n8n-io/n8n · error · Error

No prompt found in inputs - expected "prompt" string or "mes

Error message

No prompt found in inputs - expected "prompt" string or "messages" array

What it means

`extractPrompt` reads a single prompt from a LangSmith dataset example's `inputs`. It accepts either a `prompt` string or a non-empty `messages` array (in which case it takes `messages[0]`). If neither shape is present, the example is unusable and the harness aborts. This protects downstream agents from being invoked with an undefined prompt.

Source

Thrown at packages/@n8n/ai-workflow-builder.ee/evaluations/harness/runner.ts:1002

	[key: string]: unknown;
}

/**
 * Extract prompt from dataset input.
 * Supports both direct prompt and messages array format.
 */
function extractPrompt(inputs: LangsmithDatasetInput): string {
	// Direct prompt string
	if (inputs.prompt && typeof inputs.prompt === 'string') {
		return inputs.prompt;
	}

	// Messages array format
	if (inputs.messages && Array.isArray(inputs.messages) && inputs.messages.length > 0) {
		return extractMessageContent(inputs.messages[0]);
	}

	throw new Error('No prompt found in inputs - expected "prompt" string or "messages" array');
}

/**
 * Pre-process LangSmith examples to extract conversation history from outputs
 * and inject it into inputs for the target function.
 *
 * The dataset format has:
 * - inputs.messages[0]: The latest user turn
 * - outputs.messages: The FULL conversation (all prior turns + latest + AI response)
 *
 * We find the latest turn in outputs and extract everything before it as historical.
 */
function enrichExamplesWithHistory(examples: Example[]): Example[] {
	return examples.map((example) => {
		const outputMessages = (example.outputs as Record<string, unknown> | undefined)?.messages;
		if (!Array.isArray(outputMessages) || outputMessages.length <= 1) {
			return example; // No history to extract
		}

View on GitHub (pinned to 5ac6606e81)

Solutions

1. Open the dataset in the LangSmith UI and confirm each example's `inputs` has either a `prompt` string or a non-empty `messages` array.
2. If your schema uses a different field, either rename it to `prompt` in the dataset or extend `extractPrompt` to read your field.
3. Filter out malformed examples before running, or fix them in place.

Example fix

// before
// example.inputs = { workflowJSON: {...} }  (no prompt/messages)
// after
// example.inputs = { prompt: "build a slack notifier", workflowJSON: {...} }

function hasUsablePrompt(inputs: unknown): boolean {
  if (!inputs || typeof inputs !== 'object') return false;
  const r = inputs as Record<string, unknown>;
  if (typeof r.prompt === 'string' && r.prompt.length > 0) return true;
  return Array.isArray(r.messages) && r.messages.length > 0;
}
// filter the dataset up front
const usable = examples.filter((e) => hasUsablePrompt(e.inputs));
if (usable.length === 0) throw new Error('no dataset examples have a prompt or messages array');

function isPromptableInput(inputs: unknown): inputs is { prompt: string } | { messages: unknown[] } {
  if (!inputs || typeof inputs !== 'object') return false;
  const r = inputs as Record<string, unknown>;
  if (typeof r.prompt === 'string' && r.prompt.length > 0) return true;
  return Array.isArray(r.messages) && r.messages.length > 0;
}

When it happens

Trigger: A dataset example whose `inputs` has neither a `prompt` field nor a `messages` array — e.g. it only carries `workflowJSON`, custom metadata, or a `messages` array that is empty. Also triggered by malformed examples uploaded with the wrong field names.

Common situations: Dataset schema drift (field renamed from `prompt` to `user_prompt`); examples created by a different tool that uses `input`/`query`; an example whose `messages` array was stripped during export; copy-pasting an example and dropping the prompt field.

Related errors

• LangSmith mode requires dataset to be a dataset name string
• No message provided
• Message content must be a string or contain text content
• Tool "${this.name}" requires an input schema
• LangSmith mode requires `--dataset` and does not support `--

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/eadbfc98ec1cceb8. Report an issue: GitHub.