How to integrate Lexoffice MCP with Pydantic AI

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Introduction

This guide walks you through connecting Lexoffice to Pydantic AI using the Composio tool router. By the end, you'll have a working Lexoffice agent that can generate and send new client invoices, summarize monthly expense reports, list overdue payments from customers through natural language commands.

This guide will help you understand how to give your Pydantic AI agent real control over a Lexoffice account through Composio's Lexoffice MCP server.

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

Also integrate Lexoffice with

TL;DR

Here's what you'll learn:
  • How to set up your Composio API key and User ID
  • How to create a Composio Tool Router session for Lexoffice
  • How to attach an MCP Server to a Pydantic AI agent
  • How to stream responses and maintain chat history
  • How to build a simple REPL-style chat interface to test your Lexoffice workflows

What is Pydantic AI?

Pydantic AI is a Python framework for building AI agents with strong typing and validation. It leverages Pydantic's data validation capabilities to create robust, type-safe AI applications.

Key features include:

  • Type Safety: Built on Pydantic for automatic data validation
  • MCP Support: Native support for Model Context Protocol servers
  • Streaming: Built-in support for streaming responses
  • Async First: Designed for async/await patterns

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

The Lexoffice MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Lexoffice account. It provides structured and secure access to your Lexoffice workspace, so your agent can perform actions like managing invoices, tracking expenses, syncing with bank accounts, and handling client records on your behalf.

  • Invoice creation and management: Effortlessly generate, send, and track invoices, helping you streamline your billing process.
  • Expense tracking and categorization: Let your agent log and classify expenses, making it easy to stay on top of your business spending.
  • Bank integration and reconciliation: Automatically sync transactions with your connected bank accounts for simplified reconciliation and financial oversight.
  • Client and contact management: Manage your customer database, update records, and keep client information organized and up to date.
  • Financial reporting and insights: Generate detailed reports on your business’s financial health, including revenue, expenses, and outstanding balances.

Supported Tools & Triggers

Tools
Create ArticleTool to create a new article (product or service) in Lexoffice.
Create contactTool to create a new contact (customer or vendor) in Lexoffice.
Create Credit NoteTool to create a credit note in Lexoffice.
Create Delivery NoteCreate a delivery note in lexoffice.
Create Event SubscriptionTool to register a new webhook for Lexoffice events.
Create Order ConfirmationTool to create an Order Confirmation in Lexoffice/Lexware.
Create QuotationTool to create a quotation in Lexoffice.
Create VoucherTool to create a bookkeeping voucher in Lexoffice.
Delete ArticleTool to permanently delete an article by its ID.
Delete Event SubscriptionTool to delete an event subscription by its ID.
Download FileDownload a file from lexoffice by its ID.
Get ArticleTool to retrieve an article by ID from Lexoffice.
Get ContactTool to retrieve a specific contact by its ID.
Get Credit NoteTool to retrieve a credit note by its UUID from Lexoffice.
Get Credit Note DocumentTool to render a credit note document (PDF).
Get Delivery NoteTool to retrieve a specific delivery note from Lexoffice by its ID.
Get DunningTool to retrieve a dunning document by its ID.
Get Dunning DocumentTool to render and retrieve a dunning document (PDF) reference.
Get Event SubscriptionTool to retrieve a specific event subscription by its ID.
Get InvoiceTool to retrieve a specific invoice by its UUID.
Get Invoice DocumentTool to render an Invoice Document (PDF) by invoice ID.
Get Order ConfirmationTool to retrieve a specific order confirmation by its ID.
Render Order Confirmation DocumentTool to render an Order Confirmation Document as PDF.
Get Payment InformationTool to retrieve payment information for a specific voucher (invoice or credit note) from Lexoffice.
Get ProfileRetrieves the user and company profile information from Lexoffice.
Get QuotationTool to retrieve a quotation by its ID.
Get Quotation DocumentTool to render a quotation document as a PDF file.
Get VoucherTool to retrieve a specific voucher by its UUID.
List ArticlesTool to list articles from Lexoffice using filters and pagination.
List ContactsTool to retrieve all contacts from Lexoffice with optional filters.
List CountriesTool to retrieve the list of all available countries with tax classifications from Lexoffice.
List Event SubscriptionsTool to retrieve all event subscriptions for the current access token.
List Payment ConditionsTool to retrieve list of currently configured payment conditions from Lexoffice.
List Posting CategoriesTool to retrieve the list of posting categories for bookkeeping vouchers (revenue or expense) supported in lexoffice.
List Print LayoutsTool to retrieve all print layouts for invoices and other documents.
List Recurring TemplatesTool to retrieve all recurring templates from Lexoffice.
List VoucherlistTool to retrieve voucherlist from Lexoffice including bookkeeping vouchers (salesinvoices, salescreditnotes), invoices, credit notes, order confirmations, quotations, and delivery notes.
List VouchersTool to filter vouchers by voucher number from Lexoffice.
Update ArticleTool to update an existing article in Lexoffice with new data.
Update lexoffice contactTool to update an existing contact in lexoffice.
Upload Voucher FileTool to upload and assign files (PDF or image) to a specific voucher in lexoffice.

