Show HN: Easily reduce GitHub Actions costs with Ubuntu-slim migration

GitHub Actions recently introduced the lightweight ubuntu-slim runner (1 vCPU / 5 GB RAM, max 15 min runtime) as a cost-efficient alternative to ubuntu-latest. However, manually identifying which workflows can safely migrate is tedious and error-prone:

• ❌ Jobs using Docker commands or containers cannot migrate
• ❌ Jobs using services: containers are incompatible
• ❌ Jobs exceeding 15 minutes will fail
• ❌ Container-based GitHub Actions are not supported

gh-slimify automates this entire process, analyzing your workflows and safely migrating eligible jobs with a single command.

Install as a GitHub CLI extension:

Get help:

Scan all workflows in .github/workflows/ to find migration candidates:

Example Output:

The output shows:

• ✅ Safe to migrate: Jobs with no missing commands and known execution time
• ⚠️ Can migrate but requires attention: Jobs with missing commands or unknown execution time
• Warning reasons: Displayed in a single line for easy understanding
• Relative file paths: Clickable links that work in VS Code, iTerm2, and other terminal emulators

Automatically update eligible jobs to use ubuntu-slim. By default, only safe jobs (no missing commands and known execution time) are updated:

Example Output (default - safe jobs only):

To also update jobs with warnings (missing commands or unknown execution time), use the --force flag:

Example Output (with --force):

Scan only specific workflow files:

Skip fetching job durations from GitHub API. This is useful for:

• API rate limit management: Avoid hitting GitHub API rate limits when scanning many workflows
• Faster scans: Skip API calls for quicker results
• When API access is unavailable: Use when GitHub API is not accessible

Use the --verbose flag to enable debug output, which can help troubleshoot issues with API calls or workflow parsing:

Update jobs with warnings (missing commands or unknown execution time):

A job is eligible for migration to ubuntu-slim if all of the following conditions are met:

1. ✅ Runs on ubuntu-latest
2. ✅ Does not use Docker commands (docker build, docker run, docker compose, etc.)
3. ✅ Does not use Docker-based GitHub Actions (e.g., docker/build-push-action, docker/login-action)
4. ✅ Does not use services: containers (PostgreSQL, Redis, MySQL, etc.)
5. ✅ Does not use container: syntax (jobs running inside Docker containers)
6. ✅ Latest workflow run duration is under 15 minutes (checked via GitHub API)
7. ⚠️ Jobs using commands that exist in ubuntu-latest but not in ubuntu-slim (e.g. nvm) will be flagged with warnings but are still eligible for migration. You may need to add setup steps to install these tools in ubuntu-slim.

If any condition is violated, the job will not be migrated.

Jobs are classified into two categories:

• ✅ Safe to migrate: No missing commands and execution time is known
• ⚠️ Can migrate but requires attention: Has missing commands or execution time is unknown

Missing commands are tools that exist in ubuntu-latest but need to be installed in ubuntu-slim (e.g., nvm). These jobs can still be migrated, but you may need to add setup steps to install the required tools.

Result: ✅ Eligible — No Docker, services, or containers

Result: ❌ Not eligible — Uses Docker-based action

Result: ❌ Not eligible — Uses services: containers

Result: ❌ Not eligible — Uses container: syntax

1. Parse Workflows: Scans .github/workflows/*.yml files and parses job definitions
2. Check Criteria: Evaluates each job against migration criteria (Docker, services, containers)
3. Detect Missing Commands: Identifies commands used in jobs that exist in ubuntu-latest but not in ubuntu-slim
4. Fetch Durations: Retrieves latest job execution times from GitHub API (unless --skip-duration is used)
5. Classify Jobs: Separates jobs into "safe" (no warnings) and "requires attention" (has warnings) categories
6. Report Results: Displays eligible jobs grouped by status with:
   • Visual indicators (✅ for safe, ⚠️ for warnings)
   • Warning reasons in a single line
   • Relative file paths with line numbers (clickable in most terminals)
   • Execution durations
7. Auto-Fix (optional): Updates runs-on: ubuntu-latest to runs-on: ubuntu-slim:
   • By default: Only safe jobs are updated
   • With --force: All eligible jobs (including those with warnings) are updated

MIT License