What is Handler?

Handler is an open-source A2A protocol client for software engineers building, testing, and operating agentic systems. It gives you a terminal-native control surface for A2A services: an interactive TUI for exploration, a scriptable CLI with structured output for automation, and an MCP server so other agents can call A2A services through Handler. Use Handler when you need to:

inspect and validate agent cards before debugging deeper protocol issues
send messages, stream events, and manage tasks from shell scripts or CI
configure global or repo-scoped A2A servers with bearer, API key, mTLS, or OAuth2 client credentials auth
expose A2A operations as MCP tools for agent harnesses such as Amp or Pi

Install

Install Handler from the PyPI package as a uv tool:

uv tool install a2a-handler

Or with pipx:

pipx install a2a-handler

Or with pip:

pip install a2a-handler

First commands

Open the interactive terminal UI:

handler tui

Inspect an A2A server’s agent card:

handler card get --url http://localhost:8000

Send a message from the CLI:

handler message send --url http://localhost:8000 --text "hello"

Open the full documentation:

handler docs

If you want another agent to use Handler through MCP, add handler mcp to that agent’s MCP server configuration. See MCP server.

Choose your path

Quickstart walks through install, first message, and configured servers.
TUI and web UI covers the interactive workflow.
Messages, tasks, and sessions explains CLI automation and structured output.
Configured servers and authentication cover production connection configuration.
MCP server shows how to let MCP clients call A2A agents through Handler.
CLI reference lists commands, flags, and machine-readable schema helpers.

Getting started

Overview

What is Handler?

Install

First commands

Choose your path

​What is Handler?

​Install

​First commands

​Choose your path

What is Handler?

Install

First commands

Choose your path