How to integrate MailerCheck MCP with Google ADK

This guide walks you through connecting MailerCheck to Google ADK using the Composio tool router. By the end, you'll have a working MailerCheck agent that can verify email addresses, create verification lists, review results, and check your credit balance through natural language commands. This guide will help you understand how to give your Google ADK agent real control over a MailerCheck account through Composio's MailerCheck MCP server. Before we dive in, let's take a quick look at the key ideas and tools involved.

Get started for freeGet a demo
MailerCheck logoMailerCheck
Api Key

MailerCheck is an email verification service for checking addresses and lists. It helps protect sender reputation by reducing bounces and bad contacts.

9 Tools

Introduction

This guide walks you through connecting MailerCheck to Google ADK using the Composio tool router. By the end, you'll have a working MailerCheck agent that can verify email addresses, create verification lists, review results, and check your credit balance through natural language commands.

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

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

Also integrate MailerCheck with

OpenAI Agents SDKClaude Agent SDKClaude CodeClaude CoworkCodexOpenClawHermesCLILangChainVercel AI SDKMastra AILlamaIndexCrewAI

TL;DR

Here's what you'll learn:
  • Get a MailerCheck account set up and connected to Composio
  • Install the Google ADK and Composio packages
  • Create a Composio Tool Router session for MailerCheck
  • Build an agent that connects to MailerCheck through MCP
  • Interact with MailerCheck 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 MailerCheck MCP server, and what's possible with it?

The MailerCheck MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your MailerCheck account. It provides structured and secure access to email verification, verification lists, results, and account details, so your agent can verify individual addresses, create and run list checks, review results, manage lists, and monitor verification credits on your behalf.

  • Individual email verification: Have your agent verify a specific email address before you add it to a campaign or contact database.
  • Bulk list verification: Let the agent create a named list of email addresses and start checking every address in it.
  • Verification status and results: Direct your agent to review a list's progress, summary statistics, and email-level results, including results filtered by classification.
  • Verification list management: Instruct your agent to browse existing verification lists, inspect a chosen list, or permanently delete one you no longer need.
  • Account and credit checks: Have your agent confirm the connected MailerCheck account and report the current verification-credit balance.

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 MailerCheck 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=["mailercheck"],
)

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 MailerCheck 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 MailerCheck 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=["mailercheck"],
)

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 MailerCheck operations."
    ),  
    tools=[composio_toolset],
)

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

Conclusion

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

Key takeaways:

  • The Tool Router approach dynamically routes requests to the appropriate MailerCheck 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 MailerCheck action and event your agent gets out of the box.

Create Verification List

Create a MailerCheck verification list by ingesting a name and email-address array.

Delete Verification List

Permanently and irreversibly delete a MailerCheck verification list by ID.

Get Credit Balance

Return the current MailerCheck verification-credit balance.

Get Current Account

Return the connected MailerCheck user and account identity.

Get Verification List

Return one verification list, including its status, item count, verification timing, and aggregate result statistics.

List Verification Lists

Return one page of verification lists for the connected MailerCheck account, with an opaque cursor when another provider-controlled page exists.

List Verification Results

Return one page of email-level results for a verification list, optionally filtered by classification.

Start List Verification

Irreversibly start verification of every address in a MailerCheck list.

Verify Email

Consumes exactly one MailerCheck verification credit on every successful call.

FRAMEWORKS

How to build MailerCheck MCP Agent with another framework

OpenAI Agents SDK logo

OpenAI Agents SDK

Use MailerCheck MCP with OpenAI Agents SDK

Claude Agent SDK logo

Claude Agent SDK

Use MailerCheck MCP with Claude Agent SDK

Claude Code logo

Claude Code

Use MailerCheck MCP with Claude Code

Claude Cowork logo

Claude Cowork

Use MailerCheck MCP with Claude Cowork

Codex logo

Codex

Use MailerCheck MCP with Codex

OpenClaw logo

OpenClaw

Use MailerCheck MCP with OpenClaw

Hermes logo

Hermes

Use MailerCheck MCP with Hermes

CLI logo

CLI

Use MailerCheck MCP with CLI

LangChain logo

LangChain

Use MailerCheck MCP with LangChain

Vercel AI SDK logo

Vercel AI SDK

Use MailerCheck MCP with Vercel AI SDK

Mastra AI logo

Mastra AI

Use MailerCheck MCP with Mastra AI

LlamaIndex logo

LlamaIndex

Use MailerCheck MCP with LlamaIndex

CrewAI logo

CrewAI

Use MailerCheck MCP with CrewAI

FAQ

Frequently asked questions

With a standalone MailerCheck MCP server, the agents and LLMs can only access a fixed set of MailerCheck tools tied to that server. However, with the Composio Tool Router, agents can dynamically load tools from MailerCheck 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 MailerCheck tools.

Yes, absolutely. You can configure which MailerCheck 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 MailerCheck data and credentials are handled as safely as possible.

Start with MailerCheck.It takes 30 seconds.

Managed auth, hosted MCP servers, and every MailerCheck tool your agent needs.Free to start.

Start building
Customer stories

Teams ship real agents on Composio

GET STARTED FOR FREEBOOK A DEMO
agent.aiZoomLettaGleanHubSpotAWSWabi

Karan skipped his own birthday party to fix our critical issue. It was 10pm and he diverted his Waymo to help us instead. This really sets the bar — it shows the commitment you need when users rely on your software.

Harsha Gaddipati
Harsha Gaddipati
Co-founder, Slashy

A lot of students tell us that the moment their connected tools start talking to each other inside Opennote feels almost magical. The agent just knows them, and it's immensely helped keep new users on the platform.

Abhi Arya
Abhi Arya
Co-founder, Opennote

We chose Composio over Pipedream because it delivered depth where it mattered — niche tools and tricky edge cases other platforms simply ignored. That gave us confidence to scale without compromising.

Nirman Dave
Nirman Dave
CEO, Zams

As a solo builder, shipping fast is life or death. The only way I can outcompete incumbents is by outmanoeuvring them. Getting bogged down managing agent auth would have been a death sentence.

Ryan Yu
Ryan Yu
Founder, Extra Thursday

Before Composio, adding tool integrations was slow and resource-intensive. Each one could take weeks of engineering time, and maintaining them meant constantly keeping up with API changes.

Tomisin Jenrola
Tomisin Jenrola
Founder & CEO, SwarmZero

With hands-on help from their founder, we integrated Gmail and Google Drive in just 30 minutes. This level of personal support and commitment is exactly what startups should strive for.

Jerome Leclanche
Jerome Leclanche
Co-Founder, Ingram Technologies