "rewatch" when the user hasn't supplied their own.
+    let mut resource_builder = Resource::builder();
+    if std::env::var_os("OTEL_SERVICE_NAME").is_none() {
+        resource_builder = resource_builder.with_service_name("rewatch");
+    }
+    let resource = resource_builder.build();
+
+    let provider = SdkTracerProvider::builder()
+        .with_batch_exporter(exporter)
+        .with_resource(resource)
+        .build();
+
+    // Bridge the `tracing` crate into this provider.
+    let tracer = provider.tracer("rewatch");
+    let telemetry_layer = tracing_opentelemetry::layer().with_tracer(tracer);
+
+    // Default to debug level so that diagnostic tracing::debug! events
+    // (e.g. in the watcher) are captured as OTEL span events.
+    let filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new("debug"));
+
+    // Also write logs to stderr. Without this layer, `log::*` / `tracing::*`
+    // output is silently swallowed when telemetry is enabled, since the
+    // OTEL layer only exports spans — it does not print them.
+    let fmt_layer = fmt::layer().with_writer(std::io::stderr);
+
+    tracing_subscriber::registry()
+        .with(filter)
+        .with(telemetry_layer)
+        .with(fmt_layer)
+        .init();
+
+    TelemetryGuard {
+        provider: Some(provider),
+        otel_enabled: true,
+    }
+}
+
+/// Initialize with no-op tracing (no export).
+fn init_noop() -> TelemetryGuard {
+    // Don't set up any subscriber - let main.rs handle logging normally
+    TelemetryGuard {
+        provider: None,
+        otel_enabled: false,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn noop_guard_reports_otel_disabled() {
+        let guard = init_noop();
+        assert!(!guard.otel_enabled());
+        // Explicit drop — must not panic with provider == None.
+        drop(guard);
+    }
+
+    #[test]
+    fn noop_guard_drops_cleanly_without_explicit_shutdown() {
+        // Implicit drop at end of scope: exercises Drop with no provider.
+        let _guard = init_noop();
+    }
+
+    #[test]
+    fn init_telemetry_without_env_is_noop() {
+        // SAFETY: These env vars are process-global; tests run serially in a
+        // single thread by default for this crate (no #[test(flavor = ...)]).
+        // If parallelised later, wrap in a Mutex.
+        // Ensure the env is clean for this check.
+        unsafe {
+            std::env::remove_var("OTEL_EXPORTER_OTLP_ENDPOINT");
+            std::env::remove_var("OTEL_EXPORTER_OTLP_TRACES_ENDPOINT");
+        }
+
+        let guard = init_telemetry();
+        assert!(
+            !guard.otel_enabled(),
+            "expected no-op guard when OTEL endpoint env vars are unset"
+        );
+    }
+}
diff --git a/rewatch/src/watcher.rs b/rewatch/src/watcher.rs
index d6aba426f9..130a62fec1 100644
--- a/rewatch/src/watcher.rs
+++ b/rewatch/src/watcher.rs
@@ -267,6 +267,12 @@ async fn async_watch(
                 )
             {
                 log::debug!("rescript.json changed -> full compile");
+                tracing::debug!(
+                    reason = "rescript.json changed",
+                    event_kind = ?event.kind,
+                    paths = ?event.paths,
+                    "watcher.full_compile_triggered"
+                );
                 needs_compile_type = CompileType::Full;
                 continue;
             }
@@ -473,6 +479,7 @@ async fn async_watch(
 }
 
 #[allow(clippy::too_many_arguments)]
+#[tracing::instrument(name = "rewatch.watch", skip_all, fields(working_dir = %folder))]
 pub fn start(
     filter: &Option<regex::Regex>,
     show_progress: bool,