Mock APIs Without the Setup Headache

You need to test a client against an API that doesn't exist yet, or you want to inspect what a webhook is actually sending you. Spinning up a real backend just to see request payloads is overkill. Insomnia Mockbin, maintained by Kong, is a tool built for exactly this kind of work.

What It Does

Insomnia Mockbin is a mock server that lets you create endpoints and inspect the requests hitting them. It uses the HAR (HTTP Archive) format for storing request and response data, which means the data it captures follows a well-established spec rather than some proprietary structure.

The server supports multiple output formats: JSON, YAML, XML, and HTML. It handles proxy scenarios properly by reading the X-Forwarded-* headers to resolve client IPs, so it behaves correctly when it's sitting behind a reverse proxy. It also supports HTTP method override, either through the X-HTTP-Method-Override header or a _method query string parameter. You can create custom bins for experimenting with log collection.

It's a Node.js application backed by Redis. Redis is technically optional for starting the server, but you won't be able to set or retrieve response bins without it. The project is source-visible but not open-source, so you'll want to check the LICENSE before using it.

Why It's Cool

• HAR format is a smart foundation. By using the HTTP Archive format, the captured data is portable and inspectable with existing HAR tooling. You're not locked into a custom data format that only this tool understands.

• Proxy awareness is baked in. A lot of mock servers fall apart when you put them behind a load balancer or reverse proxy because they report the proxy's IP instead of the client's. Mockbin reads the X-Forwarded-* headers, so IP resolution works as you'd expect.

• Method override support is practical. If you're stuck with a client that can only send GET or POST (older HTTP clients, some webhook providers, certain embedded systems), the X-HTTP-Method-Override header and _method query parameter let you route those requests as if they were PUT, DELETE, or anything else.

• Custom bins for log collection. Beyond just mocking responses, you can create bins specifically for collecting and experimenting with logs. This is useful when you're debugging integration flows and need to see exactly what's coming through.

• Kong maintains it. The same team behind the Kong API Gateway and the Insomnia API client maintains this. That's relevant if you're already in that ecosystem, and it suggests the project won't be abandoned next week.

• Docker and local dev paths both exist. You can run it with docker compose up if you just want to try it, or clone it locally if you're contributing or need to modify it.

• Supply chain transparency. The project produces SBOMs for both container images and the source repository. Container images are signed with cosign, and there are documented steps for verifying signatures and provenance. Separate images exist for cloud-hosted and self-hosted mocks. If you work in an environment where you need to verify what you're deploying, this matters.

How to Try It

The fastest path is Docker:

docker compose up

If you want to run it locally, you'll need Redis first:

brew install redis
brew services start redis

Then clone and start:

git clone https://github.com/Kong/mockbin.git ./mockbin
cd mockbin
cp .env.sample .env
brew install fnm
fnm use
npm install
npm start

For development with auto-reload, use npm run dev. For debug logs, prefix with DEBUG=mockbin.

The full API documentation lives in the docs directory. Deployment options are covered at developer.konghq.com. The repository is at github.com/Kong/insomnia-mockbin.

Final Thoughts

Insomnia Mockbin is a focused tool that does one thing well: capture and mock HTTP traffic without requiring you to build anything. It's not trying to be a full API lifecycle platform. It's a mock server with sensible defaults, proper proxy handling, and a format that won't trap your data. If you're already using Kong or Insomnia, it fits naturally into that workflow. If you're not, it's still worth a look the next time you need to stand up a quick endpoint and see what's hitting it.

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