TheOneX Mock – API Mocking for REST & GraphQL

Mock API responses, rewrite requests and modify headers for REST and GraphQL.

TheOneX Mock lets developers and QA engineers control what an API returns, straight from the browser — no proxy, no code changes, no backend work. WHAT YOU CAN DO - Mock responses – return any status code (200, 400, 404, 500…), headers and body for a matching call, with an optional delay to simulate a slow network. - Modify requests – send a call to a different URL, or replace or merge the JSON body before it leaves the browser. - Modify headers – set or remove request and response headers. REST AND GRAPHQL - Match REST calls by URL (contains, equals, wildcard or regex) and HTTP method. - Match GraphQL calls by operation name, operation type (query or mutation) or query text — so you can mock one operation while every other call to the same /graphql endpoint stays real. - Override GraphQL variables by merging JSON into the request. SEE MOCKS IN THE DEVTOOLS NETWORK TAB Set a mock to "Visible in Network tab" and the call appears in DevTools with your mocked status and body, like a real response. Useful for capturing evidence of how the UI behaves on a 500 or an empty result. This mode is optional: Chrome asks for the debugger permission only when you switch it on, and shows a "started debugging this browser" banner while it is in use. BUILT FOR TESTING - Turn all rules on or off with one switch, or toggle rules individually from the toolbar popup. - Activity log shows which calls each rule was applied to. - Import and export rules as JSON to share them with your team. - Rule changes apply immediately — no page reload. - Mocked responses carry an "x-mocked-by: TheOneX Mock" header so they are never mistaken for real ones. PRIVACY TheOneX Mock has no server and no analytics. Your rules are stored only in your own browser. Nothing is collected or sent anywhere. LIMITS Mocking and request rewriting apply to fetch and XMLHttpRequest calls made by pages and iframes. Calls made from service workers or web workers, page navigations and WebSocket messages are not intercepted.