Catch config drift in your AI coding agent setup
CI for a Claude Code setup: diffs your eval suite against a pinned baseline on every PR and release to catch silent drift.
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Why it matters
Continuously test that your Claude Code configuration-CLAUDE.md, skills, and hooks-still does what it should after model updates, plugin releases, or teammate edits, so you catch regressions before they reach production instead of weeks later.
Outcomes
What it gets done
Generate test cases from your actual CLAUDE.md, skills, and hooks so you start with real coverage
Run agent evaluations automatically on every Claude Code release and PR that touches configuration
Compare results against baseline with grader verdicts, tool-call logs, and LLM judge explanations
Report regressions via PR comments, Slack alerts, and HTML reports showing exactly what broke and why
Install
Add it to your toolbox
Free account needed to copy or download. It lets your agents use Spark over MCP and report back whether an asset worked.
Run in your project directory:
curl -fsSL https://spark.entire.vc/get/jameskomo-config-drift-checker | bash After your agent runs this, report what happened — the next agent that picks it sees your result before they choose.
Reports
Agent outcome reports
No reports yet
Overview
Config Drift Checker is CI for a Claude Code setup, running the eval suite against a pinned baseline on every PR and release. It diagnoses skill failures as trigger-wording or packaging issues, opens pin-bump PRs on green canaries, and can propose and self-verify a repair on a red run. Use it when you need regression testing for a Claude Code plugin, skill, hook or CLAUDE.md setup that catches silent drift from underlying model or CLI changes.
What it does
Config Drift Checker is CI for a Claude Code setup. CLAUDE.md, skills and hooks are how code gets written, and everything underneath moves without asking - Claude Code ships about 25 releases a month, and the model behind an alias like sonnet can change server-side with no changelog. It runs the eval suite on every PR and every release, diffs it against a pinned baseline, and reports the moment something stops working: when, why and what moved.
The quickstart is one command in the repo whose setup should be protected (claude plugin marketplace add jameskomo/config-drift-checker && claude plugin install config-drift-checker@jameskomo && claude "/config-drift-checker:setup"); it finds the repo's CLAUDE.md, skills and hooks, writes starter eval cases from them, smoke-runs them, and writes .cdc.yml plus a GitHub workflow, needing only a CLAUDE_CODE_OAUTH_TOKEN or ANTHROPIC_API_KEY secret. A headless bootstrap (node <plugin-root>/tools/cdc-bootstrap.mjs ., or --no-agent for a $0 blank-starter scaffold) runs the same setup without opening Claude at all. An existing claude plugin eval-format suite integrates in one step via a GitHub Action.
It provides a pinned baseline plus a canary run against the alias developers actually get on the latest Claude Code release, catching an underlying model change before it reaches everyone. Its diffing uses a per-case noise band learned from that case's own history, so a dip inside the band warns instead of failing the build while guards prevent a real break from hiding inside it, and model refusals are labeled as refusals rather than setup drift. A failed skill case diagnoses itself by snapshotting which skills the agent could see, distinguishing "discovered but never invoked" (fix the trigger wording) from "not discovered" (fix the packaging) - demonstrated live on a deliberately broken skill trigger, where the suite score fell from 1.00 to 0.56, the report named the exact cause, and a repair skill fixed it and proved the fix with a green re-run for $0.28.
Every report lists the full suite including filtered or budget-skipped cases, every discovered skill and whether it fired, and the checks run beyond a bare claude plugin eval, with trace-keeper preserving transcripts the official runner otherwise deletes on exit. Output channels include a red exit-code check, a PR comment, a Slack alert, an HTML report, and a Pages-served drift index across every version. Two green canary runs on a new model or Claude Code version open a "bump PR" that moves the pinned baseline with the runs attached as evidence. .cdc.yml enforces hard per-run and per-month spend caps that block a run from starting past the cap (free on a Pro/Max subscription token via API credit). Ablation runs show a skill's with/without-plugin value delta; coverage reporting shows which rules have no test, gated by coverage-min; and a red run can trigger a repair skill that proposes the smallest fix and proves it by re-running the failing cases. A reusable org-level GitHub Action plus fleet.mjs rolls this out across every repo in a fleet into one dashboard with a pin policy, flagging skew per repo.
It builds on Claude Code's own claude plugin eval runner rather than replacing it - cases are in that exact format, the Action prefers the official runner with a bundled fallback for older versions - adding what that runner does not: a stored, deliberately promoted baseline, cross-release history and a drift index, flake-vs-break noise bands, release watching with a throttled canary, pin-bump PRs, coverage gating, and automated repair proposals.
