FlowiseAI/Flowise · error · Error

Unable to resolve fields from header.

Error message

Unable to resolve fields from header.

What it means

CsvLoader calls Papa.parse with header:true and reads fields from meta. If a column selector was requested but fields came back empty, the header could not be resolved. fields is empty when the input is blank, contains only a delimiter row, has no recognizable header, or uses a wrong separator that makes Papa treat everything as one column with an empty name.

Source

Thrown at packages/components/nodes/documentloaders/Csv/CsvLoader.ts:55

     * the `column` option is not specified, it converts each row of the CSV
     * data into key/value pairs and joins them with newline characters.
     * @param raw The raw CSV data to be parsed.
     * @returns An array of strings representing the pageContent of each document.
     */
    async parse(raw: string): Promise<string[]> {
        const { column, separator } = this.options

        const {
            data: parsed,
            meta: { fields = [] }
        } = Papa.parse<{ [K: string]: string }>(raw.trim(), {
            delimiter: separator,
            header: true
        })

        if (column !== undefined) {
            if (!fields.length) {
                throw new Error(`Unable to resolve fields from header.`)
            }

            let searchIdx = column

            if (typeof column == 'number') {
                searchIdx = fields[column]
            }

            if (!fields.includes(searchIdx as string)) {
                throw new Error(`Column ${column} not found in CSV file.`)
            }

            // Note TextLoader will raise an exception if the value is null.
            return parsed.map((row) => row[searchIdx])
        }

        return parsed.map((row) => fields.map((key) => `${key.trim() || '_0'}: ${row[key]?.trim()}`).join('\n'))
    }

View on GitHub (pinned to abe4a8601a)

Solutions

1. Open the file in a text editor and confirm it has a real header row.
2. Verify the separator option matches the file (',', ';', '\t', '|').
3. Strip any BOM or leading blank lines from the source before parsing.
4. If loading from a Blob, ensure the upstream actually produced CSV text.

Example fix

// before
const { data: parsed, meta: { fields = [] } } = Papa.parse(raw.trim(), {
  delimiter: separator, header: true
})
if (column !== undefined && !fields.length) {
  throw new Error(`Unable to resolve fields from header.`)
}
// after - include a preview and try auto-detecting delimiter
const { data: parsed, meta: { fields = [], delimiter: usedDelimiter } } =
  Papa.parse(raw.trim(), { header: true })
if (column !== undefined && !fields.length) {
  throw new Error(`Unable to resolve fields from header (detected delimiter '${usedDelimiter}', preview: ${raw.slice(0, 120)})`)
}

import Papa from 'papaparse'

function assertCsvHasHeader(raw: string, separator?: string): string[] {
  const { meta: { fields = [] } } = Papa.parse(raw.trim(), { delimiter: separator, header: true, preview: 1 })
  if (!fields.length) throw new Error('CSV has no parseable header row - check content and separator')
  return fields
}
// const fields = assertCsvHasHeader(raw, separator) before passing column

function csvHasFields(raw: string, separator?: string): boolean {
  const { meta: { fields = [] } } = Papa.parse(raw.trim(), { delimiter: separator, header: true, preview: 1 })
  return fields.length > 0
}

When it happens

Trigger: Empty file passed to the loader; file is binary/garbage so Papa yields no rows; separator option is wrong (e.g., ';' set but file is comma-delimited) collapsing everything into one unnamed field; file starts with a blank line so header detection fails.

Common situations: Upstream TextLoader received a non-CSV blob; user uploaded an .xlsx renamed to .csv; CSV uses CRLF and a stray quote confuses the parser.

Related errors

• Column ${column} not found in CSV file.
• Invalid JSON in the Chat NVIDIA NIM's baseOptions: ${excepti
• Invalid JSON in the OpenAIEmbedding's BaseOptions:
• Invalid JSON in the ChatOpenAI's BaseOptions:
• Invalid JSON in the OpenAI's BaseOptions:

AI-assisted analysis of FlowiseAI/Flowise@abe4a8601a (2026-08-12). Data as JSON: /api/errors/f9af7cda278092d9. Report an issue: GitHub.