MockFlow — API Mocking in DevTools

Mock any HTTP response in 3 clicks, right from DevTools. Local-only: no proxy, no mock server, no data leaves your browser.

MockFlow lets you fake any API response straight from Chrome DevTools, without a mock server, proxy or backend changes. Open DevTools, switch to the MockFlow tab, and add a rule: pick a URL pattern, choose a status code, and type the JSON you want back. The page's next fetch or XHR call gets your response instead of the real one. WHAT YOU CAN DO • Return any JSON body for a matching request, edited in a full JSON editor with validation • Override HTTP status codes: test your 401, 404, 429 and 500 handling in seconds • Add delays to simulate slow networks and loading states • Match by exact URL, wildcard or regex, and by HTTP method • Watch matched requests in a live log • Edit rules while the page is open: changes apply without a reload LOCAL-ONLY BY DESIGN MockFlow runs entirely in your browser. Your rules are stored locally, and nothing about the pages you test or the requests you mock is sent anywhere. FREE • 3 active mock rules • 1 profile • Any status code, body and delay PRO: $8/month, or a one-time $29 Founder Pass (limited to the first 100 buyers) • Unlimited active rules and profiles • Custom response headers • Offline / network-failure simulation • Export and import rule sets Buy from the Upgrade button in the MockFlow panel. Payments, tax and receipts are handled by Lemon Squeezy, our Merchant of Record. Pro Monthly can be cancelled anytime. LIMITS MockFlow intercepts the page's own fetch and XMLHttpRequest calls. Web Workers, service workers, image and script loads, navigations, WebSockets and EventSource are not intercepted. Questions or bugs: support@biga.tools