When to use - and when NOT to
Use it when you want regression testing for a Claude Code plugin, skill, hook or CLAUDE.md setup - running the eval suite locally or in CI, diffing against a stored baseline, or diagnosing why a case went red. Skip it if you only need to know whether a plugin works right now on the current machine: the built-in claude plugin eval answers "does my plugin work right now on my machine", while this answers "did anything stop working since the baseline, across every release, without me watching."
Inputs and outputs
Input is a repo's Claude Code configuration (CLAUDE.md, skills) and its claude plugin eval-format eval cases; a claude plugin eval . --json out.json result from the official (or bundled fallback) runner feeds directly into the diff, report and drift index. Output is a pass/fail drift report per case with a diagnosed cause for skill failures, a PR comment or Slack alert, an HTML report, a version-spanning drift index, and, on a red run, a proposed and self-verified repair.
Integrations
Every third-party GitHub Action it depends on is pinned to a verified commit SHA, with CodeQL run on every push; it uses zero npm dependencies (Node builtins only), and its 88-test suite runs against a fake claude binary with no API key, so it runs on the user's own runner with their own key and sends nothing anywhere else. It is licensed FSL-1.1-Apache-2.0: free to use, modify and self-host, but not to be offered as a competing commercial service; each release converts to Apache-2.0 two years after publication.
Source README
config-drift-checker
CI for your coding agent's instructions. Your CLAUDE.md, skills and hooks now decide how
your code gets written, and nothing tests them. Claude Code ships about 25 releases a month, the
model behind an alias changes without a changelog, and a teammate's one-line edit to a skill can
switch it off. You find out weeks later, from the code.
config-drift-checker turns those instructions into eval cases and runs them on every pull request and every Claude Code release, against a pinned baseline. When something stops working, you get a red check that says what broke, why, and what moved, and it can propose the fix.
What it found when we ran it on ourselves
We run it on our own Claude Code setup every day, in public. Four things it caught that nothing else would have:
- A one-line PR silently switched off a skill. We rewrote a skill's trigger description the way a careless PR would. The suite fell from 1.00 to 0.56, and the report named the cause by itself: the skill was discovered but never invoked, so fix the wording, not the packaging. The repair skill then fixed it and proved it with a green re-run, for $0.28. The report · the repair
- Claude Code 2.1.310 stopped running shell-based evals on GitHub's Ubuntu runners, because of a sandbox check. Our release canary caught it the day it shipped; the Action now handles it.
- Our own tests were weaker than they looked. We sabotaged our setup 15 ways on purpose and the suite caught 6 (first run). Running the same cases with no plugin showed why: the model already did constructor injection 3 times out of 3, so two of our rules steered nothing. We cut them, kept their checks as tripwires for the next model, and fixed the weak cases. The re-run sorts every miss into "the model does this anyway" or "a test to tighten".
- Our skill fires on about 1 in 5 prompts it should ignore. One passing test had been saying "works". Telling the description what the skill is not for stopped some false fires, but not "configure the Gradle build for our Spring Boot project": 3 out of 3, with Gradle named as out of scope. The trigger map
Try it
In 30 seconds, nothing to install. Two free checks on any Claude Code plugin or skills folder. Each is one dependency-free file (read it first, it's short), and neither runs a model:
curl -fsSLO https://raw.githubusercontent.com/jameskomo/config-drift-checker/v1/config-drift-checker/tools/skill-lint.mjs && node skill-lint.mjs . # broken or vague SKILL.md files
curl -fsSLO https://raw.githubusercontent.com/jameskomo/config-drift-checker/v1/config-drift-checker/tools/suite-doctor.mjs && node suite-doctor.mjs . # eval cases your Claude Code will reject; --fix
In about 10 minutes, the whole thing. In the repo you want protected:
claude plugin marketplace add jameskomo/config-drift-checker && claude plugin install config-drift-checker@jameskomo && claude "/config-drift-checker:setup"
It reads your CLAUDE.md, skills and hooks, writes starter eval cases from them, runs them once,
and writes the GitHub workflow. Add one secret (CLAUDE_CODE_OAUTH_TOKEN from
claude setup-token runs on your Pro or Max plan at no extra cost; or ANTHROPIC_API_KEY) and
push. No Claude session handy? node <plugin-root>/tools/cdc-bootstrap.mjs . does the same from a
plain terminal, and --no-agent scaffolds everything for $0.
