A2A Client

Lets your agent discover and communicate with remote A2A (Agent-to-Agent) protocol agents. Two operations are available:

• discover — fetches the agent card from a remote A2A endpoint and returns its capabilities, name, description, and skills.
• send_message — sends a text message to a remote A2A agent and returns the response.

The tool is stateless: a fresh A2AAgent is created on every call using the per-endpoint configuration. Use make_a2a_client / makeA2AClient to control which endpoints the model may contact, with per-endpoint authentication, and to tune size limits.

Supported in: Python, TypeScript (Node.js, browsers).

Install required

Python

a2a_client requires the optional a2a extra:

pip install 'strands-agents[a2a]'

TypeScript

Requires the optional @a2a-js/sdk peer dependency:

npm install @a2a-js/sdk

Endpoint security

allowed_endpoints / allowedEndpoints is required and checked before any network connection is made, but it only gates the agent-card fetch. send_message is delivered to the url in that card, which may point to a different host, and HTTP redirects are not checked either. For full egress control, enforce it at the network layer.

Example:

TypeScript

import { Agent } from '@strands-agents/sdk'
import {
  ClientFactory,
  DefaultAgentCardResolver,
  JsonRpcTransportFactory,
  RestTransportFactory,
  createAuthenticatingFetchWithRetry,
} from '@a2a-js/sdk/client'
import { makeA2AClient } from '@strands-agents/sdk/vended-tools/a2a-client'

const authFetch = createAuthenticatingFetchWithRetry(fetch, {
  headers: async () => ({ Authorization: 'Bearer your-token' }),
  shouldRetryWithHeaders: async () => undefined,
})

const a2aClient = makeA2AClient({
  allowedEndpoints: [
    // No auth needed
    'https://agent.example.com',
    // Custom ClientFactory for authenticated requests
    [
      'https://researcher.example.com',
      new ClientFactory({
        transports: [
          new JsonRpcTransportFactory({ fetchImpl: authFetch }),
          new RestTransportFactory({ fetchImpl: authFetch }),
        ],
        cardResolver: new DefaultAgentCardResolver({ fetchImpl: authFetch }),
      }),
    ],
  ],
})

const agent = new Agent({ tools: [a2aClient] })
await agent.invoke('What has the research agent found recently?')

Python

import httpx
from a2a.client import ClientConfig
from strands import Agent
from strands.vended_tools import make_a2a_client

a2a_client = make_a2a_client(
    allowed_endpoints=[
        "https://agent.example.com",
        ("https://researcher.example.com", ClientConfig(
            httpx_client=httpx.AsyncClient(
                headers={"Authorization": "Bearer your-token"},
                timeout=60.0,
            ),
        )),
    ],
)
agent = Agent(tools=[a2a_client])
agent("What has the research agent found recently?")

Full API reference: TypeScript

Tags

tool-authoring26