diff --git a/.pre-commit-hooks.yaml b/.pre-commit-hooks.yaml
new file mode 100644
index 0000000..6cde7a0
--- /dev/null
+++ b/.pre-commit-hooks.yaml
@@ -0,0 +1,6 @@
+- id: gwp-basis-check
+  name: Check labelled GWP values
+  entry: python3 gwp_basis_check_hook.py
+  language: system
+  pass_filenames: true
+  files: \.(?:py|ts|js|json|md|html?|csv|tsv|ya?ml)$
diff --git a/README.md b/README.md
index 180e012..1ce0115 100644
--- a/README.md
+++ b/README.md
@@ -145,6 +145,36 @@ python3 gwp_basis_check.py --self-test
 
 Exit codes: `0` nothing found · `1` findings · `2` nothing was checkable.
 
+### Run it with pre-commit
+
+Add this repository to a project's `.pre-commit-config.yaml`:
+
+```yaml
+- repo: https://github.com/greencalculus/gwp-basis-check
+  rev: v1
+  hooks:
+    - id: gwp-basis-check
+```
+
+The hook considers common source, table and documentation formats. A finding
+blocks the commit; `NOT CHECKED` does not, because most ordinary files do not
+contain a labelled GWP table.
+
+### Run it in GitHub Actions
+
+Use the composite action with one or more space-separated paths or glob
+patterns:
+
+```yaml
+- uses: greencalculus/gwp-basis-check@v1
+  with:
+    paths: 'src/**/*.py data/*.csv'
+```
+
+As with the hook, unmatched or unreadable shapes remain visibly `NOT CHECKED`
+without failing unrelated CI; a finding or a genuine runtime failure still
+fails the step.
+
 ## What file formats does it read?
 
 - a record carrying a gas name plus `ar4`/`ar5`/`ar6` fields — JSON, TypeScript, Python, SQL seed rows
diff --git a/action.yml b/action.yml
new file mode 100644
index 0000000..97c6046
--- /dev/null
+++ b/action.yml
@@ -0,0 +1,39 @@
+name: GWP basis check
+description: Check labelled GWP values against the IPCC report they name.
+
+inputs:
+  paths:
+    description: Space-separated file paths or glob patterns to check.
+    required: false
+    default: "**/*.{py,ts,js,json,md,html,csv,tsv,yml,yaml}"
+
+runs:
+  using: composite
+  steps:
+    - name: Check labelled GWP values
+      shell: bash
+      run: |
+        shopt -s globstar nullglob
+        files=()
+        for pattern in ${{ inputs.paths }}; do
+          matches=( $pattern )
+          files+=( "${matches[@]}" )
+        done
+
+        status=2
+        if (( ${#files[@]} )); then
+          set +e
+          python3 "$GITHUB_ACTION_PATH/gwp_basis_check.py" "${files[@]}"
+          status=$?
+          set -e
+        else
+          echo "NOT CHECKED — no paths matched the supplied patterns."
+        fi
+
+        # 2 is an expected no-match result, not a failed CI check. Preserve
+        # other non-zero statuses so a genuine action/runtime failure is not
+        # mistaken for a clean scan.
+        if [[ "$status" -eq 0 || "$status" -eq 2 ]]; then
+          exit 0
+        fi
+        exit "$status"
diff --git a/gwp_basis_check.py b/gwp_basis_check.py
index c8b37d3..cb6f061 100644
--- a/gwp_basis_check.py
+++ b/gwp_basis_check.py
@@ -415,6 +415,7 @@ def check_reference():
 
 def self_test():
     import tempfile, os
+    from gwp_basis_check_hook import hook_exit_code
     ok = True
     print("REFERENCE INTEGRITY")
     errs = check_reference()
@@ -436,6 +437,10 @@ def self_test():
         ok &= good
         print(f"  [{'PASS' if good else 'FAIL'}] {label[:58]:60} "
               f"{'got ' + str(sorted(types)) if types else 'clean'}")
+    hook_good = (hook_exit_code(0) == 0 and hook_exit_code(1) == 1
+                 and hook_exit_code(2) == 0)
+    ok &= hook_good
+    print(f"  [{'PASS' if hook_good else 'FAIL'}] pre-commit permits NOT CHECKED results")
     print(f"\nreference {REF.get('version')} · reports {'/'.join(b.upper() for b in BASES)}")
     print("ALL PASS" if ok else "FAILURES ABOVE")
     return 0 if ok else 1
diff --git a/gwp_basis_check_hook.py b/gwp_basis_check_hook.py
new file mode 100644
index 0000000..06981bf
--- /dev/null
+++ b/gwp_basis_check_hook.py
@@ -0,0 +1,19 @@
+"""The pre-commit entry point: findings block, unreadable files do not."""
+
+import sys
+
+from gwp_basis_check import main
+
+
+def hook_exit_code(status):
+    """Map the checker result to the pre-commit contract.
+
+    Exit 2 means a file was not in a form this checker can read.  That is an
+    expected result when a broad pre-commit file filter sees an ordinary source
+    file, so it must not reject the commit.  Findings (1) still block it.
+    """
+    return 0 if status == 2 else status
+
+
+if __name__ == "__main__":
+    sys.exit(hook_exit_code(main()))