Omikuji Tools Text & Dev

CSV Encoding Converter & Splitter

Fix CSVs that look garbled in Excel, export Shift_JIS, split large CSVs with headers, pick columns or convert to JSON. Your file is never sent to a server.

Features

  • Auto-detects encoding (UTF-8, Shift_JIS, EUC-JP, UTF-16) and delimiter, with a preview to check
  • One click to UTF-8 with BOM (opens cleanly in Excel) or Shift_JIS (CP932), listing characters Shift_JIS cannot hold
  • Split by rows or file size with the header on every file, downloaded as a ZIP
  • Keep only the columns you need, switch comma/tab, convert CSV ⇔ JSON (JSON Lines) and line endings
  • Large CSVs are processed in chunks in a Web Worker, so the page never freezes

Use cases

A downloaded CSV is garbled in Excel

Fix exports from shops, banks or SaaS tools so Excel opens them correctly.

Import into a Shift_JIS-only system

Convert UTF-8 CSVs to Shift_JIS for legacy Japanese systems, and see in advance which characters cannot be converted.

Split a CSV that is too big

Break up files that exceed Excel's ~1,048,576-row limit or an upload size limit, keeping the header on every part.

Feed data to APIs or scripts

Convert CSV to JSON / JSON Lines, or JSON back to CSV.

Privacy

Reading, encoding detection, conversion and splitting all happen inside your browser, on your own device. Your CSV — customer lists, sales data or anything else — is never sent to a server. Files are not stored in the URL or in localStorage and are gone when you close the page.

FAQ

Is my file uploaded?

No. Everything from reading to converting, splitting and zipping happens inside your browser, so it is safe for CSVs that contain personal data.

Should I use UTF-8 with BOM or Shift_JIS?

To open the file in Excel, use UTF-8 with BOM — it keeps every character, including emoji. Use Shift_JIS only when the receiving system explicitly requires it.

How large a file can it handle?

It depends on your device's memory, but CSVs of tens of MB up to around 100 MB work fine. The file is read and converted 4 MB at a time, so the page stays responsive (JSON input is read in one go).

Excel drops leading zeros from postcodes and phone numbers

Excel interprets those values as numbers when it opens the file; the zeros are still in the CSV. Use Data → From Text/CSV in Excel and set the column type to Text to keep them.

Is the header added to every split file?

Yes. When "First row is a header" is checked, every part starts with the same header row.

Related tools

Table Converter Mojibake Generator Full-width ⇔ Half-width

Open a CSV

Drag and drop a CSV, TSV or JSON file here

Or click to choose a file. Files of tens of MB are fine.

Choose a file

To turn a pasted table into Markdown/HTML, or to repair garbled text: Table Converter / Mojibake Repair

Why CSVs look garbled in Excel

When you double-click a CSV, Excel assumes it is in your system's legacy encoding unless it starts with a BOM (byte order mark). Most modern services export UTF-8 without a BOM, so accented letters, Japanese text and emoji turn into garbage. Saving the file as UTF-8 with BOM makes Excel open it correctly. For legacy Japanese systems that only accept Shift_JIS, save as Shift_JIS (CP932).

Privacy

Reading, encoding detection, conversion and splitting all happen inside your browser, on your own device. Your CSV — customer lists, sales data or anything else — is never sent to a server. Files are not stored in the URL or in localStorage and are gone when you close the page.