Mockoon

Mockoon is a free, open-source API mocking suite — desktop app, CLI, serverless package, and now a paid Cloud — that lets you spin up a fully working mock REST API in under a minute, with no account, no deployment, and no internet connection required. We rate it 88/100 — it is the easiest tool we've tested for the everyday job of "I need a fake API to develop against, right now," and the only one in its tier that runs entirely offline.

What is Mockoon?

Mockoon was created by Guillaume Tognoni-Ostre (handle @255kb) and first released as an open-source Electron app on July 17, 2017. It is licensed under MIT, the GitHub repository at github.com/mockoon/mockoon currently has 8,227 stars and 460 forks, and the latest stable release as of April 27, 2026 is v9.6.1 (shipped April 2, 2026). Mockoon is also a GitHub Accelerator alum and is proudly built and operated in the European Union.

The product solves a very specific developer pain: you have a frontend or mobile app under construction, the real backend isn't ready, and you don't want to write yet another Express stub or pay for a SaaS just to fake a few endpoints. Mockoon lets you click a route into existence, paste in a JSON body, hit a switch, and have a real HTTP server listening locally — all inside a desktop window that does not phone home.

Key Features of Mockoon

• Sub-minute setup: the desktop app installs in under 30 seconds on Windows, macOS, and Linux. Creating a working GET /users mock with a JSON body takes 4 clicks.
• OpenAPI import & export: drop in any OpenAPI 3.0 / Swagger 2.0 spec and Mockoon generates routes for every operation. Round-trip back out as YAML or JSON for your real API repo.
• Dynamic templating with Faker.js + Handlebars: generate realistic random data per request — names, UUIDs, locales, geolocation, prices — without any custom code.
• Rules matching: route a single endpoint to different responses based on body, query, header, or cookie matchers. This makes happy-path / error-path testing trivial.
• Stateful CRUD with JSON databases: attach a JSON file as a data store and Mockoon will handle GET/POST/PUT/PATCH/DELETE with persistent state — perfect for prototyping a full CRUD UI.
• Proxy mode & request recording: point Mockoon at a real upstream, capture every call your app makes, and auto-generate mocks from the recordings. This is how you stub out a partner API you don't fully control.
• Mockoon CLI & Docker image: the same environment runs headless in CI — GitHub Actions, CircleCI, GitLab — with one Docker line: docker run -p 3000:3000 mockoon/cli.
• Serverless package: deploy your Mockoon environment as an AWS Lambda, GCP Function, or Firebase Function with a tiny Node wrapper.
• AI-powered endpoint generation (Cloud): describe an API in plain English and Mockoon Cloud generates routes, JSON schemas, and example responses. The Solo plan includes 100 AI endpoints/month; Team includes 200/user/month.

What Users Say About Mockoon

Mockoon scores 4.5/5 on G2 and 4.5/5 on Capterra, with a 5/5 average on Product Hunt. Reviewers consistently praise three things: the speed of getting a mock running ("under a minute" is the most-quoted phrase across reviews), the offline-first stance — meaning you can use it on a plane, behind a corporate firewall, or in an air-gapped environment — and the depth of the rules and templating engine compared to free alternatives.

The recurring complaints are equally clear. The desktop app is built on Electron, so it idles around 200 MB of RAM — Reddit's r/webdev threads and Hacker News comments mention this regularly. Real-time team collaboration only landed in the paid Cloud (it is not in the free desktop app), which has frustrated some open-source purists. And while OpenAPI 3.0 import is solid, gRPC, GraphQL, and WebSockets are still not first-class citizens — the team has flagged them on the public roadmap but they are not shipping yet. Vendors of testimonials on the homepage include developers from Ubuntu ("snap install mockoon"), and engineers at Localazy and Impala have published case studies on using it for production API design work.

Mockoon Pricing

Mockoon is a freemium product: the desktop app, CLI, and serverless package are 100% free and MIT-licensed. Mockoon Cloud is a paid layer on top for teams that need synchronization, real-time collaboration, hosted deployments, and AI generation.

