The Open-Source Mock API Tool Across Protocols

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About

Mokapi is an open-source, local-first mock API tool to develop and test faster. Simulate complete environments driven by OpenAPI and AsyncAPI specifications without external dependencies.

It supports HTTP/REST, Apache Kafka, MQTT, Websocket, LDAP, and SMTP from a single tool, making it useful across the whole stack, not just for REST APIs.

Use it to:

• Build frontend UIs before the backend exists
• Test error states, timeouts, and edge cases safely
• Run reliable CI/CD pipelines without external dependencies
• Validate API contracts before writing implementation code

Quick Start

Try the mock API instantly:

npx go-mokapi https://petstore3.swagger.io/api/v3/openapi.json

curl http://localhost/api/v3/pet/1 -H 'Accept: application/json'

A working mock from a public OpenAPI spec in under a minute. No installation required.

Feature

Feature	Description
Multi-protocol	HTTP/HTTPS, Apache Kafka, MQTT, Websocket, LDAP, SMTP
Spec-driven	Uses OpenAPI and AsyncAPI as the source of truth
JavaScript scripting	Customize responses, simulate errors, add delays
Everything as code	Version-controlled, CI/CD-ready, no UI required
Config patching	Override parts of a spec without modifying the original
Built-in dashboard	Real-time request and response viewer at localhost:8080
Flexible providers	Load specs from files, URLs, Git repos, or NPM packages

Usage

Basic HTTP mock

npx go-mokapi ./openapi.yaml

With a remote spec

npx go-mokapi https://example.com/api/openapi.json

Docker

docker run -it -p 8080:8080 -p 80:80 \
  -v $(pwd):/data mokapi/mokapi /data/openapi.yaml

Dashboard

Open http://localhost:8080 to view live requests, responses, and logs.

Configuration

JavaScript scripting

import { on } from 'mokapi'

export default function() {
  on('http', (request, response) => {
    // Return 404 for specific IDs
    if (request.path.petId === '999') {
      response.statusCode = 404
      return
    }

    // Customize response data
    response.data.name = 'Custom Pet Name'
  })
}

Spec patching

Override parts of your OpenAPI spec for specific test scenarios without touching the original file. See the configuration guide for details.

Tutorials

Explore tutorials that walk you through mocking different protocols and scenarios:

• Get started with REST API Mocking
  Deploy a REST mock API using OpenAPI specification

• Mock Kafka with AsyncAPI
  Simulate Kafka topics and validate message producers

• Mock LDAP Authentication
  Test authentication flows without a real LDAP server

• Mock SMTP Mail Servers
  Test email workflows without sending real messages

• CI/CD Integration with GitHub Actions
  Run Mokapi in automated test pipelines

More at mokapi.io/resources

Documentation

• Getting Started Guide
• HTTP/REST API Documentation
• Kafka Documentation
• LDAP Documentation
• SMTP/Mail Documentation
• JavaScript API Reference
• Configuration Guide

Support the Project

If Mokapi saves you time, consider buying me a coffee. It helps keep the project going.

Merch

License

MIT License - see LICENSE for details.

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