CSV to JSON Converter for CSV and TSV Files of Any Size

Paste CSV or TSV text, drop a file on the input, or load the sample. The JSON updates as you type. The delimiter is detected from the first lines: the tool counts commas, semicolons, tabs and pipes outside quoted text and picks the one that splits the lines into the same number of fields. If detection guesses wrong on an unusual file, choose the delimiter yourself. You can switch between an array of objects, where the header row supplies the keys, and an array of arrays, which keeps the header as the first row.

Cells in quotes may contain delimiters, doubled quotes and line breaks, including Windows CRLF breaks. A leading byte order mark is removed. Spaces around cells and column names are trimmed by default, blank lines are skipped, and empty cells can become null instead of an empty string. If a column name is duplicated or empty it gets a numeric suffix such as name_2 or column_3, and the tool says so.

With type detection on, true and false become booleans, null becomes null, and numbers become JSON numbers. The rules are deliberately cautious. Anything with a leading zero, such as the zip code 00123 or a phone number, stays a string, because turning it into the number 123 destroys information. A number with more than 15 significant digits, for example a 19-digit id, also stays a string, since JSON parsers in JavaScript would round it. Values such as 1,000 or +44 7700 are text too. Switch detection off to keep every cell a string.

This matters because naive converters turn identifiers into numbers. A product code 1E5 or a long order number can silently change. If you need a specific column to be numeric and the tool left it as text, convert it in your code after parsing, where you know the schema.

A quote that opens a cell and never closes would swallow the rest of the file, so the tool refuses that input and points to the line and column where the quote opened. A closing quote followed by more text, as in "x"y, is reported with its line and an explanation: inside a quoted cell a literal quote is written as two quotes. Rows with more or fewer cells than the header are still converted, with missing values set to null and extra values kept under an __extra key, and a warning lists the first line numbers affected.

Inputs above about one megabyte are parsed in a background worker, so typing and scrolling stay smooth. Files up to 50 MB can be loaded; a file over one megabyte is not shown in the editor, only its result. Huge JSON output is truncated in the preview but copy and download always use the full text. For files in the gigabyte range use a streaming command-line tool, because a browser tab has to hold the whole text in memory.