n8n-io/n8n · error · NodeOperationError

The maximum number of files that can be attached to the assi

Error message

The maximum number of files that can be attached to the assistant is 20

What it means

When creating an OpenAI assistant, if more than 20 file IDs are provided for code_interpreter tool resources, the code throws a NodeOperationError before making the API call. This mirrors OpenAI's hard limit of 20 files attached to an assistant's code interpreter. The check is client-side pre-validation.

Source

Thrown at packages/@n8n/nodes-langchain/nodes/vendors/OpenAi/v1/actions/assistant/create.operation.ts:229

			if (has_more) {
				after = response.last_id;
			} else {
				break;
			}
		} while (has_more);

		if (assistants.includes(name)) {
			throw new NodeOperationError(
				this.getNode(),
				`An assistant with the same name '${name}' already exists`,
				{ itemIndex: i },
			);
		}
	}

	if (file_ids.length > 20) {
		throw new NodeOperationError(
			this.getNode(),
			'The maximum number of files that can be attached to the assistant is 20',
			{ itemIndex: i },
		);
	}

	const body: IDataObject = {
		model,
		name,
		description: assistantDescription,
		instructions,
	};

	const tools = [];

	if (codeInterpreter) {
		tools.push({
			type: 'code_interpreter',

View on GitHub (pinned to 5ac6606e81)

Solutions

1. Reduce the file_ids list to 20 or fewer entries
2. Consolidate documents into fewer files before uploading
3. Use OpenAI's file_search (vector store) tool instead, which supports more files via vector stores

Example fix

// before — file_ids: ['file1', 'file2', ..., 'file25']
// after  — file_ids: ['file1', ..., 'file20'] // trim to <= 20

const MAX_FILES = 20;
const fileIds = getFileIds(file_ids);
if (fileIds.length > MAX_FILES) {
  throw new UserError(`Cannot attach ${fileIds.length} files. Maximum is ${MAX_FILES}.`);
}

When it happens

Trigger: The file_ids array (or comma-separated string) provided to the Create Assistant operation contains more than 20 file IDs. The count is checked after parsing and before the POST request.

Common situations: Attaching a large document set to an assistant; merging multiple file collections into one assistant; not realizing OpenAI caps assistant files at 20.

Related errors

• The maximum number of files that can be attached to the assi
• An assistant with the same name '${name}' already exists
• ${error.message}
• Invalid file_ids type
• The file content is not in JSONL format

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/c7d20f5ef44129ba. Report an issue: GitHub.