Validate CSV structure

About this tool

CSV structure validator lints the raw text of a CSV and reports every structural fault with a 1-based line number and a severity — without changing your data. Unlike most CSV parsers, which quietly "repair" a broken file, this tool scans the text directly, so it can show you exactly what an importer will choke on.

It reports errors (the file breaks RFC 4180 parsing):

• ragged_row — a row's field count differs from the header/first row.
• unclosed_quote — a quoted field is opened but never closed (reported at the line where the quote opens).
• stray_quote — a bare quote inside an unquoted field, or text after a closing quote.

And warnings (parseable, but usually unintended):

• blank_row — an empty or whitespace-only line.
• empty_row — a row whose every field is empty (e.g. ,,).
• whitespace — leading/trailing spaces around fields or quotes.
• empty_header / duplicate_header — blank or repeated header names.
• mixed_line_endings — the file mixes CRLF, LF, or CR.

The file is valid when it has zero errors — warnings alone don't fail it.

Worked example

Input:

name,email,city
Ada,[email protected],Paris,extra
Bo,bo"x,Rome
Cy,"[email protected]

Report:

INVALID CSV — 3 error(s), 0 warning(s).
Delimiter: comma (auto-detected) · Quote: double · Expected 3 field(s) per row · 3 data row(s)
Line 2 [error] ragged_row — expected 3 field(s), found 4
Line 3 [error] stray_quote — unquoted field 2 contains a bare quote character — wrap the field in quotes and double any embedded quote
Line 4 [error] unclosed_quote — quoted field 2 is opened here but never closed

Limits and edge cases

• The expected column count comes from the first row (the header when "first row is a header" is on). Quoted fields may legally contain the delimiter and even newlines — they are parsed, not flagged.
• A row swallowed by an unclosed quote skips the field-count check (its count would be meaningless), so one mistake doesn't cascade into dozens of errors.
• A leading byte-order mark (BOM) is stripped before scanning; character encoding itself isn't checked — the input is already text when it arrives.
• Browser text areas normalize CRLF to LF when you paste, so the mixed_line_endings check is most useful from the CLI or chat, where the file's original line endings survive.
• max_issues (1–1000, default 50) caps the listed issues; the error and warning totals always cover the whole file and the report says when the list is truncated.
• This tool reports only — it never rewrites your CSV. To fix findings, companion tools such as csv-cleaner (trim whitespace, drop empty rows, normalize delimiters/line endings) and csv-find-incomplete-rows (blank required cells) pick up from this report.

Privacy

Everything runs in your browser via WebAssembly — your CSV is never uploaded. The same validator is available from the CLI and in chat, which return the full report as structured JSON (verdict, dialect, counts, and every issue with line, severity, code, and message).

Common uses

• Find the exact line that makes a spreadsheet import or ETL job fail.
• Check an export for unescaped quotes or delimiters before shipping it.
• Confirm a hand-edited CSV still has a consistent column count everywhere.
• Spot header problems (duplicate or blank names) before loading into a database.

FAQ