diff --git a/.github/workflows/zig-ci.yml b/.github/workflows/zig-ci.yml
index 025ebb3..c5d1e98 100644
--- a/.github/workflows/zig-ci.yml
+++ b/.github/workflows/zig-ci.yml
@@ -27,6 +27,11 @@ on:
             {"os":"macos-latest","target":"macos-aarch64","zig_target":"aarch64-macos"},
             {"os":"windows-latest","target":"windows-x86_64","zig_target":"x86_64-windows"}
           ]
+      extra_targets_json:
+        description: JSON array of project-specific target entries appended to targets_json.
+        required: false
+        type: string
+        default: "[]"
       node_version:
         description: Optional Node.js version to install before custom commands.
         required: false
@@ -82,8 +87,34 @@ env:
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: "true"
 
 jobs:
+  targets:
+    name: Resolve target matrix
+    runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.merge.outputs.matrix }}
+
+    steps:
+      - name: Merge target matrices
+        id: merge
+        env:
+          TARGETS_JSON: ${{ inputs.targets_json }}
+          EXTRA_TARGETS_JSON: ${{ inputs.extra_targets_json }}
+        run: |
+          merged="$(jq -cn \
+            --argjson targets "${TARGETS_JSON}" \
+            --argjson extra "${EXTRA_TARGETS_JSON}" \
+            '$targets + $extra')"
+          jq -e 'type == "array" and length > 0 and all(.[]; type == "object" and has("os") and has("target") and has("zig_target") and ((has("build_args") | not) or (.build_args | type == "string")))' \
+            <<< "${merged}" >/dev/null
+          if [ "$(jq '[.[].target] | length' <<< "${merged}")" -ne "$(jq '[.[].target] | unique | length' <<< "${merged}")" ]; then
+            echo "target names must be unique across targets_json and extra_targets_json" >&2
+            exit 1
+          fi
+          echo "matrix=${merged}" >> "$GITHUB_OUTPUT"
+
   test:
     name: ${{ matrix.target }}
+    needs: targets
     runs-on: ${{ matrix.os }}
     defaults:
       run:
@@ -91,7 +122,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        include: ${{ fromJson(inputs.targets_json) }}
+        include: ${{ fromJson(needs.targets.outputs.matrix) }}
 
     steps:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
@@ -159,15 +190,18 @@ jobs:
       - name: Build ReleaseSmall
         env:
           EXTRA_BUILD_ARGS: ${{ inputs.build_args }}
+          TARGET_BUILD_ARGS: ${{ matrix.build_args }}
         run: |
           zig_args=(
             -Dtarget=${{ matrix.zig_target }}
             -Doptimize=ReleaseSmall
           )
-          if [ -n "${EXTRA_BUILD_ARGS}" ]; then
-            read -r -a extra_args <<< "${EXTRA_BUILD_ARGS}"
-            zig_args+=("${extra_args[@]}")
-          fi
+          for build_args in "${EXTRA_BUILD_ARGS}" "${TARGET_BUILD_ARGS}"; do
+            if [ -n "${build_args}" ]; then
+              read -r -a extra_args <<< "${build_args}"
+              zig_args+=("${extra_args[@]}")
+            fi
+          done
           zig build "${zig_args[@]}"
 
       - name: Run E2E command
diff --git a/.github/workflows/zig-nightly.yml b/.github/workflows/zig-nightly.yml
index 6124941..64f2e45 100644
--- a/.github/workflows/zig-nightly.yml
+++ b/.github/workflows/zig-nightly.yml
@@ -46,6 +46,11 @@ on:
             {"os":"windows-latest","target":"windows-x86_64","zig_target":"x86_64-windows","zig_cpu":"","ext":".exe"},
             {"os":"windows-latest","target":"windows-aarch64","zig_target":"aarch64-windows","zig_cpu":"","ext":".exe"}
           ]
+      extra_targets_json:
+        description: JSON array of project-specific nightly targets appended to targets_json.
+        required: false
+        type: string
+        default: "[]"
       node_version:
         description: Optional Node.js version to install before custom commands.
         required: false
@@ -114,6 +119,7 @@ jobs:
       short_sha: ${{ steps.version.outputs.short_sha }}
       artifact_prefix: ${{ steps.version.outputs.artifact_prefix }}
       built_at: ${{ steps.version.outputs.built_at }}
+      matrix: ${{ steps.targets.outputs.matrix }}
 
