CSV Checker & Converter

How to use

1. Drop in a CSV/TSV file, or paste CSV, TSV or JSON text directly.
2. Click "Analyze & check" to see row and column counts, the detected delimiter, encoding, line-break style and whether a BOM is present.
3. Review warnings about empty rows, ragged column counts, duplicate or blank headers, leading zeros and cells that spreadsheet apps may treat as formulas.
4. Pick an output format (CSV / TSV / JSON) and encoding (UTF-8 / UTF-8 with BOM / Shift_JIS), then copy or download the result.

Choosing an encoding: UTF-8, UTF-8 BOM or Shift_JIS

• UTF-8 is the right default for web services, APIs and data exchanged between programs.
• UTF-8 with BOM helps spreadsheet apps such as Excel recognize UTF-8 when you open the file with a double-click. The BOM is an invisible three-byte marker at the start of the file.
• Shift_JIS (CP932) is still required by some legacy business systems and older Japanese Excel workflows. If your data contains characters that Shift_JIS cannot represent, the tool stops with an explicit error instead of silently replacing them.

Structure checks and spreadsheet risks

Beyond encoding, the checker flags problems that commonly break CSV imports: empty rows, rows whose column count differs from the first row, and duplicate or blank header names. It also warns about values with leading zeros (such as postal codes) that spreadsheet apps may silently turn into numbers, and cells starting with =, +, - or @ that can be executed as formulas (CSV injection). The tool never rewrites your values — it only reports what it finds.

JSON conversion scope and limits

Converting CSV to JSON yields an array of flat objects using the header row as keys. No type inference is applied: numbers, booleans and identifiers all stay strings, so leading zeros survive the round trip. Converting JSON to CSV accepts an array of flat objects only; nested structures are rejected with a clear message.

Privacy

Everything — reading, encoding detection, checks, conversion and download — runs locally in your browser. Customer lists and internal data never leave your device. Files up to 10MB are supported; the preview shows the first 100 rows and 50 columns.

FAQ