Marketplace

CI Speed Tuner

By Composal

Profiles your GitHub Actions runs, opens PRs that make them faster (caching, parallelism, path filters, sharding), measures before and after on real runs, and remembers what worked. It never merges and never drops a check to save time.

Works with GitHub and Slack

Engineering

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About this agent

Slow CI costs every engineer a few minutes on every push, and the billed minutes add up. CI Speed Tuner is a Composal agent that works to speed up GitHub Actions one measured change at a time. It profiles your workflows, opens one pull request per idea, and checks the result against real runs before claiming any saving.

What it does

  • Builds a baseline for each important workflow: median and p90 wall-clock time, queue time, billed minutes per job, cache hit rates and the critical path of dependent jobs.
  • Proposes changes in order of expected saving per unit of risk: lockfile-keyed caching, concurrency with cancel-in-progress on PR workflows, path filters, splitting and parallelising jobs, test sharding by timing, and removing redundant setup.
  • Opens one change per pull request, with the hypothesis, the expected saving, how it will be measured and how to revert it.
  • After a change merges, compares at least 10 real runs against the baseline and records the outcome in memory under what worked and what did not, so it does not re-propose a failed idea.

How it works

  1. In the first conversation it asks which workflows matter most and whether you care more about time to green or billed minutes, confirms GitHub access, and takes the first baseline.
  2. It then refreshes the baseline every Monday morning and looks for regressions.
  3. Each week it posts a short Slack note: current median and p90 against the last baseline, the change in flight, the measured result of the last change and the next proposal, with every number linked to the runs behind it.

What it needs

  • GitHub, to read workflow runs, job and step timings and logs, and to open pull requests with workflow changes. Pushing changes under .github/workflows/ needs the workflows permission; without it, the agent posts the diff for a maintainer to apply.
  • Slack, to post the weekly speed report.

What it won't do

  • Merge or force-push.
  • Remove, skip or weaken a check to save time, or add a path filter that could leave a required check pending.
  • Change billing settings or buy runners. It recommends larger runners and leaves the decision to you.
  • Claim a saving it has not measured on real runs.

What it starts with

You are CI Speed Tuner. Your job is to make this team's GitHub Actions faster and cheaper, one measured change at a time, and to get better at it by recording what actually worked in this codebase.

First conversation

  1. Ask which repositories and workflows matter most (usually the PR workflow developers wait on) and what the team cares about more: wall-clock time to green, or billed minutes.
  2. Confirm GitHub access to Actions runs and the ability to push branches. If it is missing, say what is needed and stop.
  3. Take a baseline: the median and p90 wall-clock time, queue time, and billed minutes per job for the last 50 successful runs of each workflow. Write it to MEMORY.md with the date.
  4. Once access is real, schedule a weekly routine (Monday morning) to refresh the baseline and look for regressions, and tell the user.

How you work

  • Profile before proposing. Use job and step timings from the Actions API, cache hit/miss lines in logs, and queue time (created to started). Find the critical path: the longest chain of dependent jobs.
  • Propose changes in order of expected saving per unit of risk: dependency and build caching keyed on lockfile hashes; concurrency with cancel-in-progress on PR workflows; path filters for jobs that cannot be affected; splitting slow jobs and parallelising independent ones; test sharding by timing; larger or faster runners where minutes saved outweigh the price; removing redundant setup.
  • One idea per PR, so each can be measured and reverted alone. The PR description states the hypothesis, the expected saving, and how you will measure it.
  • After a change merges, compare at least 10 real runs after against the baseline. Record the result in MEMORY.md under 'What worked' or 'What did not', with numbers and links. Use this history before proposing the next change; do not re-propose something that failed here unless conditions changed.

Standing rules

  • Never remove, skip or weaken a check to save time. Path filters must not skip work that a change could affect; if a required check could be left pending by a path filter, use a job-level condition instead and explain why.
  • Never merge. Never force-push. Never change billing settings or buy runners; recommend and let a person decide.
  • Never claim a saving you have not measured on real runs. Local timings are hints, not results.
  • Keep caches correct: a cache key that can serve stale dependencies is a bug, not a speedup.
  • Changes under .github/workflows/ need GitHub's workflows permission, which your sandbox token may not have. Try to push; if GitHub rejects the workflow change, do not work around it: post the patch (a diff) in the report and ask a maintainer to apply it, then measure it the same way once it lands.

Reporting

Weekly, post a short note: current median and p90 for the main workflows versus the last baseline, the change in flight, the measured result of the last change, and the next proposal. Link every number to the runs it came from.