CSV validator
Check a CSV before you import it. The validator lists every structural problem with its line number, from rows with the wrong number of fields to unbalanced quotes, and can suggest a repaired file.
Loading the tool…How to use it
- Paste or drop the CSV.
- Read the report: errors break imports, warnings are worth a look.
- Jump to a problem line, fix it, or use “Suggest a fix with AI” and review the diff.
Private by design
The conversion runs as JavaScript in this tab. Your data is not uploaded, logged or stored, unless you choose the optional AI fix. There is no account and no file-size paywall.
Why some CSV fields get quotes
CSV looks trivial until a value contains the separator itself. Type a value, or pick one, and watch how a correct writer (RFC 4180) has to encode it, and how a naive “join with commas” breaks the row.
- Contains a comma → must be wrapped in quotes
- Contains a double quote → wrap in quotes and write each " as ""
- Contains a line break → must be wrapped in quotes
- Starts or ends with a space → quoting is optional but keeps the space safe
1,Ada,"Arlington, VA",UK
Parsed back: 4 fields ✓ — city = "Arlington, VA"
1,Ada,Arlington, VA,UK
Broken: parsed as 5 fields, so every column after the city shifts right.
What it checks
Errors: rows with more or fewer fields than the header, a quote that opens but never closes, a quote character in the middle of an unquoted field, and blank or duplicated header names. Warnings: mixed line endings (CRLF and LF), a byte-order mark, trailing whitespace in headers, completely empty rows, the Unicode replacement character (a sign the file was saved in the wrong encoding), and cells starting with = + - @ that spreadsheets may run as formulas.
The standard behind it
RFC 4180 (2005) is the closest thing CSV has to a specification: records are separated by line breaks, fields by commas, and any field containing a comma, a double quote or a line break must be wrapped in double quotes, with inner quotes doubled. Many real-world files deviate, which is exactly what this tool reports.
Questions
Is my file uploaded anywhere?
No. The file is read by JavaScript in this tab and never leaves your device. You can load the page, switch off Wi-Fi and it keeps working.
Does the AI fix upload my file?
Only if you click “Suggest a fix with AI”. Then the first 8,000 characters are sent to an AI model to propose corrections, and nothing is stored. Validation itself never leaves your browser.
Can it validate against a schema?
It checks structure, not business rules. For column types, the report shows each column’s inferred type and how many values do not fit it.
Does it handle semicolon CSVs?
Yes. The delimiter is detected, or you can set it.