diff --git a/.githooks/pre-commit b/.githooks/pre-commit
new file mode 100755
index 0000000..27db6b0
--- /dev/null
+++ b/.githooks/pre-commit
@@ -0,0 +1,25 @@
+#!/usr/bin/env sh
+# Secret scanner — LAC-2555
+#
+# Blocks commits that introduce plaintext credentials.
+# Requires `gitleaks` locally; if not installed we print a warning and
+# fall through — CI still runs the same scan on the PR, so this is
+# defense-in-depth, not the only gate.
+#
+# Install:
+#   macOS   → brew install gitleaks
+#   linux   → https://github.com/gitleaks/gitleaks/releases
+
+if command -v gitleaks >/dev/null 2>&1; then
+  if ! gitleaks protect --staged --redact --no-banner; then
+    echo ""
+    echo "gitleaks found a potential secret in staged changes."
+    echo "If real: rotate the credential first, then remove it from the diff."
+    echo "If a false positive: extend .gitleaks.toml allowlist or add an inline"
+    echo "'gitleaks:allow' comment. Do not disable the hook."
+    exit 1
+  fi
+else
+  echo "gitleaks not installed — skipping local secret scan (CI still runs)."
+  echo "  install: brew install gitleaks"
+fi
diff --git a/.github/workflows/gitleaks.yml b/.github/workflows/gitleaks.yml
new file mode 100644
index 0000000..235c0ec
--- /dev/null
+++ b/.github/workflows/gitleaks.yml
@@ -0,0 +1,30 @@
+# Secret scan — LAC-2555
+#
+# Fails the PR/push if plaintext credentials appear in the diff.
+# Config lives in .gitleaks.toml at the repo root.
+#
+# Local defense-in-depth: .husky/pre-commit runs the same tool on staged
+# changes when the gitleaks binary is installed.
+
+name: gitleaks
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  gitleaks:
+    name: gitleaks
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+      - uses: gitleaks/gitleaks-action@v2
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
diff --git a/.gitleaks.toml b/.gitleaks.toml
new file mode 100644
index 0000000..ca606d3
--- /dev/null
+++ b/.gitleaks.toml
@@ -0,0 +1,23 @@
+# gitleaks config — LAC-2555
+#
+# Extends the built-in rule set. Allowlist covers files that legitimately
+# contain placeholder credentials (example env files, docs, changelogs).
+# When you add a new placeholder file that trips gitleaks, extend the
+# `paths` list here rather than removing the scan.
+
+[extend]
+useDefault = true
+
+[allowlist]
+description = "Placeholder-credential files and generated docs"
+paths = [
+  '''(^|/)\.env\.example(\..+)?$''',
+  '''(^|/)\.env\.example\.local$''',
+  '''(^|/)\.env\.test$''',
+  '''(^|/)\.env\.example\.production$''',
+  '''(^|/)README\.md$''',
+  '''(^|/)CHANGELOG\.md$''',
+  '''(^|/)LICENSE$''',
+  '''(^|/)docs/''',
+  '''(^|/)public/llms(-full)?\.txt$''',
+]
diff --git a/package.json b/package.json
index d554b3d..bbfd941 100644
--- a/package.json
+++ b/package.json
@@ -50,7 +50,8 @@
     "test:coverage": "vitest run --coverage",
     "test:browser": "vitest --config=vitest.config.browser.ts",
     "test:node": "vitest --config=vitest.config.node.ts",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit",
+    "postinstall": "git config core.hooksPath .githooks 2>/dev/null || true"
   },
   "dependencies": {
     "@auth/drizzle-adapter": "1.11.1",