OpenAPI Breaking Change Checker

How to use this developer tool

1. Paste a JSON-formatted API document or load the included sample.
2. Check that the document shape matches the label above the editor.
3. Select “Compare Specifications” or press Ctrl/Cmd + Enter.
4. Review the summary and download the copy-ready result.

What this developer tool does

The comparison targets structural removals and stricter parameter requirements that commonly break existing clients.

No findings means this implemented rule set found no break, not that every possible compatibility concern has been proven safe.

Example

The Sample button loads a small specification chosen for this operation. Running it produces the same structured fields shown in the output panel.

{
  "before": {
    "openapi": "3.0.3",
    "info": {
      "title": "Store",
      "version": "1"
    },
    "paths": {
      "/items": {
        "get": {
          "parameters": [
            {
              "name": "limit",
              "in": "query",
              "schema": {
                "type": "integer"
              }
            }
          ],
          "responses": {
            "200": {
              "description": "OK"
            }
          }
        },
        "post": {
          "responses": {
            "201": {
              "description": "Created"
            }
          }
        }
      }
    }
  },
  "after": {
    "openapi": "3.0.3",
    "info": {
      "title": 
…

Use cases

• Review an API contract during a pull request.
• Prepare documentation or deterministic test fixtures.
• Find migration work before changing generators or clients.
• Export a focused report without sharing the source document.

Tips for reliable output

• Bundle remote references before running the page.
• Keep operation IDs stable across published versions.
• Prefer explicit examples for domain-specific values.
• Validate the complete document after applying generated output.
• Commit the original specification before a conversion.

Processing details

Operations are indexed by uppercase method and literal path. Component property removal is checked by schema name and property key without resolving external references.

Schema type narrowing, enum changes, discriminator behavior, request-body constraints, and semantic changes in descriptions are not checked.