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:
  • Python 3.9 or higher
  • A Composio account with an active API key
  • Basic familiarity with Python and async programming

Getting API Keys for OpenAI and Composio

OpenAI API Key
  • Go to the OpenAI dashboard and create an API key. You'll need credits to use the models, or you can connect to another model provider.
  • Keep the API key safe.
Composio API Key
  • Log in to the Composio dashboard.
  • Navigate to your API settings and generate a new API key.
  • Store this key securely as you'll need it for authentication.

Install dependencies

bash
pip install composio pydantic-ai python-dotenv

Install the required libraries.

What's happening:

  • composio connects your agent to external SaaS tools like Lexoffice
  • pydantic-ai lets you create structured AI agents with tool support
  • python-dotenv loads your environment variables securely from a .env file

Set up environment variables

bash
COMPOSIO_API_KEY=your_composio_api_key_here
USER_ID=your_user_id_here
OPENAI_API_KEY=your_openai_api_key

Create a .env file in your project root.

What's happening:

  • COMPOSIO_API_KEY authenticates your agent to Composio's API
  • USER_ID associates your session with your account for secure tool access
  • OPENAI_API_KEY to access OpenAI LLMs

Import dependencies

python
import asyncio
import os
from dotenv import load_dotenv
from composio import Composio
from pydantic_ai import Agent
from pydantic_ai.mcp import MCPServerStreamableHTTP

load_dotenv()
What's happening:
  • We load environment variables and import required modules
  • Composio manages connections to Lexoffice
  • MCPServerStreamableHTTP connects to the Lexoffice MCP server endpoint
  • Agent from Pydantic AI lets you define and run the AI assistant

Create a Tool Router Session

python
async def main():
    api_key = os.getenv("COMPOSIO_API_KEY")
    user_id = os.getenv("USER_ID")
    if not api_key or not user_id:
        raise RuntimeError("Set COMPOSIO_API_KEY and USER_ID in your environment")

    # Create a Composio Tool Router session for Lexoffice
    composio = Composio(api_key=api_key)
    session = composio.create(
        user_id=user_id,
        toolkits=["lexoffice"],
    )
    url = session.mcp.url
    if not url:
        raise ValueError("Composio session did not return an MCP URL")
What's happening:
  • We're creating a Tool Router session that gives your agent access to Lexoffice tools
  • The create method takes the user ID and specifies which toolkits should be available
  • The returned session.mcp.url is the MCP server URL that your agent will use

Initialize the Pydantic AI Agent

python
# Attach the MCP server to a Pydantic AI Agent
lexoffice_mcp = MCPServerStreamableHTTP(url, headers={"x-api-key": COMPOSIO_API_KEY})
agent = Agent(
    "openai:gpt-5",
    toolsets=[lexoffice_mcp],
    instructions=(
        "You are a Lexoffice assistant. Use Lexoffice tools to help users "
        "with their requests. Ask clarifying questions when needed."
    ),
)
What's happening:
  • The MCP client connects to the Lexoffice endpoint
  • The agent uses GPT-5 to interpret user commands and perform Lexoffice operations
  • The instructions field defines the agent's role and behavior

