# Couper

> Couper is a lightweight open-source API gateway designed to support developers in building and running API-driven web projects.

Couper acts as an entry point for clients to your application (frontend API gateway) and an exit point to upstream services. It adds access control, observability, and backend connectivity on a separate architectural layer, keeping your core application code simple.

## Key Features

- **HTTP Request Routing / Forwarding**: Proxy component forwarding requests and responses between clients and upstream services. Create virtual endpoints and configure upstream URLs.
- **Web Serving**: Built-in file server and SPA (Single Page Application) asset serving.
- **Access Control**: JWT validation, OAuth2, OpenID Connect (OIDC), SAML, Basic Auth, and client/server certificate-based authentication.
- **API Aggregation**: Combine multiple upstream API calls into a single client-facing endpoint via request sequences.
- **Observability**: Structured logging, distributed tracing (OpenTelemetry), Prometheus metrics, and health checks.
- **Rate Limiting**: Configurable rate limiting for API protection.
- **WebSockets**: WebSocket proxy support.
- **TLS/mTLS**: Full TLS and mutual TLS support.
- **CORS**: Built-in Cross-Origin Resource Sharing configuration.
- **Error Handling**: Hierarchical error type system with configurable error handlers.

## Configuration

Couper uses HCL (HashiCorp Configuration Language) for its configuration files (`couper.hcl`). The syntax is easy to read, yet powerful and expressive. A VS Code extension is available for syntax highlighting and autocompletion.

## Installation

Available as:
- Container image on DockerHub: `coupergateway/couper`
- Binary from GitHub releases
- Homebrew: `brew tap coupergateway/couper && brew install couper`

## Links

- Website: https://couper.io
- Source code: https://github.com/coupergateway/couper
- Examples repository: https://github.com/coupergateway/couper-examples
- VS Code Extension: https://marketplace.visualstudio.com/items?itemName=couper.couperconf
- Docker Hub: https://hub.docker.com/r/coupergateway/couper

## Documentation

For detailed configuration reference, block definitions, access control setup, expressions, functions, error handling, and all other technical documentation:

- Full documentation: https://docs.couper.io
- Documentation for LLMs: https://docs.couper.io/llms.txt