Adk Composio Tool Router

Composio Tool Router for ADK agents

Composio is a hosted MCP server that exposes ~1000 third-party toolkits — Gmail, GitHub, Slack, Notion, Linear, Calendar, Stripe, HubSpot, every major SaaS — behind a single MCP endpoint. Composio handles auth (OAuth flows, token refresh, per-user credentials), tool discovery (the agent sees only the toolkits you've connected), and execution. You wire it up once; your agent gains broad integration coverage without authoring per-service tools.

nuvel new <name> --with-composio ships with this already wired. This skill explains what that flag actually does and how to operate it.

What --with-composio ships

The overlay drops one file into your agent: <package>/tools/composio_mcp.py, exporting build_composio_mcp_toolset(). The agent's tools/__init__.py calls it at startup; if COMPOSIO_API_KEY is set, the agent gains a McpToolset wrapping Composio's hosted MCP server.

# Roughly what runs at agent startup
composio = Composio()
session = composio.create(user_id=os.getenv("COMPOSIO_USER_ID", "default"))
return McpToolset(
    connection_params=StreamableHTTPConnectionParams(
        url=session.mcp.url,
        headers=session.mcp.headers,
    ),
)

If COMPOSIO_API_KEY is unset, the toolset gracefully no-ops and the agent starts with only its local tools. The flag is safe to ship; deployments without the key just don't get the integrations.

The two env vars

In single-tenant agents you can leave COMPOSIO_USER_ID unset and everything works. In multi-tenant agents you'll want to thread the real user ID into this — see below.

Connecting a toolkit (one-time, in the dashboard)

The agent doesn't know about Gmail until you've connected your Composio account to Gmail. This is a one-time human step:

1. Go to https://app.composio.dev/apps
2. Pick a toolkit (Gmail, GitHub, Slack, etc.) → Connect
3. Complete the OAuth flow as the user the agent will act on behalf of (or as a service account for shared workflows)

After this, the toolkit's tools appear in the MCP session and the agent can call them. Composio refreshes tokens automatically; you don't manage them.

The toolkits you've connected are scoped by user_id: a session created with user_id="alice" sees alice's connections, not bob's. This is the multi-tenant primitive.

How Composio tools appear to the agent

Tool names follow MCP conventions — Composio prefixes them by toolkit. Examples:

• GMAIL_SEND_EMAIL
• GITHUB_CREATE_ISSUE
• SLACK_POST_MESSAGE
• NOTION_CREATE_PAGE
• LINEAR_CREATE_ISSUE

The ADK McpToolset wires these into the agent's tool list automatically; your system prompt doesn't need to enumerate them. Claude/the model picks based on the descriptions Composio provides.

If you want only specific toolkits or tools exposed (rather than every connection), you have three options: connect only what the agent should access in the Composio dashboard; scope the session at creation time with create(..., toolkits=..., tools=..., tags=...); or filter client-side with ADK's McpToolset(tool_filter=[...]). See references/composio-patterns.md for both filtering mechanisms.

Multi-tenant patterns — user_id is load-bearing

In a single-tenant agent (you, your tools), COMPOSIO_USER_ID="default" and one set of OAuth connections is fine.

In a multi-tenant deployment (your agent acts on behalf of N end-users), each user needs their own Composio connections so OAuth tokens don't cross users. Two patterns:

1. Per-request user_id (clean, requires harness changes). Don't use the env var. Build the toolset per request, threading the authenticated user's ID:

def get_agent_for_user(end_user_id: str):
    composio = Composio()
    session = composio.create(user_id=end_user_id)
    toolset = McpToolset(
        connection_params=StreamableHTTPConnectionParams(
            url=session.mcp.url, headers=session.mcp.headers,
        )
    )
    return LlmAgent(tools=[*local_tools, toolset], ...)

This means each session has its own connections; user A can't trigger Gmail calls against user B's account. The cost is creating a fresh Composio.create() session per request — usually fine, since session creation is fast.

2. Service-account user_id (simpler, less isolated). Set COMPOSIO_USER_ID="service-account" and connect every toolkit once under that identity. All tenants share one set of connections. Use only when the agent acts on its own data, not on the end-user's.

Cost model

Composio's pricing is per tool execution, not per agent or per session. You're paying for the integrations, not the routing. Check https://composio.dev/pricing for current numbers — there's a generous free tier for prototyping.

The hosted MCP endpoint is free to connect to; you only pay when the agent actually calls a tool.

When NOT to use Composio

Composio is the right answer when the agent needs broad coverage. It's the wrong answer when:

• You only need 1-2 integrations. Writing direct tools for Gmail-only or GitHub-only is less indirection, less cost, and gives you tighter control over rate limiting and error handling. Use Composio when you genuinely need breadth.
• The integration has tight latency requirements. Composio adds an MCP hop (your agent → Composio's MCP server → the third-party API). For most workflows this is irrelevant; for sub-100ms-budget tool calls, write direct.
• You need bespoke business logic on top of the integration. Composio's tools are generic ("send email", "create issue"). If your agent should "send email AND log it in our CRM AND notify Slack," compose those as a custom function tool that calls Composio's tools internally — or skip Composio for that path.
• Compliance / data residency concerns. Composio is a hosted service; tool inputs and outputs flow through their infrastructure. If your data can't leave your boundary, you need self-hosted MCP servers or direct integration.

Common patterns

For deeper patterns — multi-tenant request routing, service-account vs end-user-account models, Composio with --persona agents (where the persona's "skills" can include managing connections), filtering toolkits per agent, and debugging "tool not found" errors — see references/composio-patterns.md.

Quick reference

# Scaffold with Composio
nuvel new my-agent --with-composio --description "..."

# Configure (in .env)
COMPOSIO_API_KEY=ck_...
COMPOSIO_USER_ID=default       # or per-request, see Multi-tenant

# Connect toolkits (one-time, in the dashboard)
# https://app.composio.dev/apps → pick → Connect → OAuth

# Run
python run_adk.py

# To bypass the env-var pattern and create per-user sessions in code:
from composio import Composio
session = Composio().create(user_id=end_user_id)
# Use session.mcp.url and session.mcp.headers in McpToolset