diff --git a/.githooks/pre-commit b/.githooks/pre-commit
new file mode 100755
index 0000000..ce54c8b
--- /dev/null
+++ b/.githooks/pre-commit
@@ -0,0 +1,5 @@
+#!/bin/sh
+set -eu
+
+repo_root=$(git rev-parse --show-toplevel)
+exec "$repo_root/scripts/secret-scan.sh" staged
diff --git a/.github/workflows/secret-scan.yml b/.github/workflows/secret-scan.yml
new file mode 100644
index 0000000..6174b1b
--- /dev/null
+++ b/.github/workflows/secret-scan.yml
@@ -0,0 +1,41 @@
+name: Secret scan
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  gitleaks:
+    name: Gitleaks working tree and history
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - name: Check out complete history
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
+        with:
+          fetch-depth: 0
+
+      - name: Install verified Gitleaks binary
+        env:
+          GITLEAKS_VERSION: 8.30.1
+        run: |
+          set -euo pipefail
+          archive="gitleaks_${GITLEAKS_VERSION}_linux_x64.tar.gz"
+          base="https://github.com/gitleaks/gitleaks/releases/download/v${GITLEAKS_VERSION}"
+          curl --fail --silent --show-error --location --output "$RUNNER_TEMP/$archive" "$base/$archive"
+          curl --fail --silent --show-error --location --output "$RUNNER_TEMP/checksums.txt" "$base/gitleaks_${GITLEAKS_VERSION}_checksums.txt"
+          cd "$RUNNER_TEMP"
+          grep "  $archive$" checksums.txt | sha256sum --check --strict
+          tar --extract --gzip --file "$archive" gitleaks
+          chmod 700 gitleaks
+
+      - name: Scan working tree and full Git history
+        env:
+          GITLEAKS_BIN: ${{ runner.temp }}/gitleaks
+        run: ./scripts/secret-scan.sh all
diff --git a/.gitleaks.toml b/.gitleaks.toml
new file mode 100644
index 0000000..bf5dc3b
--- /dev/null
+++ b/.gitleaks.toml
@@ -0,0 +1,4 @@
+title = "Repository secret scanning"
+
+[extend]
+useDefault = true
diff --git a/SECURITY.md b/SECURITY.md
new file mode 100644
index 0000000..20c4af7
--- /dev/null
+++ b/SECURITY.md
@@ -0,0 +1,35 @@
+# Security and secret handling
+
+Live credentials, private keys, bearer values, recovery material, and
+secret-bearing production exports do not belong in this repository, whether it
+is private or public.
+
+## Secret scanning
+
+Install Gitleaks and run:
+
+```bash
+./scripts/secret-scan.sh staged
+./scripts/secret-scan.sh all
+```
+
+Enable the versioned local pre-commit hook with:
+
+```bash
+git config core.hooksPath .githooks
+```
+
+The hook fails closed when Gitleaks is unavailable. CI downloads the pinned
+Gitleaks release, verifies its upstream checksum, and scans both the working
+tree and complete fetched history with read-only repository permissions.
+
+Do not bypass a failed scan. If a finding is real, revoke or rotate it first,
+then remove the material and rescan. Do not copy a credential into an issue,
+pull request, log, or remediation note. Any allowlist exception must be narrow
+to the exact rule, path, and proven synthetic or false-positive value.
+
+Before making a private repository public, also review every branch and tag,
+Git LFS and submodule content, release and Actions artifacts, generated
+archives, source maps, notebooks, fixtures, logs, screenshots, workflows, and
+private topology. Repeat the scan from a fresh clone and obtain repository-owner
+approval before changing visibility.
diff --git a/scripts/secret-scan.sh b/scripts/secret-scan.sh
new file mode 100755
index 0000000..105ba90
--- /dev/null
+++ b/scripts/secret-scan.sh
@@ -0,0 +1,64 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+mode="${1:-all}"
+repo_root=$(git rev-parse --show-toplevel)
+gitleaks_bin="${GITLEAKS_BIN:-gitleaks}"
+
+if [[ "$gitleaks_bin" == */* ]]; then
+  if [[ ! -x "$gitleaks_bin" ]]; then
+    printf 'error: Gitleaks executable not found at %s\n' "$gitleaks_bin" >&2
+    exit 2
+  fi
+elif ! command -v "$gitleaks_bin" >/dev/null 2>&1; then
+  printf 'error: gitleaks is required; install it or set GITLEAKS_BIN\n' >&2
+  exit 2
+fi
+
+common=(
+  --no-banner
+  --no-color
+  --redact
+  --config "$repo_root/.gitleaks.toml"
+)
+
+scan_staged() {
+  (
+    cd "$repo_root"
+    "$gitleaks_bin" git "${common[@]}" --pre-commit --staged .
+  )
+}
+
+scan_tree() {
+  (
+    cd "$repo_root"
+    "$gitleaks_bin" dir "${common[@]}" .
+  )
+}
+
+scan_history() {
+  (
+    cd "$repo_root"
+    "$gitleaks_bin" git "${common[@]}" --log-opts="--all" .
+  )
+}
+
+case "$mode" in
+  staged)
+    scan_staged
+    ;;
+  tree)
+    scan_tree
+    ;;
+  history)
+    scan_history
+    ;;
+  all)
+    scan_tree
+    scan_history
+    ;;
+  *)
+    printf 'usage: %s [staged|tree|history|all]\n' "$0" >&2
+    exit 2
+    ;;
+esac