diff --git a/.github/workflows/secret-scan.yml b/.github/workflows/secret-scan.yml
new file mode 100644
index 0000000..ce7f57e
--- /dev/null
+++ b/.github/workflows/secret-scan.yml
@@ -0,0 +1,35 @@
+name: secret scan
+
+on:
+  # Only the default branch on push; PR branches are covered by pull_request,
+  # so a branch with an open PR is not scanned twice for the same commit.
+  push:
+    branches: [main]
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: secret-scan-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  secret-scan:
+    name: Gitleaks
+    # macOS runner: Homebrew is preinstalled, so gitleaks installs without any
+    # third-party action. Standard runners are free on public repositories.
+    runs-on: macos-latest
+    timeout-minutes: 20
+    steps:
+      - name: Check out full history
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - name: Install gitleaks
+        run: brew install gitleaks
+
+      - name: Scan published history
+        run: bash scripts/check-secrets.sh
diff --git a/scripts/check-secrets.sh b/scripts/check-secrets.sh
new file mode 100755
index 0000000..ca338b0
--- /dev/null
+++ b/scripts/check-secrets.sh
@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+# Public-source secret gate.
+#
+# Scans the content this repository actually publishes -- the git-tracked
+# worktree -- with Gitleaks. Candidate values are never printed (--redact=100).
+#
+# Scope: tracked files, not full history. This gate exists to stop something
+# new from being published. Existing history was audited separately; scanning
+# it here would hold the gate permanently red on old commits that have already
+# been reviewed and cannot be rewritten without breaking forks and clones.
+#
+# Gitleaks only, deliberately. TruffleHog without verification flags ordinary
+# identifiers (it trips on Swift test-method names), and running it *with*
+# verification would send candidate secrets off-box.
+#
+# Reviewed non-secrets belong in .gitleaks.toml, not in an exception here.
+set -euo pipefail
+
+# Non-interactive shells (CI, ssh) often omit Homebrew from PATH.
+for tool_directory in /opt/homebrew/bin /usr/local/bin; do
+  [[ -d "${tool_directory}" ]] && PATH="${tool_directory}:${PATH}"
+done
+export PATH
+
+repo_root="$(git -C "$(dirname "${BASH_SOURCE[0]}")/.." rev-parse --show-toplevel)"
+
+command -v gitleaks >/dev/null || {
+  printf 'secret gate: gitleaks is required but was not found\n' >&2
+  exit 2
+}
+
+# Snapshot only tracked files, so gitignored local material (real .env files,
+# build output, caches) is never scanned and never reported.
+snapshot="$(mktemp -d "${TMPDIR:-/tmp}/secret-gate.XXXXXX")"
+cleanup() { rm -rf -- "${snapshot}"; }
+trap cleanup EXIT HUP INT TERM
+
+while IFS= read -r -d '' tracked_path; do
+  [[ -f "${repo_root}/${tracked_path}" ]] || continue
+  mkdir -p "${snapshot}/$(dirname "${tracked_path}")"
+  cp -p "${repo_root}/${tracked_path}" "${snapshot}/${tracked_path}"
+done < <(git -C "${repo_root}" ls-files -z)
+
+if [[ -f "${repo_root}/.gitleaks.toml" ]]; then
+  gitleaks dir \
+    --no-banner \
+    --redact=100 \
+    --config "${repo_root}/.gitleaks.toml" \
+    "${snapshot}"
+else
+  gitleaks dir \
+    --no-banner \
+    --redact=100 \
+    "${snapshot}"
+fi
+
+printf 'PASS: Gitleaks found no secrets in the tracked worktree.\n'