OpenAPI and JSON Schema breaking change checker.

Online OpenAPI and JSON Schema compatibility checks

Use this free API compatibility checker to understand how a contract change affects existing integrations. Replay a captured OpenAPI finding from OpenAI or Sentry, inspect its classification rule, or compare a pair of JSON Schemas. The examples run without an account or repository access. Each result separates contract evidence from the question of whether your application uses the affected operation.

• Request narrowing

  The revised request schema must accept the inputs existing callers could send. Increasing a minimum, decreasing a maximum, or tightening a string constraint can reject previously valid requests. Check the affected field and the acceptance direction.

• Enum value removal

  Removing a request enum value leaves callers using that value outside the new contract. Inspect where the value is selected before choosing an alternative; the specification finding does not invent a replacement for your application.

  Recorded rule: request.enum_removed

• Required request field addition

  Adding a required property, or making an optional request field required, can reject older payloads that omit it. A compatible migration needs an appropriate application value, not simply a placeholder added to satisfy the schema.

• Response widening

  Existing consumers must handle the outputs allowed by the revised response. A field becoming optional or nullable, a new enum value, or a broader type can invalidate assumptions in parsing, branching, and typed response handling.

  Recorded rule: response.now_optional_or_nullable

The JSON Schema comparison checks directional acceptance and reports equivalent, different, or undetermined. A validated counterexample demonstrates a specific difference; unsupported constructs or missing proof remain undetermined. OpenAPI detector findings have their own recorded classification rules. Schema comparison is not a complete OpenAPI upload diff or proof of repository impact. Use public or illustrative schemas, inspect the evidence, and run your own CI before merging.

Explore API specification history · Contract and repository coverage