Unsupported format for "${attachment.fileName}" (${attachmen

Error message

Unsupported format for "${attachment.fileName}" (${attachment.mimeType}). Supported: csv, tsv, json

What it means

Thrown by parseStructuredFile when detectFormat returns a falsy value or returns a format that is not a legacy tabular format (csv/tsv/json) — see isLegacyTabularFormat at structured-file-parser.ts:66. parseStructuredFile only handles csv, tsv, and json; xlsx/html/pdf/docx/markdown/text each have dedicated extractors and must not be routed here.

Source

Thrown at packages/@n8n/instance-ai/src/parsers/structured-file-parser.ts:386

	attachmentIndex: number,
	input: ParseFileInput,
): ParseFileOutput {
	// Decode base64
	let decoded: Buffer;
	try {
		decoded = Buffer.from(attachment.data, 'base64');
	} catch {
		throw new Error('Failed to decode base64 attachment data');
	}

	if (decoded.length > MAX_DECODED_SIZE_BYTES) {
		throw new Error(formatSizeLimitMessage(decoded.length));
	}

	const content = decoded.toString('utf-8');
	const format = detectFormat(attachment.fileName, attachment.mimeType, input.format);
	if (!format || !isLegacyTabularFormat(format)) {
		throw new Error(
			`Unsupported format for "${attachment.fileName}" (${attachment.mimeType}). Supported: csv, tsv, json`,
		);
	}

	const hasHeader = input.hasHeader ?? true;
	const startRow = input.startRow ?? 0;
	const maxRows = Math.min(input.maxRows ?? DEFAULT_MAX_ROWS, MAX_ROWS_PER_CALL);
	const warnings: string[] = [];

	let columns: ColumnMeta[];
	let paginatedRows: Array<Record<string, CellValue>>;
	let totalRows: number;

	if (format === 'json') {
		const { rawHeaders, allRows } = parseJson(content);

		if (rawHeaders.length > MAX_COLUMNS) {
			throw new Error(`Too many columns: ${rawHeaders.length} (max ${MAX_COLUMNS})`);

View on GitHub (pinned to 5ac6606e81)

Solutions

Route xlsx to extractXlsxAsRows and html/pdf/docx to their dedicated parsers instead of parseStructuredFile.
Set a correct mimeType on AttachmentInfo (e.g. text/csv, application/json).
Rename the file to a recognized extension (.csv/.tsv/.json) so detectFormat can infer it.
Pass input.format explicitly as 'csv' | 'tsv' | 'json' when the filename is ambiguous.

Example fix

// before: parseStructuredFile({ fileName: 'data.xlsx', mimeType: 'application/vnd...sheet', data }, 0, { format: 'xlsx' })
// after:  await extractXlsxAsRows({ fileName: 'data.xlsx', mimeType: 'application/vnd...sheet', data }, 0, input)

Defensive patterns

Strategy: validation

Validate before calling

const SUPPORTED = new Set(['csv','tsv','json']);
function routeAttachment(mimeType: string, fileName: string) {
  const ext = fileName.split('.').pop()?.toLowerCase();
  if (mimeType === 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet' || ext === 'xlsx') return 'xlsx';
  // ... text-like formats
  const fmt = SUPPORTED.has(ext ?? '') ? ext : undefined;
  if (!fmt) throw new Error(`Route to parseStructuredFile only for csv/tsv/json; got ${mimeType}/${fileName}`);
  return fmt;
}

Type guard

function isLegacyTabularFormat(f: unknown): f is 'csv' | 'tsv' | 'json' {
  return f === 'csv' || f === 'tsv' || f === 'json';
}

Try / catch

try { return parseStructuredFile(attachment, idx, input); }
catch (e) {
  if (e instanceof Error && e.message.startsWith('Unsupported format for')) {
    // dispatch to the format-specific extractor (xlsx/html/pdf/docx) instead
  }
  throw e;
}

Prevention

Route by mimeType to the correct extractor before calling parseStructuredFile.
Set explicit input.format when the filename is ambiguous.
Keep MIME_TO_FORMAT and isLegacyTabularFormat in sync when adding formats.

When it happens

Trigger: Calling parseStructuredFile with a format hint of 'xlsx', 'html', 'pdf', 'docx', 'text', or 'markdown'; or attaching a file whose name has no recognized extension and whose mimeType is not in MIME_TO_FORMAT. Also when input.format is set to an unsupported value explicitly.

Common situations: A caller routes an .xlsx through parseStructuredFile instead of extractXlsxAsRows; a fileName like 'data.dat' with an arbitrary mimeType; a format string typo; a new format added to SupportedFormat but not to isLegacyTabularFormat.

Related errors

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/38b6f0858507542f. Report an issue: GitHub.