CSV Validator and Error Finder (Online) – Validate and Clean CSV Files

CSV Validator

Paste a CSV or drop a file to check it for problems before you import it. The validator finds broken quotes and rows with the wrong number of fields, then looks deeper: duplicate rows, blank or repeated column names, values that don't match the rest of their column, mixed date formats, encoding problems, and values Excel would change. Click any issue to jump to that line, then download a fixed copy.

How to use it

1. Paste your CSV on the left, or load a .csv, .tsv, or .txt file. The delimiter is detected automatically.
2. Read the Issues list. Errors are shown first, then warnings. Click a line number to jump to it in the input.
3. Check Columns to see each column's detected type and how many values are filled in, or Preview to see the data as a table with problem cells highlighted.
4. Click Download fixed CSV for a cleaned-up copy, or Report for a list of every issue.

What it checks

Errors break the structure of the file, and most tools will reject it or read it wrong:

• Rows with too few or too many fields compared to the header
• Quotes that are never closed
• Quotes inside a value that isn't wrapped in quotes, and text after a closing quote

Warnings don't break the file, but they often cause trouble during an import:

• Blank, duplicate, or space-padded column names
• Empty rows and exact duplicate rows
• Repeated values in ID columns
• Values that don't fit their column, like n/a in a number column or ben@example in an email column
• Dates that don't exist, like February 30, and columns that mix date formats
• Mixed line endings, files that aren't UTF-8, and garbled characters

Excel checks

Excel changes some values when it opens a CSV. With Excel checks turned on, the validator flags:

To keep values like these, import the file with Excel's Data > From Text/CSV and set those columns to Text.

Fixing a CSV

Open More options to choose what the fixed CSV changes. It can trim extra spaces, remove empty and duplicate rows, pad short rows with empty fields, drop the extra empty field that a trailing delimiter adds, switch the delimiter, and use Windows (CRLF) or Mac and Linux (LF) line endings. Values are quoted correctly, and the file is saved as UTF-8. If you'll open it in Excel, turn on Add BOM for Excel so accented letters and symbols display correctly.

Some problems need a person to fix them, like an unclosed quote or a value with a comma that wasn't quoted. Use the line numbers in the Issues list to find and fix those in the input.

What a valid CSV looks like

The CSV format is defined by RFC 4180. Each line is a row, and fields are separated by a delimiter, usually a comma. A field that contains the delimiter, a quote, or a line break must be wrapped in double quotes, and a quote inside a quoted field is written twice:

id,name,note
1,"Chen, Wei","Said ""hello"" twice"
2,Ana Lopez,

Every row should have the same number of fields as the header. In the example above, the last row's note is empty, but the trailing comma keeps the field count at three.

Frequently asked questions

Does it work with semicolon or tab-separated files?

Yes. The delimiter is detected automatically, and you can also choose comma, semicolon, tab, or pipe yourself. Files that start with Excel's sep= line are handled too.

Why are line endings and the BOM only checked for files?

When you paste text, your browser converts every line ending to the same style, so the original line endings can't be seen. Loading the file lets the validator check its exact bytes.

How large a file can it check?

Files up to 50 MB. The whole file is checked even when only part of it is shown in the input box.

Is my data uploaded?

No. The CSV is checked entirely in your browser, so customer lists and other private data never leave your device.