How to integrate Postgrid MCP with Google ADK

This guide walks you through connecting Postgrid to Google ADK using the Composio tool router. By the end, you'll have a working Postgrid agent that can send a letter to new customer address, verify and standardize a shipping address, create a reusable postcard template through natural language commands. This guide will help you understand how to give your Google ADK agent real control over a Postgrid account through Composio's Postgrid MCP server. Before we dive in, let's take a quick look at the key ideas and tools involved.

Postgrid logoPostgrid
Api Key

Postgrid is an API platform for automating direct mail and address verification. It helps businesses send mail and verify addresses instantly, reducing manual effort and errors.

60 Tools

Introduction

This guide walks you through connecting Postgrid to Google ADK using the Composio tool router. By the end, you'll have a working Postgrid agent that can send a letter to new customer address, verify and standardize a shipping address, create a reusable postcard template through natural language commands.

This guide will help you understand how to give your Google ADK agent real control over a Postgrid account through Composio's Postgrid MCP server.

Before we dive in, let's take a quick look at the key ideas and tools involved.

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TL;DR

Here's what you'll learn:
  • Get a Postgrid account set up and connected to Composio
  • Install the Google ADK and Composio packages
  • Create a Composio Tool Router session for Postgrid
  • Build an agent that connects to Postgrid through MCP
  • Interact with Postgrid using natural language

What is Google ADK?

Google ADK (Agents Development Kit) is Google's framework for building AI agents powered by Gemini models. It provides tools for creating agents that can use external services through the Model Context Protocol.

Key features include:

  • Gemini Integration: Native support for Google's Gemini models
  • MCP Toolset: Built-in support for Model Context Protocol tools
  • Streamable HTTP: Connect to external services through streamable HTTP
  • CLI and Web UI: Run agents via command line or web interface

What is the Postgrid MCP server, and what's possible with it?

The Postgrid MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Postgrid account. It provides structured and secure access to your direct mail and address automation tools, so your agent can verify addresses, send letters, manage contacts, and handle templates for your business communications—all without manual intervention.

  • Automated letter sending: Have your agent create and send physical letters on demand, handling recipient, sender, and content details seamlessly.
  • Contact management: Effortlessly add, update, or delete contacts in your Postgrid account to keep your mailing lists accurate and up to date.
  • Template creation and maintenance: Let your agent generate reusable mail templates with dynamic placeholders, and remove outdated templates as needed.
  • Bank account and payment management: Create or delete bank accounts associated with print and mail services, ensuring smooth financial operations for mail automation.
  • Webhook setup and monitoring: Enable your agent to create or remove webhooks to track events and receive real-time notifications for your mail orders and services.

What is the Composio tool router, and how does it fit here?

What is Composio SDK?

Composio's Composio SDK helps agents find the right tools for a task at runtime. You can plug in multiple toolkits (like Gmail, HubSpot, and GitHub), and the agent will identify the relevant app and action to complete multi-step workflows. This can reduce token usage and improve the reliability of tool calls. Read more here: Getting started with Composio SDK

The tool router generates a secure MCP URL that your agents can access to perform actions.

How the Composio SDK works

The Composio SDK follows a three-phase workflow:

  1. Discovery: Searches for tools matching your task and returns relevant toolkits with their details.
  2. Authentication: Checks for active connections. If missing, creates an auth config and returns a connection URL via Auth Link.
  3. Execution: Executes the action using the authenticated connection.

Step-by-step Guide

Step by step09 STEPS
1

Prerequisites

Before starting, make sure you have:
  • A Google API key for Gemini models
  • A Composio account and API key
  • Python 3.9 or later installed
  • Basic familiarity with Python
2

Getting API Keys for Google and Composio

Google API Key
  • Go to Google AI Studio and create an API key.
  • Copy the key and keep it safe. You will put this in GOOGLE_API_KEY.
Composio API Key and User ID
  • Log in to the Composio dashboard.
  • Go to Settings → API Keys and copy your Composio API key. Use this for COMPOSIO_API_KEY.
  • Decide on a stable user identifier to scope sessions, often your email or a user ID. Use this for COMPOSIO_USER_ID.
3

Install dependencies

bash
pip install google-adk composio python-dotenv

Inside your virtual environment, install the required packages.

