Move tabular data between CSV, TSV and JSON. Choose how records map, review the result and download a copy. Your source stays in place.
Default CSV mapping: 001 → "001". Every cell stays a string.
Choose a mapping and source, then convert.
Open one UTF-8 file up to 8 MB. No draft is saved.
Convert to prepare an output.
Know what crosses over.
CSV has cells. JSON has types and structure. Choose the mapping rather than asking the tool to guess.
Will numbers, dates and empty cells change?
CSV cells become JSON strings by default, including 001, true, null, dates and empty strings. Spaces are kept. Object mode uses the first record as exact keys; blank or duplicate keys and inconsistent record widths need correction. Row arrays keep every record, including headers and uneven widths.
What happens to JSON types and nested data?
Use a root array of objects or row arrays. Numbers keep their written spelling. Boolean and null values become the text true, false and null. Nested objects or arrays become JSON text in one cell; they are not flattened. CSV does not retain these JSON types. Objects require matching key sets unless you explicitly allow empty cells for missing fields. Empty root arrays make an empty file; zero-column records cannot be represented faithfully and are rejected.
Is the CSV safe to open in any spreadsheet?
Cells are preserved, not rewritten for a spreadsheet. Formula-like cells receive a warning. CSV quoting does not universally prevent formula execution, and spreadsheet apps may change types, dates or identifiers when importing. Review the result and the destination app's import settings. This tool does not certify a file as safe.
What are the limits?
One UTF-8 file up to 8 MB; 2,000,000 input text units; 8,000,000 output text units; 100,000 records; 1,000 columns; 1,000,000 cells; 128 nested JSON levels and 300,000 JSON nodes. Emoji may use more than one text unit. Header records count toward limits. The preview shows at most 100,000 text units; copy and download include the full result. Cancel stops the current task and keeps the source.
Are my source or files saved?
This tool does not upload or save a draft. Import and processing stay on this device. Copy or download before leaving. UTF-8 byte-order marks are skipped. Imported line endings are tracked separately from the browser editor; if an edit cannot be tracked reliably, a notice explains the limitation. Re-open the original file to restore exact line endings.