Optimize Runner Usage

Optimize Runner Usage

Scan existing GitHub Actions workflows and add missing runner-usage optimizations: paths-ignore filters, concurrency groups, and timeout-minutes on jobs.

Private GitHub repos pay for Actions minutes, and macOS runners cost 10x Linux runners. These optimizations reduce wasted minutes by skipping unnecessary runs, cancelling superseded builds, and preventing runaway jobs.

Workflow

1. Scan for Workflow Files

Use Glob to find all .yml and .yaml files in .github/workflows/.

If the .github/workflows/ directory does not exist, abort with:

> No .github/workflows/ directory found. This skill optimizes existing GitHub Actions workflows. Invoke the set-up-ci skill to create a CI workflow from scratch.

If no workflow files are found, abort with:

> No workflow files found in .github/workflows/. Invoke the set-up-ci skill to create a CI workflow.

2. Classify Each Workflow

Read each workflow file and classify it based on its on: triggers.

GitHub Actions allows on: in multiple forms:

• Mapping form: on: { push: ..., pull_request: ... } (or multi-line equivalents)
• Single-event shorthand: on: push
• Multi-event shorthand: on: [push, pull_request]

Before classifying, normalize shorthand forms to mapping shape:

• on: push becomes on: { push: {} }
• on: [push, pull_request] becomes on: { push: {}, pull_request: {} }

If applying edits would require rewriting on: from shorthand into a mapping (for example, to add paths-ignore under push:), perform the rewrite explicitly, updating on: to a mapping while preserving existing semantics.

Then classify workflows using the normalized on: structure:

| Trigger pattern | Classification | | ------------------------------------------------------------- | --------------- | | pull_request: (any configuration) | CI | | push: with branches: (optionally plus pull_request:) | CI | | push: with tags: only (no branches: or pull_request:) | Release | | push: with both branches: and tags: | Mixed | | schedule: / workflow_dispatch: only | Scheduled | | Bare push: with no filters | Broad push | | Workflow name or filename contains secret scanning keyword | Secret scanning | | workflow_call: trigger | Reusable |

Secret scanning keywords: "gitleaks", "trufflehog", "secret", "scan" (case-insensitive).

Secret scanning is a subset of Broad push: if a workflow has a bare push: and matches a secret scanning keyword, classify it as Secret scanning rather than Broad push.

For the secret scanning keyword check, inspect in this order:

1. The workflow-level name: field (if present)
2. The workflow filename (without directory path) as a fallback
3. Optionally, job-level name: values as additional signals

Mixed workflows (both branches: and tags: on push) are not eligible for paths-ignore because it cannot be scoped to branch pushes only. They use cancel-in-progress: false for concurrency.

3. Analyze Each Workflow for Missing Optimizations

For each workflow file, check which of the three optimizations are already present and which are needed.

paths-ignore

Eligible: CI workflows only.

Not eligible: Release, Mixed, Scheduled, Secret scanning, Broad push, or Reusable workflows. Also not eligible if the trigger already has a paths: (positive filter), since paths and paths-ignore are mutually exclusive in GitHub Actions. Mixed workflows are excluded because paths-ignore under push: applies to both branch and tag pushes and cannot be scoped to branches only.

Standard paths-ignore list:

paths-ignore:
  - "*.md"
  - "docs/**"
  - "LICENSE"
  - ".editorconfig"
  - ".claude/**"
  - "**/CLAUDE.md"
  - "**/AGENTS.md"

Add paths-ignore under each eligible trigger (push: and pull_request:).

Concurrency

Eligible: All workflow types.

Two concurrency group patterns are used, depending on classification:

Ref-scoped pattern (CI, Scheduled, Broad push, Mixed, Secret scanning, Reusable):

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true # or false, per table below

Workflow-scoped pattern (Release only):

concurrency:
  group: ${{ github.repository }}-${{ github.workflow }}
  cancel-in-progress: false

Release workflows use the workflow-scoped pattern because each tag push produces a unique github.ref (e.g., refs/tags/v1.0.0), so including it in the group never deduplicates concurrent runs. The workflow-scoped pattern serializes all runs of the same release workflow regardless of which tag triggered them.

cancel-in-progress values by classification:

| Classification | cancel-in-progress | Concurrency pattern | | ------------------------- | -------------------- | ------------------- | | CI, Scheduled, Broad push | true | Ref-scoped | | Mixed, Secret scanning | false | Ref-scoped | | Release | false | Workflow-scoped | | Reusable | true | Ref-scoped |

If an existing concurrency group is present but uses a different group: expression than the expected pattern for that classification, flag it for user review. Do not overwrite non-standard concurrency groups automatically.

