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OpenAPI Mock

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What OpenAPI Mock is

OpenAPI Mock is a free, open-source server for generating mock API responses from OpenAPI schemas or examples. It supports OpenAPI 3.x specifications in JSON and YAML, loaded from a local file or a URL. Response settings can ignore examples, use them when present, or use them exclusively. The server supports HTTP and content negotiation through the Accept header. It returns JSON, while XML generation is basic and does not include XML tags. OpenAPI Mock can run as a standalone application on Linux or Windows, or in Docker; Docker Compose usage is also documented. Settings can come from command-line options, environment variables, or YAML and JSON configuration files. A validate command can check whether a specification can be handled, including in Continuous Integration, but reports critical errors without details. Local references work, while remote and URL references do not. Request-data validation and forcing a custom response schema are unsupported. Combined schema types work except for the not tag and discriminator. The project is licensed under MIT.

Who it suits

It suits developers who need mock HTTP responses based on OpenAPI specifications and can deploy a standalone server or use Docker. Its configuration and validation options may also fit teams incorporating specification checks into CI.

What it does well

  • Free and open source under the MIT License
  • Supports OpenAPI 3.x in JSON and YAML
  • Responses can use schemas or examples
  • Runs on Linux, Windows, or Docker
  • Configuration supports CLI, environment variables, YAML, and JSON

What to know first

  • XML output is basic and omits XML tags
  • Remote and URL references are unsupported
  • Request-data validation is unsupported
  • Validation errors lack details

Limits

Remote and URL references, request-data validation, and forcing a custom response schema are unsupported. XML generation is basic, and the validate command reports critical errors without details.

Getting started

  1. Visit the project at https://github.com/muonsoft/openapi-mock.
  2. Provide an OpenAPI 3.x specification in JSON or YAML from a local file or URL.
  3. Choose a standalone Linux or Windows deployment, or use Docker or Docker Compose.
  4. Configure the server with command-line options, environment variables, or YAML or JSON files.
  5. Select whether responses should ignore examples, use them when present, or use them exclusively.
  6. Run the validate command if you want to check whether the application can handle the specification.

Verdict

OpenAPI Mock offers flexible response generation and deployment options for OpenAPI 3.x. Its reference and request-validation limits, along with sparse validation errors, matter if those capabilities are needed.

Questions

Does OpenAPI Mock cost anything?

It is free and open source under the MIT License.

Which OpenAPI formats does it support?

It supports OpenAPI 3.x specifications in JSON and YAML, loaded from a local file or a URL.

Where can I run it?

It can run as a standalone application on Linux or Windows, in a Docker container, or with Docker Compose.

Does it validate API requests?

No. Validating request data is listed as unsupported.

Can it resolve remote references?

No. Local references are supported, but remote and URL references are not.

What response formats does it support?

JSON responses are supported. XML response generation has basic support and does not include XML tags.

Facts from OpenAPI Mock's own pages

CI use
The usage guide says its specification validation command can be useful for Continuous Integration, but reports only critical errors without details. · github.com, 3 Oct 2026
Configuration
The server can be configured through command-line options, environment variables, or YAML and JSON configuration files. · github.com, 3 Oct 2026
Container integration
The project documents use with Docker and Docker Compose. · github.com, 3 Oct 2026
Content negotiation
The server supports content negotiation using the Accept header. · github.com, 2 Oct 2026
Deployment
The README says it can run as a standalone application on Linux or Windows, or in a Docker container. · github.com, 3 Oct 2026
License
The repository states that the project is licensed under the MIT License. · github.com, 3 Oct 2026
Maker identity
The repository is published under the GitHub account muonsoft; the repository page does not state a headquarters or founding date. · github.com, 2 Oct 2026
OpenAPI support
The project supports OpenAPI 3.x specifications. · github.com, 3 Oct 2026
Purpose
OpenAPI Mock is an API mock server that generates random response data from specified schemas. · github.com, 3 Oct 2026
Reference limits
Remote and URL reference resolving, request-data validation, and forcing a custom response schema are listed as unsupported. · github.com, 2 Oct 2026
Reference support
Local references are supported, but remote and URL references are not supported. · github.com, 3 Oct 2026
Request validation
Validating request data is listed as unsupported. · github.com, 3 Oct 2026
Response formats
JSON response generation is supported, while XML generation has basic support without XML tags. · github.com, 3 Oct 2026
Response generation
Mock responses can be generated from schemas or examples, with content negotiation based on the Accept header. · github.com, 3 Oct 2026
Schema limits
Combined types are supported except for the not tag and discriminator, and the application detects response schemas automatically rather than accepting a forced custom response schema. · github.com, 3 Oct 2026
Specification input
It can load a specification from a local file or URL, in JSON or YAML format. · github.com, 3 Oct 2026
Validation limit
The validate command reports only critical errors without details, and the documentation recommends another tool for a better specification-validation experience. · github.com, 2 Oct 2026

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