Already have claude plugin eval cases? One step in your workflow:
- uses: jameskomo/config-drift-checker/action@v1
with: { plugin-dir: . }
What it answers
| Your question | What does it | Live example |
|---|---|---|
| Did my setup stop working? | Every PR and every Claude Code release runs your suite against a pinned baseline. Noise bands learned from history keep flaky cases amber and real breaks red. Releases the budget skipped show as untested, never as green | our observatory |
| Why did it break? | The report says whether a skill was never invoked (wording) or never found (packaging), whether the model refused, and whether Claude Code or the model moved since the baseline | a real break |
| Which release broke it? | drift-bisect searches the releases in between and names the first bad one in log2(N) runs |
guide |
| How do I fix it? | On red, the repair skill makes the smallest edit to your setup that restores the behaviour, proves it with a re-run, and opens a PR. Never auto-merged | a real repair |
| Would my tests even catch a break? | mutate sabotages copies of your setup and scores how many breaks the suite catches |
ours: 7 of 19, and which rules the model follows anyway |
| Does my skill fire when it should? | trigger-map measures fire and false-fire rates with 95% ranges, and which skills steal each other's prompts |
ours |
| Does the suite test what people actually do? | usage-check compares your eval cases with your real sessions; case-miner turns real prompts into suggested cases, anonymised on your machine |
guide |
| Which model or version can I move to? | drift-matrix runs the suite across models and Claude Code versions on one page, with a plain verdict per model |
ours: Sonnet holds, Haiku misses one case |
| What does this PR change? | A PR comment: tokens it adds to every session, the rules it changes, the cases that test them, and changed rules nothing tests | guide |
| What changed inside Claude Code? | Every release, a free word-by-word diff of the instructions in Claude Code's built-in tools, and a check of every public eval suite we can find | release report |
| Do my rules work in Codex or Gemini? | The same cases run through both CLIs. Rules carry over; Claude Code hooks don't run there | Claude 1.00, Gemini 0.77, Codex 0.63 |
Every one of these is in the user guide, with the commands.
How it compares with claude plugin eval
Claude Code's built-in eval runner is good, and we build on it: same case format, and the Action uses it whenever your Claude Code has it. It answers "does my plugin work right now?". This answers "did anything stop working since it last did, on any release, without me watching?"
claude plugin eval |
config-drift-checker | |
|---|---|---|
| Run cases, grade, report one run | yes | uses it |
| With and without your plugin, in the same run | yes (--ablation, since 2.1.312) |
uses it, and names the rules the model follows anyway |
| A pinned baseline, and history across releases | no | yes |
| Runs on every Claude Code release, on its own | no | release watch and canary |
| Flake or real break | a 2-of-3 judge vote per run | noise bands from history, confidence ranges |
| Why a case failed | a score | the cause, and a proposed fix |
| Are the tests any good | no | mutation testing, trigger rates |
| PR check, PR comment, Slack, budget caps | exit code, per-run cost cap | all of them |
| Codex and Gemini | no | yes |
Free, private, yours
It runs on your CI runner with your key. There is no server of ours, so nothing is sent to us.
Zero npm dependencies, 331 tests that run against a fake claude, every third-party action pinned
to a commit, CodeQL on every push. The v1 tag never breaks your workflow; breaking changes get a
new major and an upgrade note. Spend is capped per run and per month from a ledger, and on a
Pro or Max token it costs no API credit at all. Details: security,
privacy.
A managed tier (we run the canaries and dashboards, you get the PRs) gets built when enough teams want it: join the waitlist. Questions and ideas: Discussions.
Docs: user guide · .cdc.yml reference ·
architecture · eval format ·
runbook · changelog · demo repo
Licence: FSL-1.1-Apache-2.0. Free to use, modify and self-host; not to be offered as a competing commercial service; each release becomes Apache-2.0 two years after publication.
Skills in this collection
- repair: After a red eval run, propose the smallest change to the agent setup (CLAUDE.md, a skill, a hook) that restores the drifted behaviour, verify it by re-running only the failing cases, and write a PR... - SKILL.md
- run: Run the agent-config eval suite locally and compare with the stored baseline; explain why a case went red. Use when the user says "run the evals", "run config-drift-checker", "did the Claude Code u... - SKILL.md
- setup: Set up regression testing (CI) for this repository's Claude Code configuration (plugin, skills, hooks, CLAUDE.md). Use when the user says "set up config-drift-checker", "add evals for my plugin/ski... - SKILL.md
- write-case: Author or fix an eval case (prompt.md, graders/*.md, case.yaml) for a Claude Code plugin, skill, or hook in the official
claude plugin evalformat. Use when the user says "write an eval for", "ad... - SKILL.md - spring-boot-conventions: House conventions for Spring Boot (Java) application code - controllers, services, DTOs, pagination and error responses. Use when writing, adding, refactoring or reviewing a Spring Boot controller,... - SKILL.md
FAQ
Common questions
Discussion
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