API Breaking Change Detector
Detect breaking and non-breaking OpenAPI changes before they reach production, with rules that account for request and response context. Runs in CI, in your terminal, or in the browser.
What Are Breaking API Changes?
A breaking change is any modification to an API that causes existing clients to fail. Removing an endpoint, changing a field type from string to integer, or adding a new required parameter — these all break clients that rely on the previous contract.
Breaking changes in production cause outages, support tickets, and lost trust. Delimit catches them at the pull request stage — before merge, before deploy, before anyone notices.
Breaking change types (examples)
| Type | Description | Severity |
|---|---|---|
| endpoint_removed | An API endpoint was removed entirely | high |
| method_removed | An HTTP method (GET, POST, etc.) was removed from an endpoint | high |
| required_param_added | A new required parameter was added to an operation | high |
| param_removed | A parameter was removed from an operation | high |
| response_removed | A response status code was removed | high |
| required_field_added | A new required field was added to a request body | high |
| field_removed | A field was removed from a response schema | high |
| type_changed | A schema property type was changed (e.g., string to integer) | high |
| format_changed | A schema property format was changed (e.g., int32 to int64) | medium |
| enum_value_removed | An allowed enum value was removed | high |
| param_type_changed | A parameter type was changed | high |
| param_required_changed | A parameter changed from optional to required | high |
| response_type_changed | A response schema type was changed | high |
| security_removed | A security requirement was removed | medium |
| security_scope_removed | An OAuth scope was removed from a security requirement | medium |
| max_length_decreased | A maxLength constraint was made more restrictive | medium |
| min_length_increased | A minLength constraint was made more restrictive | medium |
10 Non-Breaking Change Types
| Type | Description |
|---|---|
| endpoint_added | A new API endpoint was added |
| method_added | A new HTTP method was added to an endpoint |
| optional_param_added | A new optional parameter was added |
| response_added | A new response status code was added |
| optional_field_added | A new optional field was added to a schema |
| enum_value_added | A new enum value was added |
| description_changed | A description or summary was updated |
| security_added | A new security requirement was added |
| deprecated_added | A deprecation marker was added |
| default_changed | A default value was changed |
How to Detect Breaking Changes
GitHub Action
Runs on every PR. Posts a comment with all detected changes, severity grades, and migration steps. Blocks merge on breaking changes.
CLI
Run locally or in any CI pipeline. Returns exit code 1 on policy violation so you can gate deployments.
Playground
Paste two specs in the browser. No install, no account. See results instantly with severity badges and migration guides.
Open Playground →Stop Shipping Breaking Changes
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