Crate mcp_proxy 

MCP Proxy – config-driven reverse proxy with auth, rate limiting, and observability.

This crate can be used as a library to embed an MCP proxy in your application, or run standalone via the mcp-proxy CLI.

Library Usage

Build a proxy from a TOML config file:

use mcp_proxy::{Proxy, ProxyConfig};

let config = ProxyConfig::load("proxy.toml".as_ref())?;
let proxy = Proxy::from_config(config).await?;

// Embed in an existing axum app
let (router, session_handle) = proxy.into_router();

// Or serve standalone
// proxy.serve().await?;

Or build programmatically with ProxyBuilder:

use mcp_proxy::ProxyBuilder;

let proxy = ProxyBuilder::new("my-proxy")
    .listen("0.0.0.0", 9090)
    .http_backend("api", "http://api:8080")
    .stdio_backend("files", "npx", &["-y", "@mcp/server-files"])
    .build()
    .await?;

proxy.serve().await?;

Hot Reload

Enable hot_reload = true in the config to watch the config file for new backends. The proxy will add them dynamically without restart.

Re-exports

pub use builder::ProxyBuilder;

pub use config::ProxyConfig;

Modules

access_log

Structured access logging middleware.

admin

Admin API for proxy introspection.

admin_tools

MCP admin tools for proxy introspection.

alias

Tool aliasing middleware for the proxy.

bearer_scope

Per-token tool scoping for bearer token authentication.

builder

Programmatic proxy builder for library users.

cache

Response caching middleware for the proxy.

canary

Canary / weighted routing middleware.

coalesce

Request coalescing middleware for the proxy.

composite

Composite tool middleware for fan-out to multiple backend tools.

config

Proxy configuration types and TOML parsing.

discovery

BM25-based tool discovery and search.

failover

Backend failover middleware.

filter

Capability filtering middleware for the proxy.

inject

Argument injection middleware for tool calls.

introspection

OAuth 2.1 token introspection and authorization server discovery.

mcp_json

Support for .mcp.json / mcp.json config format.

metrics

Prometheus metrics middleware for the proxy.

mirror

Traffic mirroring / shadowing middleware.

outlier

Passive health checks via outlier detection.

param_override

Parameter override middleware for tool customization.

rbac

Role-based access control middleware for the proxy.

reload

Hot reload: watch the config file for changes and manage backends dynamically.

retry

Retry middleware for per-backend request retries with exponential backoff.

token

Token passthrough middleware for forwarding client credentials to backends.

validation

Request validation middleware for the proxy.

ws_transport

WebSocket client transport for connecting to WebSocket-based MCP backends.

Structs

Proxy

A fully constructed MCP proxy ready to serve or embed.