What's happening:

  • google-adk is Google's Agents Development Kit
  • composio connects your agent to Postgrid via MCP
  • python-dotenv loads environment variables
4

Set up ADK project

bash
adk create my_agent

Set up a new Google ADK project.

What's happening:

  • This creates an agent folder with a root agent file and .env file
5

Set environment variables

bash
GOOGLE_API_KEY=your-google-api-key
COMPOSIO_API_KEY=your-composio-api-key
COMPOSIO_USER_ID=your-user-id-or-email

Save all your credentials in the .env file.

What's happening:

  • GOOGLE_API_KEY authenticates with Google's Gemini models
  • COMPOSIO_API_KEY authenticates with Composio
  • COMPOSIO_USER_ID identifies the user for session management
6

Import modules and validate environment

python
import os
import warnings

from composio import Composio
from dotenv import load_dotenv
from google.adk.agents.llm_agent import Agent
from google.adk.tools.mcp_tool.mcp_session_manager import StreamableHTTPConnectionParams
from google.adk.tools.mcp_tool.mcp_toolset import McpToolset

load_dotenv()

warnings.filterwarnings("ignore", message=".*BaseAuthenticatedTool.*")

GOOGLE_API_KEY = os.getenv("GOOGLE_API_KEY")
COMPOSIO_API_KEY = os.getenv("COMPOSIO_API_KEY")
COMPOSIO_USER_ID = os.getenv("COMPOSIO_USER_ID")

if not GOOGLE_API_KEY:
    raise ValueError("GOOGLE_API_KEY is not set in the environment.")
if not COMPOSIO_API_KEY:
    raise ValueError("COMPOSIO_API_KEY is not set in the environment.")
if not COMPOSIO_USER_ID:
    raise ValueError("COMPOSIO_USER_ID is not set in the environment.")
What's happening:
  • os reads environment variables
  • Composio is the main Composio SDK client
  • GoogleProvider declares that you are using Google ADK as the agent runtime
  • Agent is the Google ADK LLM agent class
  • McpToolset lets the ADK agent call MCP tools over HTTP
7

Create Composio client and Tool Router session

python
composio_client = Composio(api_key=COMPOSIO_API_KEY)

composio_session = composio_client.create(
    user_id=COMPOSIO_USER_ID,
    toolkits=["postgrid"],
)

COMPOSIO_MCP_URL = composio_session.mcp.url,
print(f"Composio MCP URL: {COMPOSIO_MCP_URL}")
What's happening:
  • Authenticates to Composio with your API key
  • Declares Google ADK as the provider
  • Spins up a short-lived MCP endpoint for your user and selected toolkit
  • Stores the MCP HTTP URL for the ADK MCP integration
8

Set up the McpToolset and create the Agent

python
composio_toolset = McpToolset(
    connection_params=StreamableHTTPConnectionParams(
        url=COMPOSIO_MCP_URL,
        headers={"x-api-key": COMPOSIO_API_KEY}
    )
)

root_agent = Agent(
    model="gemini-2.5-flash",
    name="composio_agent",
    description="An agent that uses Composio tools to perform actions.",
    instruction=(
        "You are a helpful assistant connected to Composio. "
        "You have the following tools available: "
        "COMPOSIO_SEARCH_TOOLS, COMPOSIO_MULTI_EXECUTE_TOOL, "
        "COMPOSIO_MANAGE_CONNECTIONS, COMPOSIO_REMOTE_BASH_TOOL, COMPOSIO_REMOTE_WORKBENCH. "
        "Use these tools to help users with Postgrid operations."
    ),
    tools=[composio_toolset],
)

print("\nAgent setup complete. You can now run this agent directly ;)")
What's happening:
  • Connects the ADK agent to the Composio MCP endpoint through McpToolset
  • Uses Gemini as the model powering the agent
  • Lists exact tool names in instruction to reduce misnamed tool calls
9

Run the agent

bash
# Run in CLI mode
adk run my_agent

# Or run in web UI mode
adk web

Execute the agent from the project root. The web command opens a web portal where you can chat with the agent.

