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Protonosis

Diagnose your API before your users do.

Inconsistent naming, misused status codes, semantic drift, and design smells that style linters can't catch — found before they reach your consumers.

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diagnosis.log — openapi.yaml
$ protonosis scan openapi.yaml
 
Scanning 42 endpoints across 8 resources...
 
BREAKING `GET /users/{id}` — field `email` removed from response
BREAKING `POST /orders` — `quantity` changed from string to integer
WARNING  `GET /users` returns object. `GET /orders` returns array. Inconsistent.
WARNING  `GET /invoices` — returns 200 on error; convention elsewhere is 4xx
 
─────────────────────────────────────────────
2 breaking changes · 2 warnings · 3 suggestions

The bugs your linter never finds.

GET /users returns an object. GET /orders returns an array. Nobody noticed until the SDK broke.

That endpoint returns 200 with {"{"}"error": ...{"}"} in the body. Your consumers' retry logic never fires.

Someone renamed a field in a "minor" PR. Three downstream services broke on Friday.

Style linters check your commas. Protonosis checks your meaning.

Three steps. One diagnosis.

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Get a diagnosis

Semantic issues, design inconsistencies, and REST anti-patterns — each with severity and a suggested fix.

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Send a link to your team or drop it in the PR. The shareable report is built-in.

What a real diagnosis looks like.

protonosis-report.txt — stripe-api-v3.yaml
Protonosis Diagnostic Report — stripe-api-v3.yaml
BREAKING CHANGES (2)
  • BREAKING `GET /customers/{id}` — field `metadata` removed from response schema
  • BREAKING `POST /charges` — `currency` changed from optional to required
SEMANTIC WARNINGS (3)
  • WARNING `DELETE /subscriptions/{id}` returns 200; convention elsewhere is 204
  • WARNING `GET /invoices` — response shape differs from `GET /invoices/{id}`
  • WARNING `POST /refunds` — missing 409 conflict response for duplicate refund
SUGGESTIONS (2)
  • Consider paginating `GET /events` — unbounded array response
  • `customerId` and `customer_id` used interchangeably across resources

Catch breaking changes before they ship.

Add Protonosis to your CI pipeline and every PR that touches your API contract gets diagnosed automatically.

Breaking-change detection

Removed fields, changed types, narrowed enums, altered status codes. Flagged before merge, not after the incident.

Semantic drift alerts

New endpoints that break your API's existing conventions are caught automatically.

PR comments, not dashboards

Findings show up where developers already work — inline in the pull request.

protonosis-ci commented on this PR
❌ protonosis: 2 breaking changes detected in openapi.yaml
 
BREAKING `GET /users/{id}` — field `email` removed from response
BREAKING `POST /orders` — `quantity` changed from string to integer
WARNING  `GET /invoices` — returns 200 on error; convention elsewhere is 4xx
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