Plan	Price (annual billing)	What's Included
Open Source (Desktop, CLI, Serverless)	$0 forever	Unlimited local mocks, all features, MIT licence, no account required
Solo (Cloud)	$10/month	1 deployed cloud mock, 10,000 monthly calls, 100 AI endpoints/month, web UI, sync across devices, 5 req/sec
Team (Cloud)	$100/month	5 seats, 3 deployed cloud mocks, 100,000 monthly calls, 200 AI endpoints per user, real-time collaboration, RBAC, audit trail, next-business-day support, 10 req/sec
Enterprise	Contact sales	Custom quotas, optional dedicated instances, choice of any Google Cloud region, single-tenant hosting, contractual 99.9% SLA, PO/invoicing

Cloud plans get a 14-day free trial with no credit card for users with a valid work email, and the company offers free licenses for eligible open-source projects and discounts for educational institutions.

Who Should Use Mockoon?

Best for: frontend, mobile, and full-stack developers who need a local mock API now; QA engineers running contract tests in CI; teams in regulated or air-gapped environments where a SaaS-only mock tool is a non-starter; and instructors who want a zero-friction way for students to practise consuming REST APIs.

Not ideal for: teams whose primary protocol is gRPC, GraphQL, or WebSockets (limited or no first-class support); organizations that require deeply integrated test-data management with their existing observability stack; and teams that want browser-only access without installing a desktop app — the Cloud web UI is in early access and gated behind a paid plan.

Pros and Cons

Pros:

• Zero account, zero internet, zero install friction — you can be productive in under 60 seconds, a claim repeated across hundreds of G2 and Product Hunt reviews
• True open source under MIT — fork it, ship it inside your enterprise, no rug pulls
• Powerful rules + Handlebars + Faker.js engine that rivals tools 5–10× the price
• OpenAPI 3.0 import/export is genuinely useful for API design workflows
• CLI + Docker image makes it a first-class citizen in CI pipelines

Cons:

• Electron-based desktop app uses ~200 MB RAM at idle — heavy for what it is
• Real-time collaboration is paid-only, which feels at odds with the open-source ethos
• No first-class gRPC, GraphQL, or WebSocket support yet
• Cloud regions are limited to US-Iowa and EU-Belgium on Solo and Team plans

Alternatives to Mockoon

The closest alternatives are Hoppscotch (free and open source, but more focused on API testing than mocking), Bruno (Git-friendly API client with mocking on the roadmap), Postman's Mock Servers (cloud-only and gated behind Postman's paid tiers), and WireMock (Java-based, much heavier but unbeatable for advanced contract testing). For sheer time-to-first-mock on a developer's laptop, Mockoon is the one we reach for first.

Verdict: Is Mockoon Worth It?

Yes, for almost everyone who builds against REST APIs. The free desktop app and CLI are best-in-class for their job, the company is independent and EU-based with privacy at the core, and the optional Cloud layer is honestly priced if you actually need team sync. Solo developers can stop reading and download it now. Small teams who already share a Git repo for their mock environments can stay on the open-source tier indefinitely. We dock points only for the Electron footprint and the still-missing gRPC/GraphQL story — otherwise this is a near-perfect tool. Final rating: 88/100.

Frequently Asked Questions

Is Mockoon free?

Yes. The Mockoon desktop app, CLI, and serverless package are 100% free and MIT-licensed forever, with no account required. Mockoon Cloud is an optional paid layer that starts at $10/month for the Solo plan.

What platforms does Mockoon support?

The desktop app runs on Windows, macOS, and Linux (including a Snap package on Ubuntu). The CLI runs anywhere Node.js or Docker runs. The Cloud web app is in early access on paid plans.

How does Mockoon compare to Postman Mock Servers?

Mockoon is open-source, runs entirely offline on your machine, and is free for unlimited local mocks. Postman's mocks are cloud-only and counted toward your paid quota. Mockoon also has more powerful response-rule matching, while Postman wins on sharing mocks via its workspace ecosystem.

Is Mockoon open source?

Yes — MIT-licensed and developed openly at github.com/mockoon/mockoon, with 8,200+ stars as of April 2026. Mockoon Cloud is a separate, source-available product layered on top.

Can Mockoon run in CI/CD pipelines?

Yes. The official mockoon/cli Docker image and Node CLI are built for headless use in GitHub Actions, GitLab CI, CircleCI, and any other runner. Many teams use it for contract testing against frozen mock environments.

Does Mockoon support OpenAPI?

Yes. Mockoon imports OpenAPI 3.0 and Swagger 2.0 specifications and exports the same — so you can round-trip a mock environment between Mockoon and your real API spec.