The OpenAPI Spec Changelog Generator uses the oasdiff library (Go-based OpenAPI diff engine) to perform deep semantic comparison between two versions of OpenAPI 3.x specifications. Unlike simple text diffs, it understands OpenAPI structure to detect breaking changes (removed endpoints, required parameter additions, response schema narrowing), non-breaking additions (new optional parameters, additional response fields), and deprecations. The skill parses both YAML and JSON spec formats and resolves $ref references across multi-file specifications. It classifies changes by severity level following the OpenAPI breaking change taxonomy and generates human-readable changelogs in Markdown format suitable for developer portal publication, or structured JSON for integration with API governance pipelines. The generator supports comparing specs from URLs (pulling from Swagger Hub or API gateway exports) and can be integrated into CI to block PRs that introduce unannounced breaking changes.