If an existing concurrency group matches the expected pattern for that classification, check only whether cancel-in-progress needs updating.

timeout-minutes

Eligible: All jobs that lack a timeout-minutes key.

Assign timeouts by heuristic:

| Job indicator | Timeout | | ------------------------------------------------------------- | ------- | | Release, publish, or deploy jobs (by job name or steps) | 30 min | | Rust build jobs (steps contain cargo build or cargo test) | 20 min | | Vuln check, shellcheck, or shell lint jobs | 10 min | | All other CI jobs | 15 min |

4. Present Summary and Confirm

Display a summary table of all workflows with their classifications and proposed changes:

File                        Classification   paths-ignore   concurrency   timeout
ci.yml                      CI               + add          + add         + add (15m)
release.yml                 Release          skip           + add         + add (30m)
gitleaks.yml                Secret scanning  skip           + add         + add (15m)

Use + for additions, skip for not applicable, and a checkmark or note for already present.

Markdown as source code: Before applying paths-ignore to any workflow, ask once whether the project treats Markdown files as source code (e.g., a documentation-focused project where Markdown linting is a CI step). If yes, remove "*.md" from the paths-ignore list for all workflows.

Confirmation: Ask the user to confirm changes for each workflow individually, with options:

1. Apply all: Apply all proposed changes to all workflows
2. Review each: Step through each workflow one at a time
3. Skip: Skip a specific workflow
4. Abort: Stop without making any changes

5. Apply Changes

Use the Edit tool to apply changes. Order within each file:

1. paths-ignore first (under each eligible trigger)
2. Concurrency group second (top-level, after the on: block and before the next top-level key)
3. timeout-minutes third (on each job, after runs-on:)

Preserve existing YAML structure, indentation, and comments. Do not reformat or reorder existing content.

6. Summary

Print a final summary:

• List every modified file and what was added to each
• Note any skipped workflows and why (already optimized, user skipped, flagged for manual review)
• Suggest running CI to verify the changes do not break anything:

> Run your CI pipeline to verify the optimized workflows behave correctly. If any workflow skips when it should run, check the paths-ignore patterns.

Edge Cases

• paths: already present: Do not add paths-ignore (mutually exclusive in GitHub Actions). Note in the summary.
• Existing non-standard concurrency group: Do not overwrite. Flag for the user to review manually. The expected pattern depends on classification: workflow-scoped for Release, ref-scoped for all others.
• Tag-triggered workflows (Release): Use the workflow-scoped concurrency pattern (${{ github.repository }}-${{ github.workflow }}) instead of the ref-scoped pattern, because each tag produces a unique github.ref that never deduplicates. Always use cancel-in-progress: false.
• Mixed triggers (branches + tags on push): Do not add paths-ignore (cannot be scoped to branches only without splitting the workflow). Add concurrency with cancel-in-progress: false and timeout-minutes as normal.
• Already fully optimized: Skip with a note that no changes are needed.
• Reusable workflows (workflow_call:): Skip paths-ignore. Add concurrency and timeouts normally.
• Markdown as source code: User-confirmed. Remove "*.md" from the paths-ignore list.
• Unparseable YAML: Skip the file with a warning and continue with remaining files.

Error Handling

• No .github/workflows/ directory: Abort with a clear message suggesting the set-up-ci skill.
• No workflow files found: Abort with a clear message suggesting the set-up-ci skill.
• YAML parse errors: Skip the individual file with a warning and continue processing other files.
• Empty workflow file: Skip with a note.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: cboone
• Source: cboone/agent-harness-plugins
• License: MIT
• Homepage: https://github.com/cboone/agent-harness-plugins

Install and usage instructions live in the source repository linked above.