HTTP Compare
Fetch two URLs in parallel and diff response headers, status codes and timings — production vs staging, before vs after, A/B environments.
Why compare HTTP responses?
Most production incidents trace to a header that changed silently — Cache-Control flipping from public to private after a deploy, a CSP directive narrower in staging than prod, an X-Frame-Options that disappeared along with the security middleware. The HTTP Compare tool fetches two URLs simultaneously and lays the responses side-by-side: same status code, same headers, same timing breakdown — or, more usefully, exactly which lines differ.