What's happening:

  • adk run runs the agent in CLI mode
  • adk web . opens a web UI for interactive testing

Complete Code

Here's the complete code to get you started with Postgrid and Google ADK:

python
import os
import warnings

from composio import Composio
from composio_google import GoogleProvider
from dotenv import load_dotenv
from google.adk.agents.llm_agent import Agent
from google.adk.tools.mcp_tool.mcp_session_manager import StreamableHTTPConnectionParams
from google.adk.tools.mcp_tool.mcp_toolset import McpToolset

load_dotenv()
warnings.filterwarnings("ignore", message=".*BaseAuthenticatedTool.*")

GOOGLE_API_KEY = os.getenv("GOOGLE_API_KEY")
COMPOSIO_API_KEY = os.getenv("COMPOSIO_API_KEY")
COMPOSIO_USER_ID = os.getenv("COMPOSIO_USER_ID")

if not GOOGLE_API_KEY:
    raise ValueError("GOOGLE_API_KEY is not set in the environment.")
if not COMPOSIO_API_KEY:
    raise ValueError("COMPOSIO_API_KEY is not set in the environment.")
if not COMPOSIO_USER_ID:
    raise ValueError("COMPOSIO_USER_ID is not set in the environment.")

composio_client = Composio(api_key=COMPOSIO_API_KEY, provider=GoogleProvider())

composio_session = composio_client.create(
    user_id=COMPOSIO_USER_ID,
    toolkits=["postgrid"],
)

COMPOSIO_MCP_URL = composio_session.mcp.url


composio_toolset = McpToolset(
    connection_params=StreamableHTTPConnectionParams(
        url=COMPOSIO_MCP_URL,
        headers={"x-api-key": COMPOSIO_API_KEY}
    )
)

root_agent = Agent(
    model="gemini-2.5-flash",
    name="composio_agent",
    description="An agent that uses Composio tools to perform actions.",
    instruction=(
        "You are a helpful assistant connected to Composio. "
        "You have the following tools available: "
        "COMPOSIO_SEARCH_TOOLS, COMPOSIO_MULTI_EXECUTE_TOOL, "
        "COMPOSIO_MANAGE_CONNECTIONS, COMPOSIO_REMOTE_BASH_TOOL, COMPOSIO_REMOTE_WORKBENCH. "
        "Use these tools to help users with Postgrid operations."
    ),  
    tools=[composio_toolset],
)

print("\nAgent setup complete. You can now run this agent directly ;)")

Conclusion

You've successfully integrated Postgrid with the Google ADK through Composio's MCP Tool Router. Your agent can now interact with Postgrid using natural language commands.

Key takeaways:

  • The Tool Router approach dynamically routes requests to the appropriate Postgrid tools
  • Environment variables keep your credentials secure and separate from code
  • Clear agent instructions reduce tool calling errors
  • The ADK web UI provides an interactive interface for testing and development

You can extend this setup by adding more toolkits to the toolkits array in your session configuration.

TOOLS

Supported Tools

Every Postgrid action and event your agent gets out of the box.

Cancel Box

Tool to cancel a box order by its ID.

Cancel Cheque

Tool to cancel a cheque order by its ID.

Cancel Cheque with Note

Tool to cancel a cheque order with a cancellation note.

Cancel Postcard

Tool to cancel a postcard order.

Cancel Postcard With Note

Tool to cancel a postcard order with an optional cancellation note.

Cancel Return Envelope Order

Tool to cancel a return envelope order.

CREATE_BANK_ACCOUNT

Tool to create a new bank account for print & mail service.

Create Box

Tool to create a box mailing order for letters with plastic cards or cheques.

Create Cheque

Tool to create a cheque order for physical cheque mailing.

Create Contact

Tool to create a new contact in PostGrid.

