Agent Gateway (A2A Protocol) - Overview

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Agent Gateway (A2A Protocol) - Overview

Add A2A Agents on LiteLLM AI Gateway, Invoke agents in A2A Protocol, track request/response logs in LiteLLM Logs. Manage which Teams, Keys can access which Agents onboarded.

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:::tip

LiteLLM follows the A2A (Agent-to-Agent) Protocol for invoking agents.

:::

Adding your Agent

Add A2A Agents

You can add A2A-compatible agents through the LiteLLM Admin UI.

1. Navigate to the Agents tab
2. Click Add Agent
3. Enter the agent name (e.g., ij-local) and the URL of your A2A agent

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The URL should be the invocation URL for your A2A agent (e.g., http://localhost:10001).

Add Azure AI Foundry Agents

Follow this guide, to add your azure ai foundry agent to LiteLLM Agent Gateway

Add Vertex AI Agent Engine

Follow this guide, to add your Vertex AI Agent Engine to LiteLLM Agent Gateway

Add Bedrock AgentCore Agents

Follow this guide, to add your bedrock agentcore agent to LiteLLM Agent Gateway

Add LangGraph Agents

Follow this guide, to add your langgraph agent to LiteLLM Agent Gateway

Add Pydantic AI Agents

Follow this guide, to add your pydantic ai agent to LiteLLM Agent Gateway

Invoking your Agents

See the Invoking A2A Agents guide to learn how to call your agents using:

• A2A SDK - Native A2A protocol with full support for tasks and artifacts
• OpenAI SDK - Familiar /chat/completions interface with a2a/ model prefix

Tracking Agent Logs

After invoking an agent, you can view the request logs in the LiteLLM Logs tab.

The logs show:

• Request/Response content sent to and received from the agent
• User, Key, Team information for tracking who made the request
• Latency and cost metrics

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Forwarding LiteLLM Context Headers

When LiteLLM invokes your A2A agent, it sends special headers that enable:

• Trace Grouping: All LLM calls from the same agent execution appear under one trace
• Agent Spend Tracking: Costs are attributed to the specific agent

To enable these features, your A2A server must forward these headers to any LLM calls it makes back to LiteLLM.

Implementation Steps

Step 1: Extract headers from incoming A2A request

    """Extract X-LiteLLM-* headers from incoming A2A request."""
    all_headers = request.call_context.state.get('headers', {})
    return {
        k: v for k, v in all_headers.items() 
        if k.lower().startswith('x-litellm-')
    }

Step 2: Forward headers to your LLM calls Pass the extracted headers when making calls back to LiteLLM:

headers = get_litellm_headers(request)

client = OpenAI(
    api_key="sk-your-litellm-key",
    base_url="http://localhost:4000",
    default_headers=headers,  # Forward headers
)

response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Hello"}]
)

from langchain_openai import ChatOpenAI

headers = get_litellm_headers(request)

llm = ChatOpenAI(
    model="gpt-4o",
    openai_api_key="sk-your-litellm-key",
    base_url="http://localhost:4000",
    default_headers=headers,  # Forward headers
)

import litellm

headers = get_litellm_headers(request)

response = litellm.completion(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Hello"}],
    api_base="http://localhost:4000",
    extra_headers=headers,  # Forward headers
)

import httpx

headers = get_litellm_headers(request)
headers["Authorization"] = "Bearer sk-your-litellm-key"

response = httpx.post(
    "http://localhost:4000/v1/chat/completions",
    headers=headers,
    json={"model": "gpt-4o", "messages": [{"role": "user", "content": "Hello"}]}
)

Result

With header forwarding enabled, you'll see:

Trace Grouping in Langfuse:

<Image img={require('../img/a2a_trace_grouping.png')} style={{width: '80%', display: 'block', margin: '0', borderRadius: '8px'}} />

Agent Spend Attribution:

<Image img={require('../img/a2a_agent_spend.png')} style={{width: '80%', display: 'block', margin: '0', borderRadius: '8px'}} />

API Reference

Endpoint

POST /a2a/{agent_name}/message/send

Authentication

Include your LiteLLM Virtual Key in the Authorization header:

Authorization: Bearer sk-your-litellm-key

Request Format

LiteLLM follows the A2A JSON-RPC 2.0 specification:

{
  "jsonrpc": "2.0",
  "id": "unique-request-id",
  "method": "message/send",
  "params": {
    "message": {
      "role": "user",
      "parts": [{"kind": "text", "text": "Your message here"}],
      "messageId": "unique-message-id"
    }
  }
}

Response Format

{
  "jsonrpc": "2.0",
  "id": "unique-request-id",
  "result": {
    "kind": "task",
    "id": "task-id",
    "contextId": "context-id",
    "status": {"state": "completed", "timestamp": "2025-01-01T00:00:00Z"},
    "artifacts": [
      {
        "artifactId": "artifact-id",
        "name": "response",
        "parts": [{"kind": "text", "text": "Agent response here"}]
      }
    ]
  }
}

Agent Registry

Want to create a central registry so your team can discover what agents are available within your company?

Use the AI Hub to make agents public and discoverable across your organization. This allows developers to browse available agents without needing to rebuild them.