diff-specs

Diff Two OpenAPI Specifications

Step 1: Compare the specs

⚠️ Note: The diff tool is designed for comparing versions of the same API (e.g., v1.2 vs v1.3). Diffing unrelated APIs (e.g., Stripe vs GitHub) will produce thousands of changes that aren't meaningful. If the user wants to compare different APIs, suggest exploring each one separately with the explore-api workflow.

Call the diff tool with both spec versions:

{
  "base": {"file": "<old-version-path>"},
  "revision": {"file": "<new-version-path>"}
}

To focus only on breaking changes:

{
  "base": {"file": "<old-version-path>"},
  "revision": {"file": "<new-version-path>"},
  "breaking_only": true
}

Step 2: Categorize changes

Paginating large diffs

Results are paginated (default limit: 100). When returned < total_changes, there are more changes:

{
  "base": {"file": "<old-version-path>"},
  "revision": {"file": "<new-version-path>"},
  "offset": 100, "limit": 100
}

⚠️ Strategy for large diffs: Start with breaking_only: true to see all breaking changes first — these are usually the most important and fewest. Then page through the full diff only if the user needs the complete picture. The total_changes, breaking_count, warning_count, and info_count fields always reflect the full result, even when paginated.

Present the diff results organized by severity:

1. Breaking (critical/error) -- Changes that will break existing API consumers

   • Removed endpoints or operations
   • Removed or renamed required parameters
   • Changed response status codes
   • Narrowed allowed values (enum removals, stricter validation)
   • Changed authentication requirements

2. Warnings -- Changes that may affect consumers

   • Deprecated endpoints
   • Changed optional parameter defaults
   • Modified response schemas (new required fields)

3. Informational -- Non-breaking changes

   • Added endpoints or operations
   • Added optional parameters
   • Extended enum values
   • Documentation updates

Step 3: Explain breaking changes

For each breaking change:

• Describe what changed (the specific path and property)
• Explain why it breaks consumers (e.g., "Clients sending requests to DELETE /users/{id} will get 404")
• Estimate the scope of impact (how many operations/schemas are affected)

Step 4: Suggest migration path

For each breaking change, provide a concrete migration step:

Change type	Migration guidance
Removed endpoint	Update client to use the replacement endpoint (if one exists)
Removed parameter	Remove the parameter from requests; check if behavior changed
Type change	Update request/response handling for the new type
Auth change	Update authentication configuration
Renamed field	Update all references to use the new name

Step 5: Summary

Provide a migration checklist:

• Total changes (breaking / warning / info)
• List of required client-side updates
• Recommended testing strategy for the migration
• Whether the version bump follows semver conventions (breaking changes = major bump)