github-codespaces-efficiency

# GitHub Codespaces Efficiency Use this skill as a lean entrypoint for GitHub Codespaces efficiency work. Inspect the repo, identify waste, and load only needed references. If no `.devcontainer/` exists yet, load [`references/codespaces.md`](./references/codespaces.md) and define a baseline before proceeding with the steps below. ## Use This Skill When - The user wants faster Codespaces startup or lower Codespaces spend. - The repo has a `.devcontainer/` or explicit Codespaces configuration questions. - The user asks for devcontainer optimization, machine sizing, prebuild strategy, or idle-timeout guidance. - The user is setting up Codespaces for the first time or needs help creating a new `.devcontainer/` from scratch. ## Load Only What You Need - [`references/codespaces.md`](./references/codespaces.md) — devcontainer, machine-sizing, prebuild, idle-timeout guidance, and reporting. - [`references/review-rubric.md`](./references/review-rubric.md) — load only for review passes. ## Core Workflow ### 1. Measure first ```bash find .devcontainer -maxdepth 2 -type f gh codespace list repo=$(gh repo view --json nameWithOwner --jq .nameWithOwner) gh api "/repos/$repo/codespaces/machines" ``` If `gh` auth fails or the user lacks repo admin scope, proceed with static analysis of `.devcontainer/` files; mark machine-type and prebuild recommendations as unverified. Look for: devcontainer image >2 GB or more than 10 features, machine type larger than usage data supports, missing `devcontainer-lock.json` (recommend adding — many repos predate lock-file support), prebuilds scoped too broadly, and idle timeout mismatched to usage patterns. ### 2. Apply guardrails Check each proposed fix against these rules before recommending it: 1. Does not remove tools the team uses every day — drop any fix that strips required development tools or extensions. 2. Does not assume smaller is always better — balance machine cost against developer experience and throughput. 3. Does not turn the devcontainer into a production image — drop any fix that adds production-only dependencies unless the team explicitly requires it. 4. Incremental changes preferred — a greenfield baseline is appropriate only when no `.devcontainer/` exists; flag (do not drop) changes that restructure an existing config. 5. Repo changes stay separate from org settings — split any fix that mixes repo-editable files with org-level or user-level Codespaces settings into two distinct recommendations. ### 3. Select the top 3 fixes From the six candidates below, keep only those supported by audit evidence from step 1 *and* passing all guardrails from step 2. Rank survivors by estimated monthly cost savings (USD). Select all candidates that meet both criteria, up to a maximum of 3. 1. Trim devcontainer — remove features, packages, or extensions not needed for everyday development work; target image <2 GB and fewer than 10 features 2. Right-size machine type — match to observed usage patterns; if data is unavailable, state assumptions explicitly 3. Scope prebuilds — enable for the default branch, `release/*` branches active in the last 14 days, and branches with more than 5 Codespaces per week; disable for all others 4. Tune idle timeout — 30 min default; 15 min if most sessions end before 30 min; 60 min if most sessions run longer 5. Remove unused extensions or port-forwarding rules 6. Reduce devcontainer image size and improve layer caching ### 4. Verify - Start a test Codespace to confirm devcontainer changes build and start as expected. - Validate machine sizing against observed usage when telemetry is available; otherwise mark as unverified. - Treat unexpected build or startup failures as real bugs even when the configuration looks correct. ## Required Output **Waste sources:** [top cost or startup-time drivers] **Proposed fixes:** [top 3 changes supported by audit evidence and passing guardrails] **Validation:** [proven live / static-only / remaining risk] **Impact:** - Startup time: [expected] / [measured if available] - Monthly spend: [expected] / [measured if available] - Resource utilization: [expected] / [measured if available] ## References - [`references/codespaces.md`](./references/codespaces.md) - [`references/review-rubric.md`](./references/review-rubric.md) — load when reviewing completed efficiency work