OpenAPI Server
OpenAPI Server is a local mock server for API development and end-to-end testing.
What OpenAPI Server is
OpenAPI Server is a local mock server for API development and end-to-end testing. It helps teams build a single-page application before a backend is ready by returning predictable mock responses, while also allowing selected requests to proxy to a real server. The project validates OpenAPI 3 and Swagger/OpenAPI 2 YAML files, supports multiple specifications or directories, and checks for path and method conflicts. Mocks can be JSON files, JavaScript modules, or Express middleware. Matching mocks are enabled by default and take precedence over proxying; response validation can be enabled when proxying. Additional capabilities include static file serving, HTTP and HTTPS, watch mode, and configuration through CLI options, environment variables, or files. It can run as an Express application or router and accepts custom middleware. Installation uses npm from GitHub, and the quick start serves localhost:3000/api. Node.js 18 or later is required.
Good
- Validates OpenAPI 3 and Swagger/OpenAPI 2 specifications
- Supports JSON, JavaScript, and Express middleware mocks
- Can proxy unmatched requests to a backend
- Includes HTTP, HTTPS, static files, and watch mode
- ISC-licensed open-source package
Watch out
- Requires Node.js 18 or later
- TypeScript mock files are not allowed at runtime
- API access requires local installation from GitHub
Who it suits
It suits developers prototyping APIs, building single-page applications before backend services exist, or running end-to-end tests with controlled responses. Teams needing local or self-hosted operation can use its Express integration and configuration options.
Verdict
OpenAPI Server provides a configurable local layer for mocking, proxying, and validating API behavior. Its multiple mock formats and Express integration make it useful when frontend work or predictable tests must proceed before a backend is complete.
The facts
Each one read from OpenAPI Server's own pages, with the date it was checked.
What it does
- Additional features
- It supports serving static files, HTTP and HTTPS, watch mode, and custom Express middleware.checked 5 Oct 2026
- Configuration
- Configuration is available through command-line options, environment variables, and environment files.checked 5 Oct 2026
- Default behavior
- Mocks are enabled by default and take precedence over proxying when a matching mock exists.checked 4 Oct 2026
- End-to-end testing
- Mocks can provide predictable API responses for end-to-end tests.checked 4 Oct 2026
- Install
- The README instructs users to install it from its GitHub repository with npm.checked 4 Oct 2026
- Installation
- The README gives a GitHub-based npm install command and a quick start that serves the API at localhost:3000/api.checked 5 Oct 2026
- Integration
- The project can run as a command-line server or be imported programmatically as an application or Express router.checked 5 Oct 2026
- Intended use
- The README describes using it to mock services while prototyping a single-page application without a working backend.checked 4 Oct 2026
- License
- The package declares the ISC license.checked 5 Oct 2026
- Mock formats
- Mocks can be JSON files, JavaScript modules, or Express middleware.checked 4 Oct 2026
- Mocking
- Mocks can be JSON files, JavaScript modules, or Express middleware, and mocks are enabled by default.checked 5 Oct 2026
- Multiple specifications
- It supports multiple specification files and directories and checks paths and methods for conflicts.checked 4 Oct 2026
- Notable limits
- JavaScript mocks must run at runtime; the README says TypeScript mock files are not allowed because they cannot be transpiled at runtime.checked 4 Oct 2026
- OpenAPI support
- It validates OpenAPI version 3 and Swagger version 2 specifications in YAML format.checked 5 Oct 2026
- Other features
- The README lists a static file server, HTTP and HTTPS support, watch mode, and configuration through environment variables, files, or CLI parameters.checked 4 Oct 2026
- Proxy
- When proxying is enabled, valid requests without a matching mock are forwarded to the configured backend.checked 5 Oct 2026
- Proxy and validation
- It can proxy requests to another server and optionally validate responses.checked 4 Oct 2026
- Publishing security
- The README says releases use npm Trusted Publishing with GitHub Actions OIDC and provenance.checked 5 Oct 2026
- Purpose
- OpenAPI Server is a local mock server for development that can proxy requests to a real backend.checked 5 Oct 2026
- Response validation
- The server can optionally validate responses.checked 5 Oct 2026
- Runtime requirement
- The package declares Node.js version 18 or later as its engine requirement.checked 5 Oct 2026
- Use case
- The README describes using it to develop a single-page application before its backend is ready and to run end-to-end tests with predictable API responses.checked 5 Oct 2026
The company
- Maker location
- The Intesys GitHub organization profile lists Italy as its location.checked 4 Oct 2026
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