A fast, zero-dependency CLI tool for developers to mock, stub, and proxy HTTP and gRPC APIs — written in Go.
No external dependencies on your app. Just point your frontend or service at apitwin instead of the real API.
Switch between response scenarios by editing a config file — changes apply instantly with no restart.
Mock only the endpoints you're actively building. Forward everything else to the real backend.
CRUD operations with one JSON file per resource. Perfect for realistic data management during development.
Full support for both HTTP/REST APIs and gRPC services with automatic proto generation.
Reference data from other stub files with filtering and transformation using the {{ref:...}} syntax.
Iterate over collections and reshape each item with $each / $template syntax for building complex interconnected responses.
Time-based state progression across response cases for testing different application states.
Dynamic content generation with {{uuid}}, {{now}}, {{timestamp}} and other template tokens.
Generate complete mock APIs from OpenAPI 3 specifications with high-quality stub synthesis.
Browser dashboard at /__ui/ for inspecting routes, testing requests, and watching config changes in real time.
Proxy a real API, save responses automatically, then replay them offline for consistent testing.