     steps:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
@@ -138,6 +144,24 @@ jobs:
           echo "value=nightly-${build_date}-${short_sha}" >> "$GITHUB_OUTPUT"
           echo "artifact_prefix=${artifact_prefix}" >> "$GITHUB_OUTPUT"
 
+      - name: Merge target matrices
+        id: targets
+        env:
+          TARGETS_JSON: ${{ inputs.targets_json }}
+          EXTRA_TARGETS_JSON: ${{ inputs.extra_targets_json }}
+        run: |
+          merged="$(jq -cn \
+            --argjson targets "${TARGETS_JSON}" \
+            --argjson extra "${EXTRA_TARGETS_JSON}" \
+            '$targets + $extra')"
+          jq -e 'type == "array" and length > 0 and all(.[]; type == "object" and has("os") and has("target") and has("zig_target") and ((has("build_args") | not) or (.build_args | type == "string")))' \
+            <<< "${merged}" >/dev/null
+          if [ "$(jq '[.[].target] | length' <<< "${merged}")" -ne "$(jq '[.[].target] | unique | length' <<< "${merged}")" ]; then
+            echo "target names must be unique across targets_json and extra_targets_json" >&2
+            exit 1
+          fi
+          echo "matrix=${merged}" >> "$GITHUB_OUTPUT"
+
       - name: Fetch previous successful workflow runs
         env:
           GH_TOKEN: ${{ github.token }}
@@ -181,7 +205,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        include: ${{ fromJson(inputs.targets_json) }}
+        include: ${{ fromJson(needs.preflight.outputs.matrix) }}
 
     steps:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
@@ -256,6 +280,7 @@ jobs:
         env:
           ANDROID_API_LEVEL: ${{ inputs.android_api_level }}
           EXTRA_BUILD_ARGS: ${{ inputs.build_args }}
+          TARGET_BUILD_ARGS: ${{ matrix.build_args }}
         run: |
           zig_target="${{ matrix.zig_target }}"
           if [[ "${{ matrix.target }}" == android-* ]]; then
@@ -273,10 +298,12 @@ jobs:
           if [[ "${{ matrix.target }}" == android-* ]]; then
             zig_args+=(--libc "${ZIG_ANDROID_LIBC_FILE}")
           fi
-          if [ -n "${EXTRA_BUILD_ARGS}" ]; then
-            read -r -a extra_args <<< "${EXTRA_BUILD_ARGS}"
-            zig_args+=("${extra_args[@]}")
-          fi
+          for build_args in "${EXTRA_BUILD_ARGS}" "${TARGET_BUILD_ARGS}"; do
+            if [ -n "${build_args}" ]; then
+              read -r -a extra_args <<< "${build_args}"
+              zig_args+=("${extra_args[@]}")
+            fi
+          done
           zig build "${zig_args[@]}"
 
       - name: Package nightly artifact
diff --git a/.github/workflows/zig-release.yml b/.github/workflows/zig-release.yml
index 4097184..74753fb 100644
--- a/.github/workflows/zig-release.yml
+++ b/.github/workflows/zig-release.yml
@@ -46,6 +46,11 @@ on:
             {"os":"windows-latest","target":"windows-x86_64","zig_target":"x86_64-windows","zig_cpu":"","ext":".exe"},
             {"os":"windows-latest","target":"windows-aarch64","zig_target":"aarch64-windows","zig_cpu":"","ext":".exe"}
           ]
+      extra_targets_json:
+        description: JSON array of project-specific release targets appended to targets_json.
+        required: false
+        type: string
+        default: "[]"
       node_version:
         description: Optional Node.js version to install before custom commands.
         required: false
@@ -104,8 +109,34 @@ env:
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: "true"
 
