MCP Stdio Bridge

A generic, professional-grade gateway that bridges Model Context Protocol (MCP) servers between SSE (Server-Sent Events) and Stdio transports.

Features

• Generic Bridge: Works with any executable that speaks MCP over stdio.

• Command Wrapper Mode: Directly wrap any CLI utility (like wp-cli, git, or custom scripts) into a restricted MCP server without writing external scripts.

• Dual Transport Support: Run over SSE (HTTP/HTTPS) for remote access or Stdio for local use by MCP clients.

• 100% Test Coverage: Exhaustive test suite ensuring stability across all transports, operational modes, and failure paths.

• YAML Configuration: Easily manage settings via a central config file.

• Dynamic Configuration Reload: Opt-in feature to live-reload settings from config.yaml without dropping active sessions.

• Idle Session Timeouts: Automatically terminates stalled proxy and wrapper sessions to prevent resource leaks.

• Process Management: Automatically spawns, manages, and cleans up subprocesses for bridging.

• Security:

  • API key authentication (Header or Query Param).
  • Restricted argument prefixing and regex filtering for wrapped commands.
  • Built-in Directory Traversal Protection for local tool execution.
  • Environment Scrubbing: Allowlist/Denylist variables passed to subprocesses.
  • Secret Masking: Sensitive keys are automatically hidden from logs.
  • Connection limiting and message size throttling.
  • SSL/TLS with client certificate and CRL support.
  • HSTS and secure security headers.

Installation

Install the package using pip:

pip install mcp-stdio-bridge

Documentation

For detailed information on configuring and deploying the bridge, see:

• docs/configuration.md: Full settings reference and JSON Schema.
• docs/deployment.md: Docker and local execution guides.
• docs/mcp-servers.md: Integration requirements for MCP servers.
• docs/roadmap.md: Future considerations and planned features.

Architecture & Design

To understand the internal logic and security model, refer to:

• docs/architecture.md: Modular structure and transport/mode design.
• docs/security.md: Detailed security features and sandboxing.
• docs/workflows.md: Sequential operational flows.

Examples

Check the examples/ directory for templates covering common use cases:

• wp-cli-wrapper.yaml: Manage WordPress via MCP (Mix of Allowlist/Denylist).
• git-wrapper.yaml: Expose Git operations to local clients (Allowlist-only).
• sqlite-proxy.yaml: Bridge an existing SQLite MCP server to SSE.
• security-patterns.yaml: Advanced regex-based security filtering.
• docker-tool-wrapper.yaml: Using custom environment variables per tool.

Example config.yaml:

host: "127.0.0.1"
port: 8000
command: "python your_mcp_server.py"
verbose: true
api_key: "your-secret-key"
max_connections: 5
cors_origins: ["*"]
# ssl_keyfile: "path/to/key.pem"
# ssl_certfile: "path/to/cert.pem"

Running the Bridge

mcp-stdio-bridge

Docker

You can run the bridge using Docker:

# Build the image
docker build -t mcp-stdio-bridge .

# Run with a mounted config file
docker run -p 8000:8000 -v $(pwd)/config.yaml:/app/config.yaml mcp-stdio-bridge

Alternatively, use Docker Compose:

docker-compose up -d

Customization Arguments

Argument	Description	Default
--host	Host to bind the server to	0.0.0.0
--port	Port to bind the server to	8000
--command	The command to run for each session (Proxy Mode)	None
--mode	Operation mode (proxy or command-wrapper)	proxy
--transport	Transport protocol (sse or stdio)	sse
--api-key	Optional API key for authentication	None
--max-connections	Max concurrent subprocesses	10
--max-message-size	Max message size in bytes	1048576
--ssl-keyfile	Path to SSL key file	None
--ssl-certfile	Path to SSL cert file	None
--ssl-keyfile-password	Password for SSL key file	None
--ssl-ca-certs	Path to SSL CA certificates file	None
--ssl-crlfile	Path to SSL CRL file	None
--ssl-client-cert-required	Require client certificates	False
--ssl-protocol	SSL protocol (TLSv1_2, TLSv1_3)	TLSv1_2
--ssl-ciphers	SSL ciphers	None
--hsts	Enable HSTS	False
--no-security-headers	Disable default security headers	False
--cors-origins	CORS origins (space-separated)	["*"]
--idle-timeout	Idle timeout for proxy sessions (seconds)	3600
--env-allowlist	Allowlist of environment variables	None
--env-denylist	Denylist of environment variables	[...]
--log-level	Set the logging level (DEBUG, INFO, etc.)	INFO
--logging-config	Path to a custom logging config file	None
--watch-config	Enable dynamic config reloading	False
-v, --verbose	Enable verbose logging	False

Development

Install all dependencies (including test and dev extras):

pip install -e ".[dev,test]"

Run the full test suite (the --timeout=10 flag is required — SSE transport tests can hang without it):

pytest --timeout=10

Lint, type-check, and security scan:

ruff check src tests
mypy src
bandit -r src -c pyproject.toml

License

This is free and unencumbered software released into the public domain. For more information, please refer to the LICENSE file or http://unlicense.org/.