Catch breaking API changes before production.
APIDiffGuard monitors live API responses against versioned baselines, detects JSON schema drift and breaking field changes, and helps teams catch contract breaks before production — with free JSON Diff tools in the browser.
Free for 3 endpoints · no credit card · MIT open source
Cloud reaches public endpoints only. Behind a VPN? Self-host it — same features, MIT.
Built around the diff — not another status board.
Capture baselines, schedule checks, and inspect every field change with the precision of an IDE.
Side-by-side response diff
Collapsible JSON trees, severity-coded changes, path search, and keyboard navigation.
Baselines you trust
Versioned snapshots of status, headers, and body. Approve, restore, and compare any pair.
Scheduled monitoring
Hourly to monthly cadence with request timeouts. Failed runs requeue on the next cron pass.
Alerts that matter
Slack, Discord, Mattermost, email, and webhooks — filtered by severity so noise stays out.
OpenAPI import
Upload JSON or YAML, or paste a URL. Bulk-import endpoints in one pass.
CLI for CI
apidiff check diffs JSON files or a live URL and exits non-zero on breaking changes.
Same engine in the console and in CI.
Review schema drift in the Diff Viewer, or run apidiff check in your pipeline against a baseline file or live URL.
{
"data": {
- "name": "Alex Rivera",
- "id": 4021
}
} {
"data": {
+ "id": "4021",
+ "full_name": "Alex Rivera"
}
}$ apidiff check --baseline users.json --url $API/users
breaking=2 warning=1 info=0
BREAKING removed data.email
BREAKING type_changed data.id
WARNING changed data.role
Failed: 2 change(s) at or above breaking.Open source, and early.
APIDiffGuard is early — we are dogfooding it on our own APIs and iterating from that feedback. Want to share a use case? hello@apidiffguard.com
Baseline → check → diff
Capture a known-good response, re-fetch on a schedule or manually in the console, and review every field change with severity.
Alert when it matters
Route breaking changes to Slack, Discord, Mattermost, or a webhook instead of burying them in log noise.
Same engine as free tools
The browser JSON Diff, Formatter, and Validator use the same comparison engine as the monitored console.
Frequently asked questions
What is schema drift in APIs?
Schema drift is when a live API response changes shape over time — fields disappear, types change, or status classes flip — without your clients being ready. APIDiffGuard detects that by comparing each check to a stored baseline and classifying changes by severity.
How do you detect breaking API changes in CI?
Capture a known-good response as a baseline, re-fetch the same endpoint (or compare JSON fixtures), and fail the job when the JSON diff reports breaking severity. Use apidiff check from @apidiffguard/cli, the console Diff Viewer, or the free JSON Diff tool — they share the same engine.
- Is there a free JSON Diff tool?
- Yes. The free JSON Diff, Formatter, and Validator tools work in the browser without an account. Monitoring live APIs over time is what APIDiffGuard productizes.
- Can I self-host?
- Yes. The project is open-core under MIT. You can self-host, or use APIDiffGuard Cloud so you do not operate auth, databases, and schedules yourself.
Ship APIs with confidence.
Free for 3 endpoints. No credit card. Upgrade when monitoring becomes part of your release ritual.