Mockfly is a mock API service for developers who need a working endpoint before the real one exists.
Almost every screen you build depends on an API that isn't ready. The backend team is still arguing about the shape of the response, the third-party provider hands you sandbox credentials that expire, and the error case you actually need to handle only ever happens in production. So the frontend either waits, or it gets built against hardcoded fixtures that quietly drift away from reality and have to be ripped out later.
Mockfly removes that wait. You describe an endpoint — path, method, status code, headers, response body — and you get a real HTTPS URL that answers immediately. Your app talks to it exactly the way it will talk to the real service, so when the real service finally ships, you change a base URL and move on.
Everything happens in the browser, with nothing to install. Each endpoint can hold several responses, so you can flip between the happy path, a 500 and an empty list while you build the UI. Conditional rules pick the response based on what the incoming request contains. Faker.js templating and AI-generated JSON keep the payloads looking like real data instead of test test test.
On top of that there are dynamic routes, custom headers and status codes, XML as well as JSON, file responses such as PDF and CSV, WebSocket mocking, request logs, and documentation generated from the endpoints you already defined. A Chrome extension captures calls against a real API and turns them into mocks, and the mockfly-cli npm package pulls your projects down so they keep serving with no internet at all — on a plane, or inside CI.
Mockfly was started in 2023 by Sergio Zamarro and is built by a small independent team of developers. It is self-funded: there are no investors to satisfy, which is why the free plan is genuinely free and the paid plan costs 8€ a month flat instead of being priced per seat.
There is no ticket queue between you and us. Write to [email protected] and one of the people who writes the code answers, in English or Spanish. Feature requests land in the same inbox and reach the same people — see contact for what to expect.
More than 5,000 developers use Mockfly, from two-person startups to engineering teams inside large companies — the logos on the home page are theirs. The free Starter plan gives you 500 requests a day, one project with four endpoints and two responses per endpoint, and asks for no credit card. Professional lifts every one of those limits for 8€ a month or 88€ a year, and teams that need seats, centralised billing and priority support are on the Company plan. The full breakdown is on pricing.
Alongside the product we run the API Hub: a set of free public mock APIs — users, products, posts, comments, albums, photos, todos — that anyone can call without signing up, for demos, tutorials and throwaway prototypes.
Mockfly stores the mock definitions you create and the request logs of your own projects, and uses them for nothing except running the service. We don't sell that data and we don't set tracking cookies. The detail, including how to ask for your data to be exported or deleted, is in the privacy policy.
Or skip the reading and create a mock API — the free plan needs no card.