n8n-io/n8n · error · ValidationError

VALIDATION_ERROR

VALIDATION_ERROR

Error message

Invalid connection parameters

What it means

Zod schema validation failed on the input passed to connect_nodes. The schema (nodeConnectionSchema) requires sourceNodeId and targetNodeId as strings; sourceOutputIndex and targetInputIndex are optional numbers. Any deviation throws a ZodError which the catch block relabels as VALIDATION_ERROR with the original issue list in details.

Source

Thrown at packages/@n8n/ai-workflow-builder.ee/src/tools/connect-nodes.tool.ts:290

					},
				};
				reporter.complete(output);

				// Return success with state updates
				const stateUpdates = updateWorkflowConnections(newConnection);
				return createSuccessResponse(config, message, stateUpdates);
			} catch (error) {
				// Handle validation or unexpected errors
				let toolError;

				if (error instanceof z.ZodError) {
					const validationError = new ValidationError('Invalid connection parameters', {
						field: error.errors[0]?.path.join('.'),
						value: error.errors[0]?.message,
					});
					toolError = {
						message: validationError.message,
						code: 'VALIDATION_ERROR',
						details: error.errors,
					};
				} else {
					toolError = {
						message: error instanceof Error ? error.message : 'Unknown error occurred',
						code: 'EXECUTION_ERROR',
					};
				}

				reporter.error(toolError);
				return createErrorResponse(config, toolError);
			}
		},
		{
			name: CONNECT_NODES_TOOL.toolName,
			description: `Connect two nodes in the workflow. The tool automatically determines the connection type based on node capabilities and ensures correct connection direction.

UNDERSTANDING CONNECTIONS:

View on GitHub (pinned to 5ac6606e81)

Solutions

1. Read details (the ZodError.issues array) to find the first failing path and message.
2. Ensure sourceNodeId and targetNodeId are UUID strings and indices are numbers or omitted.
3. Re-invoke connect_nodes with corrected input.

Example fix

// before
connect_nodes.invoke({ sourceNodeId: { id: 'abc' }, targetNodeId: 'def' });
// after
connect_nodes.invoke({ sourceNodeId: 'abc-1234', targetNodeId: 'def-5678' });

import { nodeConnectionSchema } from '@/tools/connect-nodes.tool';

// Validate input with the same schema before invoking the tool.
const parsed = nodeConnectionSchema.safeParse(input);
if (!parsed.success) {
  // surface parsed.error.issues to the caller / LLM and skip the tool call
}

function isValidConnectInput(v: unknown): v is { sourceNodeId: string; targetNodeId: string; sourceOutputIndex?: number; targetInputIndex?: number } {
  return typeof v === 'object' && v !== null
    && typeof (v as any).sourceNodeId === 'string'
    && typeof (v as any).targetNodeId === 'string';
}

// ZodError is caught internally; the tool returns a structured VALIDATION_ERROR.
// If invoking the raw schema yourself:
try {
  nodeConnectionSchema.parse(input);
} catch (e) {
  if (e instanceof z.ZodError) { /* e.issues has field-level detail */ }
}

When it happens

Trigger: Missing sourceNodeId or targetNodeId; passing a non-string (object/number) for an ID; passing a string for sourceOutputIndex; passing undefined for a required field.

Common situations: The LLM agent omits a field, passes an object like { id: '...' } instead of the UUID string, or sends indices as strings from a form payload.

Related errors

• VALIDATION_ERROR
• VALIDATION_ERROR
• Tool "${this.name}" requires an input schema
• INVALID_CONNECTION
• SELF_CONNECTION

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/86f56f8ccc93de25. Report an issue: GitHub.