 jobs:
+  targets:
+    name: Resolve target matrix
+    runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.merge.outputs.matrix }}
+
+    steps:
+      - name: Merge target matrices
+        id: merge
+        env:
+          TARGETS_JSON: ${{ inputs.targets_json }}
+          EXTRA_TARGETS_JSON: ${{ inputs.extra_targets_json }}
+        run: |
+          merged="$(jq -cn \
+            --argjson targets "${TARGETS_JSON}" \
+            --argjson extra "${EXTRA_TARGETS_JSON}" \
+            '$targets + $extra')"
+          jq -e 'type == "array" and length > 0 and all(.[]; type == "object" and has("os") and has("target") and has("zig_target") and ((has("build_args") | not) or (.build_args | type == "string")))' \
+            <<< "${merged}" >/dev/null
+          if [ "$(jq '[.[].target] | length' <<< "${merged}")" -ne "$(jq '[.[].target] | unique | length' <<< "${merged}")" ]; then
+            echo "target names must be unique across targets_json and extra_targets_json" >&2
+            exit 1
+          fi
+          echo "matrix=${merged}" >> "$GITHUB_OUTPUT"
+
   build:
     name: Build (${{ matrix.target }})
+    needs: targets
     runs-on: ${{ matrix.os }}
     defaults:
       run:
@@ -113,7 +144,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        include: ${{ fromJson(inputs.targets_json) }}
+        include: ${{ fromJson(needs.targets.outputs.matrix) }}
 
     steps:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
@@ -206,6 +237,7 @@ jobs:
         env:
           ANDROID_API_LEVEL: ${{ inputs.android_api_level }}
           EXTRA_BUILD_ARGS: ${{ inputs.build_args }}
+          TARGET_BUILD_ARGS: ${{ matrix.build_args }}
         run: |
           zig_target="${{ matrix.zig_target }}"
           if [[ "${{ matrix.target }}" == android-* ]]; then
@@ -222,10 +254,12 @@ jobs:
           if [[ "${{ matrix.target }}" == android-* ]]; then
             zig_args+=(--libc "${ZIG_ANDROID_LIBC_FILE}")
           fi
-          if [ -n "${EXTRA_BUILD_ARGS}" ]; then
-            read -r -a extra_args <<< "${EXTRA_BUILD_ARGS}"
-            zig_args+=("${extra_args[@]}")
-          fi
+          for build_args in "${EXTRA_BUILD_ARGS}" "${TARGET_BUILD_ARGS}"; do
+            if [ -n "${build_args}" ]; then
+              read -r -a extra_args <<< "${build_args}"
+              zig_args+=("${extra_args[@]}")
+            fi
+          done
           zig build "${zig_args[@]}"
 
       - name: Upload artifact
diff --git a/README.md b/README.md
index 5ad05ee..5624dce 100644
--- a/README.md
+++ b/README.md
@@ -48,6 +48,30 @@ jobs:
         ]
 ```
 
+Use `targets_json` when a project needs to replace the default matrix. Use
+`extra_targets_json` to keep every default target and append only the targets
+specific to that project:
+
+```yaml
+jobs:
+  zig:
+    uses: nullclaw/nullbuilder/.github/workflows/zig-ci.yml@v1
+    permissions:
+      contents: read
+    with:
+      binary_name: nullclaw
+      artifact_prefix: nullclaw
+      extra_targets_json: >-
+        [
+          {"os":"ubuntu-latest","target":"linux-mipsel-musl","zig_target":"mipsel-linux-musleabi","build_args":"-Dembedded_wasm3=false"}
+        ]
+```
+
+`extra_targets_json` is available in the CI, nightly, and release workflows.
+Target names must remain unique after the two arrays are merged. An optional
+per-target `build_args` string is appended after the workflow-level build
+arguments and is useful when one architecture needs a feature override.
+
 ### Nightly
 
 ```yaml