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Lightweight, blazing fast, cross-platform OpenAPI 3 mock server with validation


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API Sprout

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A simple, quick, cross-platform API mock server that returns examples specified in an API description document. Features include:

  • OpenAPI 3.x support
    • Uses operation examples or generates examples from schema
  • Load from a URL or local file (auto reload with --watch)
  • CORS headers enabled by default
  • Accept header content negotiation
    • Example: Accept: application/*
  • Prefer header to select response to test specific cases
    • Example: Prefer: status=409
  • Server validation (enabled with --validate-server)
    • Validates scheme, hostname/port, and base path
    • Supports localhost out of the box
    • Use the --add-server flag, in conjunction with --validate-server, to dynamically include more servers in the validation logic
  • Request parameter & body validation (enabled with --validate-request)
  • Configuration via:
    • Files (/etc/apisprout/config.json|yaml)
    • Environment (prefixed with SPROUT_, e.g. SPROUT_VALIDATE_SERVER)
    • Commandline flags

Usage is simple:

# Load from a local file
apisprout my-api.yaml

# Validate server name and use base path
apisprout --validate-server my-api.yaml

# Dynamically Include a new server / path in the validation
apisprout --add-server http://localhost:8080/mock --validate-server my-api.yaml

# Load from a URL

Docker Image

A hosted API Sprout Docker image is provided that makes it easy to deploy mock servers or run locally. For example:

docker pull danielgtaylor/apisprout
docker run -p 8000:8000 danielgtaylor/apisprout

Configuration can be passed via environment variables, e.g. setting SPROUT_VALIDATE_REQUEST=1, or by passing commandline flags. It is also possible to use a local API description file via Docker Volumes:

# Remember to put the full path to local archive YAML in -v
docker run -p 8000:8000 -v $FULLPATH/localfile.yaml:/api.yaml danielgtaylor/apisprout /api.yaml


Download the appropriate binary from the releases page.

Alternatively, you can use go get:

go get

Extra Features

Remote Reload

If your API spec is loaded from a remote URL, you can live-reload it by hitting the /__reload endpoint.

Health Check

A simple endpoint which returns status code 200 is available at /__health. This endpoint successfully returns 200 even if --validate-server is turned on, and the endpoint is being accessed from a non-validated host.


Contributions are very welcome. Please open a tracking issue or pull request and we can work to get things merged in.

Release Process

The following describes the steps to make a new release of API Sprout.

  1. Merge open PRs you want to release.
  2. Select a new semver version number (major/minor/patch depending on changes).
  3. Update to describe changes.
  4. Create a commit for the release.
  5. Tag the commit with git tag -a -m 'Tagging x.y.z release' vx.y.z.
  6. Build release binaries with ./
  7. Push the commit and tags.
  8. Upload the release binaries.


Copyright © 2018-2019 Daniel G. Taylor