How to integrate Brex MCP with Google ADK

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Introduction

This guide walks you through connecting Brex to Google ADK using the Composio tool router. By the end, you'll have a working Brex agent that can create a new card for our intern, get the latest account statement pdf, add an expense for last week's conference through natural language commands.

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

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

Also integrate Brex with

TL;DR

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

The Brex MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Brex account. It provides structured and secure access to your company's financial tools, so your agent can perform actions like managing cards, tracking expenses, creating budgets, and retrieving account details on your behalf.

  • Card creation and management: Instantly issue new cards, assign them to users or vendors, and control spending limits via your agent.
  • Automated expense tracking: Let your agent create and log expenses, helping you keep company finances organized and up to date.
  • Budget and department setup: Quickly create budgets for teams or projects and set up new departments without manual effort.
  • Account and statement retrieval: Fetch detailed account information and download statements whenever you need financial insights or records.
  • User and location management: Add new users or locations to your Brex account, making it easy to scale as your business grows.

Supported Tools & Triggers

Tools
Add Webhook Group MembersAdd webhook subscription members to a webhook group.
Archive BudgetArchive a budget to mark it as inactive and prevent future expenses.
Archive Spend LimitArchive a spend limit in Brex.
Create BudgetCreate a new budget for departments or projects.
Create Spend Limit (Budget V1)Tool to create a new Spend Limit (Budget) in Brex.
Create CardCreate a new card and assign it to a user.
Create DepartmentCreate a new department.
Create Document Upload for ReferralCreate a document upload URL for a referral and return a pre-signed S3 upload URL.
Create ExpenseCreate a new expense.
Create Custom FieldCreate a new custom field in Brex.
Create Field ValuesCreate custom field values for a specific Brex field.
Create LocationCreate a new location.
Create Referral RequestTool to create a new referral to Brex for onboarding.
Create Spend LimitTool to create a spend limit in Brex.
Create Job TitleCreate a new job title.
Create UserCreate a new user in the Brex account.
Create VendorCreate a new vendor in Brex for payment operations.
Create Webhook GroupTool to create a webhook group for targeting webhook subscriptions.
Create Webhook SubscriptionRegister a new webhook subscription to receive real-time notifications for Brex events.
Delete FieldTool to delete a custom field by Brex ID.
Delete Field ValuesDelete custom field values for a specific field.
Delete VendorDelete a vendor by ID.
Get Account StatementsGet finalized statements for the primary cash account.
Get Budget DetailsGet detailed information about a specific budget.
Get Card DetailsGet detailed information about a specific card.
Get Card ExpenseTool to retrieve detailed information about a specific card expense by its ID.
Get Card NumberGet card number, CVV, and expiration date for a specific card.
Get Card TransactionsGet settled card transactions for the primary card account.
Get Company Cash AccountsRetrieve all cash (deposit) accounts for the company.
Get Company DetailsGet company information associated with the OAuth2 access token.
Get Department By IDGet detailed information about a specific department by ID.
Get ExpenseTool to get details of a specific expense by ID.
Get Field By IDTool to retrieve a custom field by its Brex ID.
Get Field Value By IDTool to retrieve a specific field value by field ID and field value ID.
Get Legal EntityTool to retrieve a legal entity by its ID from Brex.
Get Location By IDGet detailed information about a specific location by ID.
Get Referral By IDTool to retrieve a specific referral by its ID from Brex.
Get Spend Limit By IDTool to get detailed information about a specific spend limit by its ID.
Get Spend LimitsGet spend limits configuration.
Get Title by IDGet detailed information about a specific job title by ID.
Get Transaction by IDGet details of a specific transaction by ID.
Get Card TransactionsGet card transactions from the primary Brex account.
Get Transactions by Amount RangeGet card transactions filtered by amount range and date period.
Search Transactions by DescriptionSearch and filter card transactions by description text.
Get User LimitRetrieves the monthly spending limit and available balance for a specific Brex user.
Get User ProfileGet user profile information from Brex Team API.
Get Vendor By IDTool to get vendor details by ID.
Get Webhook GroupTool to retrieve details of a specific webhook group by ID.
Get Webhook SubscriptionTool to retrieve details of a specific webhook subscription by ID.
List Budget ProgramsTool to list all budget programs in the organization.
List BudgetsList all budgets and show available amounts across all cards.
List Card AccountsTool to list all card accounts for the company.
List CardsList all cards associated with the account.
List Card StatementsTool to list finalized statements for primary card accounts.
List DepartmentsList all departments in the organization.
List ExpensesTool to list expenses from the Brex platform.
List Field ValuesTool to list values under a custom field.
List Legal EntitiesTool to list all legal entities in the Brex account with pagination support.
List LocationsList all locations in the organization.
List ReferralsTool to list all referrals created in the Brex account.
List Job TitlesList all job titles in the organization.
List TransfersLists transfers for the account.
List TripsLists trips according to the filters passed in the query string.
List UsersList all users in the Brex account.
List VendorsList all vendors.
List Webhook Group MembersTool to list all members of a webhook group.
List Webhook GroupsTool to list all webhook groups.
List Webhook SecretsTool to retrieve webhook signing secrets for validating incoming webhook messages from Brex.
List Webhook SubscriptionsTool to list all registered webhook subscriptions.
Create Receipt MatchCreates a receipt match request and returns a pre-signed S3 upload URI.
Create Receipt Upload for ExpenseCreates a receipt upload request for a specific card expense and returns a pre-signed S3 upload URL.
Set User LimitSet or update the monthly spending limit for a Brex user.
Transfer CardTransfer a card to a different user.
Update BudgetUpdate an existing budget's configuration in Brex.
Update Spend Limit (V1)Tool to update a Spend Limit (budget) using the v1 API.
Update Card LimitsUpdate spending limits and controls for a Brex card.
Update Card StatusUpdate the status of a Brex card by locking, unlocking, or terminating it.
Update ExpenseTool to update an expense by its ID.
Update FieldTool to update a custom field in Brex.
Update Field ValuesTool to update custom field values in Brex for a specific field.
Update Spend LimitUpdates an existing Brex spend limit by its ID.
Update UserUpdate user details.
Update VendorTool to update vendor information in Brex.
Update Webhook SubscriptionUpdates an existing Brex webhook subscription's configuration.

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

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

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.

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 Brex via MCP
  • python-dotenv loads environment variables

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

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

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

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=["brex"],
)

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

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 Brex 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

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 Brex 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=["brex"],
)

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

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

Conclusion

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

Key takeaways:

  • The Tool Router approach dynamically routes requests to the appropriate Brex 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.

How to build Brex MCP Agent with another framework

FAQ

What are the differences in Tool Router MCP and Brex MCP?

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

Can I use Tool Router MCP with Google ADK?

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 Brex tools.

Can I manage the permissions and scopes for Brex while using Tool Router?

Yes, absolutely. You can configure which Brex 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.

How safe is my data with Composio Tool Router?

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 Brex data and credentials are handled as safely as possible.

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DataStax
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Context
Letta
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HubSpot
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Altera
DataStax
Entelligence
Rolai

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