xlsx · csv · json both directions

When to use it

A vendor sent an Excel sheet that needs to land in code (JSON, a database import). Or you have JSON / CSV data that an internal user wants as Excel.

Supported formats

• Reading — xlsx, xls, xlsm, ods, csv. One file at a time.
• Writing — xlsx, single sheet. You name the sheet.

Cell types

• Numbers — preserved as-is. Integers, decimals, scientific notation.
• Dates — exported to JSON as ISO 8601 strings (e.g. 2026-04-29T00:00:00.000Z), not Excel serial numbers — so the round trip is lossless.
• Blank cells — null in JSON, empty field in CSV.
• Formulas — only the last computed value is read. The formula itself is dropped.

First-row-as-header

A toggle on the JSON output.

• On (default) — row 1 becomes keys. { "id": ..., "name": ... }.
• Off — keys default to col_1, col_2, ... For raw data dumps with no header row.

Large files

Up to 50MB is accepted. Anything over 10MB may briefly hang the tab during parse; over 100MB is not recommended on a laptop (the browser may show an unresponsive prompt).

Privacy

A vendor sales sheet, an internal HR table, a client roster — none of it leaves the page. The file lives briefly as an ArrayBuffer in memory and disappears when the tab closes.

Not the right tool when

• You need formulas to survive — only values come through. If the formulas, macros, charts, or conditional formatting must remain alive, use Excel itself.
• You want every sheet exported at once — one sheet per export. For multi-sheet files, switch the tab and download each one.
• You need a visual conversion (xlsx → pdf) — table styling, paper layout, headers/footers belong to Excel's PDF export.