API Diff - Response Change Detector

Detect API response changes, compare JSON contracts, save baselines, view history, and export diffs from Chrome DevTools.

API Diff is a Chrome DevTools extension for developers who need a simple way to detect changes in JSON API responses. Instead of manually comparing API responses, API Diff automatically captures JSON Fetch/XHR responses while Chrome DevTools is open and keeps a local response history. Key Features • Automatic JSON API response capture from Chrome DevTools • Contract Mode for detecting API schema changes • Values Mode for comparing response values • Detect added and removed fields • Detect data type changes • Detect required/optional field changes • Improved contract detection for arrays • Save a known response as a baseline • Compare future responses against your baseline • Keep recent response history • Ignore noisy fields such as timestamps and request IDs • Search captured APIs • Filter APIs with detected changes • Copy diff reports to the clipboard • Export diff reports as text files Contract Mode focuses on API structure instead of normal data changes. For example, changing a field from a number to a string is detected as a contract change, while ordinary value changes are ignored when the field type remains unchanged. Save a working API response as your baseline. When the API is called again, API Diff compares the latest response against the saved baseline, making it easier to notice unexpected backend changes. API Diff processes API responses locally in your browser. Captured history, baselines, and ignore-field settings are stored using Chrome's local extension storage. API Diff does not send captured API responses to an external server and does not use analytics or advertising services. Designed for frontend developers, backend developers, QA engineers, API testers, and teams working with JSON APIs.