diff --git a/Makefile b/Makefile
index 6a13e4a..e2aba04 100644
--- a/Makefile
+++ b/Makefile
@@ -35,7 +35,7 @@ test-all:
 
 .PHONY: test-fx
 test-fx: DOCKER_TAG=fx
-test-fx: _testcase-node _testcase-pnpm _testcase-deno _testcase-bun _testcase-php _testcase-php-coverage _testcase-python _testcase-golang _testcase-common
+test-fx: _testcase-node _testcase-pnpm _testcase-deno _testcase-bun _testcase-php _testcase-php-coverage _testcase-python _testcase-golang _testcase-t3code _testcase-common
 
 .PHONY: test-php
 test-php: DOCKER_TAG=php
@@ -90,6 +90,10 @@ _testcase-python:
 _testcase-golang:
 	$(TEST_RUN) go version
 
+.PHONY: _testcase-t3code
+_testcase-t3code:
+	$(TEST_RUN) t3 --version
+
 .PHONY: _testcase-common
 _testcase-common:
 	$(TEST_RUN) agent-browser --version
diff --git a/README.md b/README.md
index dc6bb6f..2ba1eaf 100644
--- a/README.md
+++ b/README.md
@@ -39,6 +39,7 @@ one tag per template:
 
 > Node.js (with `npm`) ships in every image because the shared AI CLIs are installed from npm.
 > The `nodejs` tag additionally provides Deno and Bun; only the `fx` tag adds `pnpm`.
+> The [T3 Code](https://github.com/pingdotgg/t3code) browser GUI (`t3`) is bundled only in the `fx` tag.
 
 ### Shared baseline
 
@@ -67,6 +68,9 @@ Choose this when a workspace is polyglot or you don’t want to commit to one st
 - **Python 3** with `pip` and `venv`.
 - **Go 1.26.5** (installed to `/usr/local/go`; `GOROOT`/`GOPATH`/PATH set for login shells).
 - **Rootless Docker** (docker-in-docker) — see [Rootless Docker](#rootless-docker) below.
+- **[T3 Code](https://github.com/pingdotgg/t3code)** (`t3`) — a browser GUI that drives the coding
+  agents (OpenCode, Claude, Codex). Serves a web UI on port `3773`; `t3 serve` runs it headless
+  (no browser popup). Only bundled in the `fx` tag.
 
 ### `dockette/coder:php`
 
diff --git a/fx/Dockerfile b/fx/Dockerfile
index ebff358..4fa0075 100644
--- a/fx/Dockerfile
+++ b/fx/Dockerfile
@@ -90,6 +90,8 @@ RUN \
     chmod 0755 /usr/local/bin/opencode && \
     # NPM: CODEX, COPILOT #######################################################
     npm install -g @openai/codex @github/copilot && \
+    # T3CODE (browser GUI for coding agents) ###################################
+    npm install -g t3 && \
     # PNPM ######################################################################
     npm install -g pnpm && \
     # AGENT-BROWSER ##############################################################