diff --git a/.github/workflows/format.yml b/.github/workflows/format.yml
new file mode 100644
index 0000000..6d594a9
--- /dev/null
+++ b/.github/workflows/format.yml
@@ -0,0 +1,26 @@
+name: Format
+
+on:
+  push:
+    branches: [ "master" ]
+  pull_request:
+    branches: [ "master" ]
+
+jobs:
+  clang-format:
+
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+
+    steps:
+    - uses: actions/checkout@v7
+
+    # Pinned so a new clang-format release cannot reformat the tree in CI.
+    - name: Install clang-format
+      run: sudo apt-get install -y clang-format-18
+
+    - name: Check formatting
+      env:
+        CLANG_FORMAT: clang-format-18
+      run: ./format.sh --check
diff --git a/format.sh b/format.sh
new file mode 100755
index 0000000..e4eebd3
--- /dev/null
+++ b/format.sh
@@ -0,0 +1,16 @@
+#!/bin/sh
+
+# Formats the shader sources in place with clang-format.
+# Pass --check to report problems without writing.
+# Set CLANG_FORMAT to pick a version, e.g. CLANG_FORMAT=clang-format-18.
+
+: "${CLANG_FORMAT:=clang-format}"
+
+if [ "$1" = "--check" ]; then
+    shift
+    set -- --dry-run --Werror "$@"
+else
+    set -- -i "$@"
+fi
+
+find shaders -type f \( -name '*.fsh' -o -name '*.vsh' -o -name '*.glsl' \) -exec "$CLANG_FORMAT" "$@" -- {} +