Describe the problem/error/question
Using N8N workflow v 191.2
Creating an MCP that takes as an input a timestamp: “2025-07-10T15:00:00.000Z”
What is the error message (if any)?
langchain_core.tools.base.ToolException: Error: Received tool input did not match expected schema
Please share your workflow
{
“nodes”: [
{
“parameters”: {
“path”: “e2e77286-9055-4eec-96b9-8b8e85d60ae8”
},
“type”: “@n8n/n8n-nodes-langchain.mcpTrigger”,
“typeVersion”: 1,
“position”: [
-580,
-960
],
“id”: “91a44b19-b0e2-4592-960c-832e922adf40”,
“name”: “MCP Server Trigger”,
“webhookId”: “e2e77286-9055-4eec-96b9-8b8e85d60ae8”
},
{
“parameters”: {
“toolDescription”: “Makes an POST HTTP request on api.cal.com/v1/bookings and returns the response data”,
“method”: “POST”,
“url”: “https://test.com”,
“authentication”: “predefinedCredentialType”,
“nodeCredentialType”: “calApi”,
“sendQuery”: true,
“queryParameters”: {
“parameters”: [
{
“name”: “apiKey”,
“value”: “cal_live_7f183a27a9bfa15d3a606f2c4733de95”
}
]
},
“sendBody”: true,
“bodyParameters”: {
“parameters”: [
{
“name”: “eventTypeId”,
“value”: “={{ /n8n-auto-generated-fromAI-override/ $fromAI(‘parameters0_Value’, 1. Map the user’s choice (parsed from \\userInputText\) to \\eventTypeId\ (as a number):\n\n * \"Argentina\" → 2497888\n * \"México\" → 2510264\n * \"Yoshi\" → 2743704, ‘string’) }}”
},
{
“name”: “=start”,
“value”: “={{ $fromAI(‘parameters1_Value’, ‘Extract the start date and time. It MUST be a string formatted as a full ISO 8601 timestamp, including the UTC timezone designator \‘Z\’. Example: \‘2025-07-10T15:00:00.000Z\’’, ‘string’) }}”
},
{
“name”: “=responses.userFullName”,
“value”: “={{ /n8n-auto-generated-fromAI-override/ $fromAI(‘parameters2_Value’, the user full name, ‘string’) }}”
},
{
“name”: “=responses.userEmail”,
“value”: “={{ /n8n-auto-generated-fromAI-override/ $fromAI(‘parameters3_Value’, the user email, ‘string’) }}”
},
{
“name”: “userTimeZone”,
“value”: “={{ /n8n-auto-generated-fromAI-override/ $fromAI(‘parameters4_Value’, Determine JSON.timeZone based on the chosen eventTypeId:\n\n * If \\eventTypeId\ is 2497888, use the Argentina IANA timezone (e.g., \"America/Argentina/Buenos\\\\_Aires\").\n * If \\eventTypeId\ is 2510264, use the Mexico IANA timezone (e.g., \"America/Mexico\\\\_City\")., ‘string’) }}”
},
{
“name”: “language”,
“value”: “es”
},
{
“name”: “=metadata.source”,
“value”: “={{ /n8n-auto-generated-fromAI-override/ $fromAI(‘parameters6_Value’, The user phone number, ‘string’) }}”
}
]
},
“options”: {}
},
“type”: “n8n-nodes-base.httpRequestTool”,
“typeVersion”: 4.2,
“position”: [
-1120,
-1000
],
“id”: “12caf749-753a-4c92-b6d1-4a1be6db56be”,
“name”: “POST Creates a new booking new”,
“credentials”: {
“calApi”: {
“id”: “fJNCZ5KPAECUtj77”,
“name”: “Cal account - Product Team API”
}
}
}
],
“connections”: {
“POST Creates a new booking new”: {
“ai_tool”: [
[
{
“node”: “MCP Server Trigger”,
“type”: “ai_tool”,
“index”: 0
}
]
]
}
},
“pinData”: {},
“meta”: {
“instanceId”: “55571e92873dad1c313e1ff5d9be1cdca5978f8aafda74504a91ad01a64bf0c0”
}
}
Input sent to the server
{‘parameters4_Value’: ‘America/Mexico_City’, ‘parameters3_Value’: ‘[email protected]’, ‘parameters6_Value’: ‘48-1663-wa-default’, ‘parameters0_Value’: 2510264, ‘parameters2_Value’: ‘Rafael Lima’, ‘parameters1_Value’: ‘2025-07-10T15:00:00.000Z’}
What have I discovered:
- All fields work properly except for the one called “start” which expects a timestamp
- The input value is a string, but somehow is being blocked by the schema validator
This is the field description
I believe for some reason N8N is identifying as a timestamp and not accepting it as a string. Could it be a bug? Any solutions?
Information on your n8n setup
- n8n version:
- Database (default: SQLite):
- n8n EXECUTIONS_PROCESS setting (default: own, main):
- Running n8n via (n8n cloud:
