API Response Time Machine

About

API Response Time Machine records every JSON API response your browser makes — across sessions, across days — so you can replay history, diff two versions side-by-side, and detect when a response silently changed shape.

WHAT IT DOES

Every fetch() and XMLHttpRequest is intercepted and stored locally. For each response you get: the full response body, the request body (for POST/PUT/PATCH), request and response headers, HTTP status code, and a structural schema automatically derived from the JSON.

The shape detection is the core feature: the extension computes a hash of each response's structure (not its values). When the same endpoint returns a response with a different structure — even days later — it is automatically flagged in the Changes tab and recorded in the Shape History timeline. You do not need to be watching.

TABS

Feed — a live-updating list of every captured API call. Filter by URL, method, or search term. Click any record to inspect the full body, request payload, shape, and headers.

Changes — every endpoint where the response structure changed between calls. Click any entry to jump straight to a pre-loaded diff.

History — a per-endpoint shape timeline. See every distinct structure an endpoint has ever returned, when it changed, and what changed. "Diff vs prev" loads the comparison instantly.

Diff — LCS-based line diff between any two captured records. Works in both Shape mode (structural comparison) and Body mode (full JSON comparison).

Settings — include/exclude filters with plain text, glob wildcards, and full /regex/ support. Export all records as JSON or HAR (compatible with Chrome DevTools, Postman, Insomnia). Import records from a previous export. Toggle shape change browser notifications.

PRIVACY

Everything stays on your device. All data is stored in chrome.storage.local — nothing is ever sent to any server. The extension makes zero outbound network requests.

WHO IT IS FOR

— Frontend developers debugging why the UI broke after a backend deploy
— QA engineers monitoring third-party APIs for silent breaking changes  
— Backend developers verifying their API contracts haven't drifted
— Anyone who has ever asked "wait, did this API change?"