Mocktail: Mock API & Modify Requests

Intercept and mock API responses, override JSON, status codes, and headers. Modify requests locally, open source.

Mocktail helps you mock APIs right in the browser — so you can shape responses, tweak outgoing requests, and ship UI faster without waiting on the backend. Own the response Set status, delay, body, and headers. Empty lists, 500s, slow networks — on demand, whenever you need them. Capture, then mock Inspect real traffic in Requests and turn any call into a rule in one click. Shape the request Inject headers or add delay before send and keep the real response when you only need the request changed. Built for everyday frontend work Prototype before the API exists with realistic JSON, status codes, and timing. Exercise the hard paths: empty states, auth failures, timeouts, flaky networks. Enable mocking on a single tab so everything else stays untouched. Organize with rule sets, switch contexts, import and export JSON, or draft rules with an AI-friendly prompt helper. Work in a side panel that stays open next to your page while you iterate. How it works When you start mocking on a tab, Mocktail evaluates your enabled rules from top to bottom. A rule matches on URL and HTTP method. Response mode intercepts and fulfills with your status, body, headers, and delay. Request mode keeps the real response and merges headers into the outgoing request. Unmatched traffic passes through as usual. Mocking stays off until you explicitly enable it for a tab. Private by design, open by nature Rules, settings, and request history stay on your machine. Mocktail is open source under the MIT license — inspect the code, suggest improvements, or build it yourself. Your traffic never leaves your browser.