Create Letter

Tool to create and send a letter via PostGrid.

Create Postcard

Tool to create and send a postcard via PostGrid.

Create Return Envelope

Tool to create a return envelope for mail recipients to respond.

Create Return Envelope Order

Tool to create a batch order of return envelopes to be printed and delivered.

Create Template

Tool to create a new mail template in PostGrid.

Create Template Editor Session

Tool to create a template editor session for interactive template editing.

Create Tracker

Tool to create a tracker for monitoring mail delivery status via URL tracking.

Create Webhook

Tool to create a new webhook to receive order event notifications.

Delete Bank Account

Tool to delete a bank account by its ID.

Delete Contact

Tool to delete a contact by its ID.

Delete Template

Tool to delete a template by its ID.

Delete Template Editor Session

Tool to delete a template editor session by its ID.

Delete Tracker

Tool to delete a tracker by its ID.

Delete Webhook

Tool to delete a webhook subscription.

Fill Test Return Envelope Order

Tool to fill a test return envelope order for testing purposes.

Get Bank Account

Tool to retrieve a bank account.

Get Box

Tool to retrieve a specific box order by ID.

Get Cheque

Tool to retrieve a specific cheque by ID.

Get Contact

Tool to retrieve a contact.

Get Letter

Tool to retrieve a letter.

Get Postcard

Tool to retrieve a specific postcard by ID.

Get Return Envelope

Tool to retrieve a return envelope.

Get Return Envelope Order

Tool to retrieve a specific return envelope order.

Get Template

Tool to retrieve a template.

Get Tracker

Tool to retrieve a tracker.

Get Webhook

Tool to retrieve details of a specific webhook by its ID.

List Bank Accounts

Tool to list bank accounts.

List Box Orders

Tool to list box orders.

List Cheques

Tool to list cheques with optional filters and pagination.

List Contacts

Tool to list contacts.

List Webhook Events

Tool to retrieve a list of webhook events with optional pagination.

List Letters

Tool to list letters.

List Postal Statements

Tool to list all postal statements for billing and tracking purposes.

List Postcards

Tool to retrieve a list of postcards with optional filtering and pagination.

List Return Envelope Orders

Tool to list all return envelope orders for a specific return envelope.

List Return Envelopes

Tool to list return envelopes.

List Self-Mailers

Tool to list self-mailers.

List Sub-Organizations

Tool to list sub-organizations.

List Template Editor Sessions

Tool to list template editor sessions.

List Templates

Tool to list templates.

List Trackers

Tool to list all trackers.

List Tracker Visits

Tool to list all visits for a tracker.

List Webhook Invocations

Tool to list previous invocations of a webhook with response status codes.

List Webhooks

Tool to retrieve a list of configured webhooks with optional filtering and pagination.

Progress Test Box

Tool to progress a test box through processing stages for webhook testing.

Progress Test Cheque

Tool to progress a test cheque through processing stages for webhook testing.

Progress Test Postcard

Tool to progress a test postcard through processing stages for webhook testing.

Update Template

Tool to update an existing mail template in PostGrid.

Update Tracker

Tool to update an existing tracker's redirect URL template and/or expiration settings.

Update Webhook

Tool to update an existing webhook configuration.

FAQ

Frequently asked questions

With a standalone Postgrid MCP server, the agents and LLMs can only access a fixed set of Postgrid tools tied to that server. However, with the Composio Tool Router, agents can dynamically load tools from Postgrid and many other apps based on the task at hand, all through a single MCP endpoint.

Yes, you can. Google ADK fully supports MCP integration. You get structured tool calling, message history handling, and model orchestration while Tool Router takes care of discovering and serving the right Postgrid tools.

Yes, absolutely. You can configure which Postgrid scopes and actions are allowed when connecting your account to Composio. You can also bring your own OAuth credentials or API configuration so you keep full control over what the agent can do.

All sensitive data such as tokens, keys, and configuration is fully encrypted at rest and in transit. Composio is SOC 2 Type 2 compliant and follows strict security practices so your Postgrid data and credentials are handled as safely as possible.

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