Build the chat interface

python
# Simple REPL with message history
history = []
print("Chat started! Type 'exit' or 'quit' to end.\n")
print("Try asking the agent to help you with Lexoffice.\n")

while True:
    user_input = input("You: ").strip()
    if user_input.lower() in {"exit", "quit", "bye"}:
        print("\nGoodbye!")
        break
    if not user_input:
        continue

    print("\nAgent is thinking...\n", flush=True)

    async with agent.run_stream(user_input, message_history=history) as stream_result:
        collected_text = ""
        async for chunk in stream_result.stream_output():
            text_piece = None
            if isinstance(chunk, str):
                text_piece = chunk
            elif hasattr(chunk, "delta") and isinstance(chunk.delta, str):
                text_piece = chunk.delta
            elif hasattr(chunk, "text"):
                text_piece = chunk.text
            if text_piece:
                collected_text += text_piece
        result = stream_result

    print(f"Agent: {collected_text}\n")
    history = result.all_messages()
What's happening:
  • The agent reads input from the terminal and streams its response
  • Lexoffice API calls happen automatically under the hood
  • The model keeps conversation history to maintain context across turns

Run the application

python
if __name__ == "__main__":
    asyncio.run(main())
What's happening:
  • The asyncio loop launches the agent and keeps it running until you exit

Complete Code

Here's the complete code to get you started with Lexoffice and Pydantic AI:

python
import asyncio
import os
from dotenv import load_dotenv
from composio import Composio
from pydantic_ai import Agent
from pydantic_ai.mcp import MCPServerStreamableHTTP

load_dotenv()

async def main():
    api_key = os.getenv("COMPOSIO_API_KEY")
    user_id = os.getenv("USER_ID")
    if not api_key or not user_id:
        raise RuntimeError("Set COMPOSIO_API_KEY and USER_ID in your environment")

    # Create a Composio Tool Router session for Lexoffice
    composio = Composio(api_key=api_key)
    session = composio.create(
        user_id=user_id,
        toolkits=["lexoffice"],
    )
    url = session.mcp.url
    if not url:
        raise ValueError("Composio session did not return an MCP URL")

    # Attach the MCP server to a Pydantic AI Agent
    lexoffice_mcp = MCPServerStreamableHTTP(url, headers={"x-api-key": COMPOSIO_API_KEY})
    agent = Agent(
        "openai:gpt-5",
        toolsets=[lexoffice_mcp],
        instructions=(
            "You are a Lexoffice assistant. Use Lexoffice tools to help users "
            "with their requests. Ask clarifying questions when needed."
        ),
    )

    # Simple REPL with message history
    history = []
    print("Chat started! Type 'exit' or 'quit' to end.\n")
    print("Try asking the agent to help you with Lexoffice.\n")

    while True:
        user_input = input("You: ").strip()
        if user_input.lower() in {"exit", "quit", "bye"}:
            print("\nGoodbye!")
            break
        if not user_input:
            continue

        print("\nAgent is thinking...\n", flush=True)

        async with agent.run_stream(user_input, message_history=history) as stream_result:
            collected_text = ""
            async for chunk in stream_result.stream_output():
                text_piece = None
                if isinstance(chunk, str):
                    text_piece = chunk
                elif hasattr(chunk, "delta") and isinstance(chunk.delta, str):
                    text_piece = chunk.delta
                elif hasattr(chunk, "text"):
                    text_piece = chunk.text
                if text_piece:
                    collected_text += text_piece
            result = stream_result

        print(f"Agent: {collected_text}\n")
        history = result.all_messages()

if __name__ == "__main__":
    asyncio.run(main())

Conclusion

You've built a Pydantic AI agent that can interact with Lexoffice through Composio's Tool Router. With this setup, your agent can perform real Lexoffice actions through natural language. You can extend this further by:
  • Adding other toolkits like Gmail, HubSpot, or Salesforce
  • Building a web-based chat interface around this agent
  • Using multiple MCP endpoints to enable cross-app workflows (for example, Gmail + Lexoffice for workflow automation)
This architecture makes your AI agent "agent-native", able to securely use APIs in a unified, composable way without custom integrations.

How to build Lexoffice MCP Agent with another framework

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Use Lexoffice MCP with Claude Agent SDK

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Use Lexoffice MCP with Codex

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Use Lexoffice MCP with Hermes

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CrewAI

Use Lexoffice MCP with CrewAI

FAQ

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

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

Can I use Tool Router MCP with Pydantic AI?

Yes, you can. Pydantic AI 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 Lexoffice tools.

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

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

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