API Override

API Override is a developer tool for intercepting and modifying network requests in the browser. Build a list of rules, toggle them on or off individually, and reshape traffic without touching your application code. ━━━━━━━━━━━━━━━━━━ What's New ━━━━━━━━━━━━━━━━━━ v1.2.0 You can now duplicate a rule with one click — handy for tweaking a near-identical variant without re-entering every field from scratch. Regex fields (Redirect, Query Param, and Modify Response URL patterns) also got a Build regex helper: a modal with common pattern snippets (path segments, digits, capture groups, and more) plus a live tester so you can check a sample URL against your pattern before saving. v1.1.0 Export & Import rules. Move your rules between computers. Pick exactly which rules to export (select all or choose individually) and save them to a file; import that file on another machine. Smart duplicate detection on import. Rules that match ones you already have are skipped automatically, so you won't end up with duplicates. The comparison looks at each rule's settings, not its name — renamed copies are still caught. Safe imports. Imported rules always arrive disabled, so nothing takes effect until you review and switch them on. Import report. After importing you get a clear summary of which rules were added and which were ignored (and why). v1.0.1 Full visual redesign with a cleaner, more consistent interface across the popup, options, and help pages. Redirect rules now forward all headers from the original request to the target — including Authorization and cookies across origins — so redirecting to a local or staging API "just works." Popup rules restyled as cards to match the options page. v1.0.0 Initial release. Redirect requests, replace strings in URLs, add/replace/remove query parameters, and mock API responses — all with an ordered, individually-toggleable rule list and a master on/off switch ━━━━━━━━━━━━━━━━━━ What you can do ━━━━━━━━━━━━━━━━━━ ▸ Redirect Request — match a URL with a regular expression and send it somewhere else. Capture groups in the match (\1, \2, …) are usable in the target. Perfect for pointing a production API at a local dev server, or swapping one CDN for another. ▸ Replace String — plain find-and-replace inside the URL, no regex needed. Quick way to swap a hostname, force HTTPS, or change an API version. ▸ Query Param — add, replace, or remove a query parameter on matching requests. Useful for injecting debug flags, stripping tracking parameters (utm_*), or appending a cache-buster. ▸ Modify Response — return a custom status code, content-type, and body for matching requests. The request never hits the real server. Great for mocking an unbuilt endpoint, simulating a 500 error to test failure paths, or stubbing out analytics calls with an empty 204. ━━━━━━━━━━━━━━━━━━ Why you'd want it ━━━━━━━━━━━━━━━━━━ • Front-end work against an API that isn't ready yet — mock it. • Reproduce a bug that only happens when an endpoint returns a specific error. • Demo or QA a build against a different backend without rebuilding the bundle. • Strip tracking parameters from the URLs you click. • Test how your app behaves when a third-party script fails to load. ━━━━━━━━━━━━━━━━━━ How it works ━━━━━━━━━━━━━━━━━━ Redirect, Replace String, and Query Param rules run on Chrome's native declarativeNetRequest engine — fast, and they don't read the contents of any request. Modify Response rules use the Chrome DevTools Protocol (the "debugger" permission) because that is the only API capable of substituting a response body in Manifest V3. While at least one Modify Response rule is enabled, Chrome shows its standard "this browser is being debugged" notice. Disable or delete those rules (or flip the master toggle off) and the notice disappears immediately. A master switch in the popup turns everything off without losing your rules. Each rule also has its own enable/disable toggle. Rules apply top-to-bottom; conflicting rules are resolved by list order. Changes save automatically. ━━━━━━━━━━━━━━━━━━ Privacy ━━━━━━━━━━━━━━━━━━ API Override does not collect, transmit, or store any browsing data on remote servers. Your rules are saved locally in Chrome's extension storage, on your machine. Nothing leaves the browser.