codeql skill

CodeQL Code Scanning

This skill provides procedural guidance for configuring and running CodeQL code scanning — both through GitHub Actions workflows and the standalone CodeQL CLI.

When to Use This Skill

Use this skill when the request involves:

• Creating or customizing a codeql.yml GitHub Actions workflow
• Choosing between default setup and advanced setup for code scanning
• Configuring CodeQL language matrix, build modes, or query suites
• Running CodeQL CLI locally (codeql database create, database analyze, github upload-results)
• Understanding or interpreting SARIF output from CodeQL
• Troubleshooting CodeQL analysis failures (build modes, compiled languages, runner requirements)
• Setting up CodeQL for monorepos with per-component scanning
• Configuring dependency caching, custom query packs, or model packs

Supported Languages

CodeQL supports the following language identifiers:

Alternative identifiers are equivalent to the standard identifier (e.g., javascript does not exclude TypeScript analysis).

Core Workflow — GitHub Actions

Step 1: Choose Setup Type

• Default setup — Enable from repository Settings → Advanced Security → CodeQL analysis. Best for getting started quickly. Uses none build mode for most languages.
• Advanced setup — Create a .github/workflows/codeql.yml file for full control over triggers, build modes, query suites, and matrix strategies.

To switch from default to advanced: disable default setup first, then commit the workflow file.

Step 2: Configure Workflow Triggers

Define when scanning runs:

on:
  push:
    branches: [main, protected]
  pull_request:
    branches: [main]
  schedule:
    - cron: '30 6 * * 1'  # Weekly Monday 6:30 UTC

• push — scans on every push to specified branches; results appear in Security tab
• pull_request — scans PR merge commits; results appear as PR check annotations
• schedule — periodic scans of the default branch (cron must exist on default branch)
• merge_group — add if repository uses merge queues

To skip scans for documentation-only PRs:

on:
  pull_request:
    paths-ignore:
      - '**/*.md'
      - '**/*.txt'

paths-ignore controls whether the workflow runs, not which files are analyzed.

Step 3: Configure Permissions

Set least-privilege permissions:

permissions:
  security-events: write   # Required to upload SARIF results
  contents: read            # Required to checkout code
  actions: read             # Required for private repos using codeql-action

Step 4: Configure Language Matrix

Use a matrix strategy to analyze each language in parallel:

jobs:
  analyze:
    name: Analyze (${{ matrix.language }})
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        include:
          - language: javascript-typescript
            build-mode: none
          - language: python
            build-mode: none

For compiled languages, set the appropriate build-mode:

• none — no build required (supported for C/C++, C#, Java, Rust)
• autobuild — automatic build detection
• manual — custom build commands (advanced setup only)

For detailed per-language autobuild behavior and runner requirements, search references/compiled-languages.md.

Step 5: Configure CodeQL Init and Analysis

steps:
  - name: Checkout repository
    uses: actions/checkout@v4

  - name: Initialize CodeQL
    uses: github/codeql-action/init@v4
    with:
      languages: ${{ matrix.language }}
      build-mode: ${{ matrix.build-mode }}
      queries: security-extended
      dependency-caching: true

  - name: Perform CodeQL Analysis
    uses: github/codeql-action/analyze@v4
    with:
      category: "/language:${{ matrix.language }}"

Query suite options:

• security-extended — default security queries plus additional coverage
• security-and-quality — security plus code quality queries
• Custom query packs via packs: input (e.g., codeql/javascript-queries:AlertSuppression.ql)

Dependency caching: Set dependency-caching: true on the init action to cache restored dependencies across runs.

Analysis category: Use category to distinguish SARIF results in monorepos (e.g., per-language, per-component).

Step 6: Monorepo Configuration

For monorepos with multiple components, use the category parameter to separate SARIF results:

category: "/language:${{ matrix.language }}/component:frontend"

To restrict analysis to specific directories, use a CodeQL configuration file (.github/codeql/codeql-config.yml):

paths:
  - apps/
  - services/
paths-ignore:
  - node_modules/
  - '**/test/**'

Reference it in the workflow:

- uses: github/codeql-action/init@v4
  with:
    config-file: .github/codeql/codeql-config.yml

Step 7: Manual Build Steps (Compiled Languages)

If autobuild fails or custom build commands are needed:

- language: c-cpp
  build-mode: manual

Then add explicit build steps between init and analyze:

- if: matrix.build-mode == 'manual'
  name: Build
  run: |
    make bootstrap
    make release

Core Workflow — CodeQL CLI

Step 1: Install the CodeQL CLI

Download the CodeQL bundle (includes CLI + precompiled queries):

# Download from https://github.com/github/codeql-action/releases
# Extract and add to PATH
export PATH="$HOME/codeql:$PATH"

# Verify installation
codeql resolve packs
codeql resolve languages

Always use the CodeQL bundle, not a standalone CLI download. The bundle ensures query compatibility and provides precompiled queries for better performance.

Step 2: Create a CodeQL Database

# Single language
codeql database create codeql-db \
  --language=javascript-typescript \
  --source-root=src

# Multiple languages (cluster mode)
codeql database create codeql-dbs \
  --db-cluster \
  --language=java,python \
  --command=./build.sh \
  --source-root=src

For compiled languages, provide the build command via --command.

Step 3: Analyze the Database

codeql database analyze codeql-db \
  javascript-code-scanning.qls \
  --format=sarif-latest \
  --sarif-category=javascript \
  --output=results.sarif

Common query suites: -code-scanning.qls, -security-extended.qls, -security-and-quality.qls.

Step 4: Upload Results to GitHub

codeql github upload-results \
  --repository=owner/repo \
  --ref=refs/heads/main \
  --commit=<commit-sha> \
  --sarif=results.sarif

Requires GITHUB_TOKEN environment variable with security-events: write permission.