n8n-io/n8n · error · NodeOperationError

Tool name not found in item.json.tool or item.tool

Error message

Tool name not found in item.json.tool or item.tool

What it means

runToolCall reads the tool to invoke from item.json.tool (legacy: item.tool) and found no string value there — the input item does not name a tool, so the MCP tool-call node cannot decide what to call for this item.

Solutions

1. Set a `tool` field (string) on each input item naming an MCP tool
2. Map the upstream data so item.json.tool carries the tool name

When it happens

Trigger: Thrown at packages/@n8n/nodes-langchain/nodes/mcp/shared/runtime.ts:226 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/765f8aab776de58d. Report an issue: GitHub.

Appendix: source

Thrown at packages/@n8n/nodes-langchain/nodes/mcp/shared/runtime.ts:226

/**
 * Run the tool named in `item.json.tool` against the connected client and push
 * the result onto `returnData`. Shared by the cached and non-cached execute paths.
 */
async function runToolCall(opts: {
	ctx: IExecuteFunctions;
	node: INode;
	item: INodeExecutionData;
	mcpTools: McpTool[];
	client: Client;
	timeout: number;
	itemIndex: number;
	returnData: INodeExecutionData[];
}): Promise<void> {
	const { ctx, node, item, mcpTools, client, timeout, itemIndex, returnData } = opts;

	if (!item.json.tool || typeof item.json.tool !== 'string') {
		throw new NodeOperationError(node, 'Tool name not found in item.json.tool or item.tool', {
			itemIndex,
		});
	}

	const toolName = item.json.tool;
	for (const tool of mcpTools) {
		const prefixedName = buildMcpToolName(node.name, tool.name);
		if (toolName !== prefixedName) continue;

		const { tool: _, ...toolArguments } = item.json;
		const schema: JSONSchema7 = tool.inputSchema;
		const sanitizedToolArguments: IDataObject =
			schema.additionalProperties !== true
				? pick(toolArguments, Object.keys(schema.properties ?? {}))
				: toolArguments;

		const result = await client.callTool(
			{ name: tool.name, arguments: sanitizedToolArguments },

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