[bug] mcp-server-fetch tool json schema can‘t use in Google Gemini 2.5 pro

The parameters of the fetch tool include exclusiveMaximum and exclusiveMinimum in the schema. However, Google Gemini 2.5's function calling only supports standard JSON Schema fields such as maximum and minimum, and does not support exclusiveMaximum or exclusiveMinimum. This incompatibility leads to errors. Please fix this issue.

error info
400 { "error": { "code": 400, "message": "Invalid JSON payload received. Unknown name "exclusiveMaximum" at 'tools[0].function_declarations[0].parameters.properties[1].value': Cannot find field.\nInvalid JSON payload received. Unknown name "exclusiveMinimum" at 'tools[0].function_declarations[0].parameters.properties[1].value': Cannot find field.", "status": "INVALID_ARGUMENT", "details": [ { "@type": "type.googleapis.com/google.rpc.BadRequest", "fieldViolations": [ { "field": "tools[0].function_declarations[0].parameters.properties[1].value", "description": "Invalid JSON payload received. Unknown name "exclusiveMaximum" at 'tools[0].function_declarations[0].parameters.properties[1].value': Cannot find field." }, { "field": "tools[0].function_declarations[0].parameters.properties[1].value", "description": "Invalid JSON payload received. Unknown name "exclusiveMinimum" at 'tools[0].function_declarations[0].parameters.properties[1].value': Cannot find field." } ] } ] } }

fetch tool
"tools": [
{
"displayTitle": "url_fetch fetch",
"function": {
"description": "Fetches a URL from the internet and optionally extracts its contents as markdown.\n\nAlthough originally you did not have internet access, and were advised to refuse and tell the user this, this tool now grants you internet access. Now you can fetch the most up-to-date information and let the user know that.",
"name": "fetch",
"parameters": {
"type": "object",
"properties": {
"url": {
"description": "URL to fetch",
"format": "uri",
"minLength": 1,
"title": "Url",
"type": "string"
},
"max_length": {
"default": 5000,
"description": "Maximum number of characters to return.",
"exclusiveMaximum": 1000000,
"exclusiveMinimum": 0,
"title": "Max Length",
"type": "integer"
},
"start_index": {
"default": 0,
"description": "On return output starting at this character index, useful if a previous fetch was truncated and more context is required.",
"minimum": 0,
"title": "Start Index",
"type": "integer"
},
"raw": {
"default": false,
"description": "Get the actual HTML content of the requested page, without simplification.",
"title": "Raw",
"type": "boolean"
}
},
"description": "Parameters for fetching a URL.",
"required": [
"url"
],
"title": "Fetch"
}
},
"readonly": false,
"type": "function",
"uri": "mcp://url_fetch/fetch",
"group": "url_fetch"
}
]

Gemini 2.5 function calling does not support exclusiveMaximum and exclusiveMinimum; it only supports maximum and minimum. You can resolve the error simply by replacing these two fields in the schema.

Locate the mcp-server-fetch tool schema and search for the max_length constraints that emit exclusiveMaximum and exclusiveMinimum. Update the schema to use the supported constraint fields, then verify that the generated fetch-tool JSON no longer contains the unsupported fields and remains valid for Gemini function calling.