Build an MCP Server in n8n: Google Calendar + Custom Functions Dual-Service Example

Import template → Configure two MCP servers (Google Calendar tools + custom function sub-workflows) → Connect via MCP Clients to an AI Agent → Interact through chat trigger

Who

Operators already running n8n 1.88.0+ who want to extend their AI Agent's tool set using the MCP protocol

You get

A working setup that exposes both Google Calendar operations (search/create/update/delete events) and custom functions (text case conversion, random user data, fetch jokes) as MCP servers, with an AI Agent auto-discovering and calling them through MCP Clients

You need

n8n · MCP Trigger · MCP Client · Google Calendar · Sub-workflow

Steps

1. Import template and understand the architecture

   Import 'Build an MCP server with Google Calendar and custom functions' from the n8n template library. Architecture overview: left side is the AI Agent conversation entry (Chat Trigger + AI Agent + OpenAI 4o + Simple Memory); middle layer has two MCP Clients (Calendar MCP / My Functions); right side hosts two MCP Trigger servers (Google Calendar MCP / My Functions Server) with their respective tool nodes underneath.

2. Activate the workflow and obtain MCP server URLs

   Activate the workflow. Open the two MCP Trigger nodes (Google Calendar MCP, My Functions Server) and copy their Production URLs (typically https://your-n8n-domain/mcp/{path}/sse). These URLs will be used in the next step to configure the MCP Clients.

   Setup guidance · Source text。Sticky Note next to MCP Trigger nodes; operational instruction

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   ## Activate the workflow to make the MCP Trigger work
   In order to make the MCP server available, you need to activate the workflow.
   
   Then copy the Production URL of the MCP Trigger and paste it in the corresponding MCP Client tool.

3. Configure MCP Client endpoints

   Open the Calendar MCP and My Functions MCP Client nodes. Paste the corresponding Production URLs from the previous step into the sseEndpoint field. The template uses placeholder addresses https://n8n.yourdomain/mcp/my-calendar/sse and https://n8n.yourdomain/mcp/my-functions/sse; replace these with your actual domain and path.

   Setup guidance · Source text。Sticky Note next to MCP Client nodes; configuration instruction

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   ## MCP Clients
   For every tool here you need to obtain he corresponding Production URL from the MCP Triggers on the right 👉

4. Configure Google Calendar credentials and tool parameters

   The Google Calendar MCP server hosts four Google Calendar Tool nodes: SearchEvent, CreateEvent, UpdateEvent, and DeleteEvent. Each requires Google Calendar OAuth credentials. The calendar field defaults to [email protected]; replace it with your actual calendar ID. Tool parameters use $fromAI() and are auto-filled by the AI Agent; no manual fixing needed.

   Setup guidance · Source text。Sticky Note in Google Calendar tools area; credential guidance

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   ## Google Calendar tools require credentials
   If you don't have your Google Credentials set up in n8n yet, watch [this](https://www.youtube.com/watch?v=3Ai1EPznlAc) video to learn how to do it.
   
   If you are using n8n Cloud plans, it's very intuitive to setup and you may not even need the tutorial.

5. Review the custom function sub-workflow

   The My Functions Server exposes three toolWorkflow nodes through its MCP Trigger: Convert Text (case conversion), Generate random user data, and Random Jokes. These tools call an internal sub-workflow segment within the same workflow: triggered by 'When Executed by Another Workflow', routed by a Switch node based on function_name to the appropriate branch (uppercase / lowercase / random_user_data / joke). The sub-workflow receives a payload parameter and returns results. No changes are required for basic use.

   Setup guidance · Source text。Sticky Note in sub-workflow area; architecture explanation

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   ## The My Functions MCP calls this sub-workflow every time.
   A subworkflow is a separate workflow that can be called by other workflows and is able to receive parameters.
   Learn more about sub-workflows **[here](https://docs.n8n.io/flow-logic/subworkflows/)**

6. Configure the AI Agent and model

   The AI Agent node uses OpenAI 4o (gpt-4o) as the language model. Its System Message is: '=You are a helpful assistant.\nCurrent datetime is {{ $now.toString() }}'. Simple Memory provides conversational context. Chat Trigger is the default chat entry. Author note: 4o-mini struggled with calendar requests in testing, while 4o handled them smoothly; 4o-mini may work but requires further validation.

   Execution prompt · Source text。AI Agent node systemMessage field

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   =You are a helpful assistant.
   Current datetime is {{ $now.toString() }}

   Setup guidance · Source text。Sticky Note next to OpenAI 4o node; model selection note

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   ## Why model 4o? 👆
   After testing 4o-mini it had some difficulties handling the calendar requests, while the 4o model handled it with ease.
   
   Depending on your prompt and tools, 4o-mini might be able to work well too, but it requires further testing.

7. Test the setup

   [First-test safety] Before sending the examples below, use a dedicated test calendar (change the calendar field), or disconnect CreateEvent / UpdateEvent / DeleteEvent first; only reconnect a real calendar after tool calls look correct. Send example requests through the Chat Trigger to verify both MCP services. Custom function examples: 'Use your tools to convert this text to lower case: EXAMPLE TeXt', 'Generate 5 random user data', 'Please obtain 3 jokes'. Calendar examples: 'What is my schedule for next week?', 'I have a meeting with John tomorrow at 2pm. Please add it to my Calendar.', 'Cancel my meeting with John, tomorrow.' Observe whether the AI Agent correctly invokes the corresponding tools and returns results.

   Execution prompt · Source text。Sticky Note in Chat Trigger area; test examples list

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   # Try these example requests with the AI Agent
   
   ### My Functions MCP
   1. Use your tools to convert this text to lower case: `EXAMPLE TeXt`
   
   2. Use your tools to convert this text to upper case: `example TeXt`
   
   3. Generate 5 random user data, please.
   
   4. Please obtain 3 jokes.
   
   
   
   
   ### Calendar MCP
   5. What is my schedule for next week?
   
   6. I have a meeting with John tomorrow at 2pm. Please add it to my Calendar.
   
   7. Adjust the time of my meeting with John tomorrow from 2pm to 4pm, please.
   
   8. Cancel my meeting with John, tomorrow.

You are an n8n workflow setup assistant. The user wants to reproduce the 'Build an MCP server with Google Calendar and custom functions' template. Assist in this order:
1. Confirm the user's n8n version is ≥ 1.88.0 and their instance is reachable to generate Production URLs.
2. Guide them to import the template and identify the three areas: AI Agent (left), MCP Clients (middle), MCP Servers (right).
3. Help activate the workflow, obtain the two MCP Trigger Production URLs, and paste them into the corresponding MCP Client sseEndpoint fields.
4. Remind them to configure Google Calendar OAuth credentials and replace the calendar field with a real calendar ID.
5. Explain the custom function sub-workflow Switch routing logic and confirm no changes are needed.
6. Provide the 8 test examples for verification. If invocations fail, check URL reachability, credential validity, and model quota.