Handler is an open-source A2A Protocol client and developer toolkit.

It provides a CLI and TUI for communicating with remote agents, an MCP server for bridging AI assistants into the A2A ecosystem, a reference server agent implementation, push notification support, and agent card validation. Whether you're building agents, integrating with existing ones, or exploring agent-to-agent communication, Handler gives you the observability and control you need from your terminal.

Handler is for developers, researchers, and teams working with AI agents. If you're building agents that speak A2A, Handler helps you test and debug them. If you're integrating with existing A2A agents, Handler gives you a fast way to explore their capabilities. If you want your AI assistant to communicate with other agents, Handler's MCP server bridges that gap. And if you're just curious about agent-to-agent communication, Handler is a great place to start.

Install with uv:

uv tool install a2a-handler

Or with pipx:

pipx install a2a-handler

Or with pip:

pip install a2a-handler

Or, run from an ephemeral environment:

# With uv
uvx --from a2a-handler handler

# With pipx
pipx run a2a-handler

A hermetically sealed development environment is available with Nix:

nix develop

This provides Python, uv, and just with all commands ready to use.

For usage documentation, see the Handler docs.

See CONTRIBUTING.md.