Tablizer

Convert CSV to JSON Lines Online

Paste a CSV table below, edit it if you need to, and get JSON Lines back. The conversion runs in your browser, so nothing is uploaded, there is no size limit and there is no signup.

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The output will appear here once there is a table to convert.

What CSV is

CSV is a text file where each line is a row and commas separate the fields. There is no type system, no formatting and no second sheet. Every value is text until something downstream decides otherwise.

Almost every database, analytics tool and spreadsheet can read and write it, which is why exports default to it.

What JSON Lines is

JSON Lines is one complete JSON object per line, with no enclosing array and no commas between records. The file is not valid JSON as a whole, and that is the point.

Log pipelines, machine learning datasets and anything that appends records or reads them in a stream.

What changes when you convert CSV to JSON Lines

Reading CSV means deciding three things the file does not state: which character separates fields, how quotes work, and what encoding the bytes are in. Tablizer sniffs the delimiter from the first few lines, handles quoted fields containing commas and newlines, and reads the file as UTF-8.

Every row becomes one line. You can append to the file forever without rewriting it, and a reader can process it a line at a time without holding the whole thing in memory.

What carries over from CSV to JSON Lines

CSV records 2 things about a table that JSON Lines has no way to hold.

JSON Lines wants a type for each column, and CSV does not record one, so each column is typed from what its values look like. A column of digits that should stay text - a zip code, a phone number, a leading-zero id - is the usual thing to check afterwards.

A line break inside a cell ends the row in JSON Lines, so line breaks are replaced rather than carried through.

JSON Lines has no header row. The column names are repeated as keys on every record instead, which is why the result is bigger on disk than the table it came from.

The identifier 007 comes out of the JSON Lines as 007. Reading it as a number would have made it 7, and an id that changes value is worse than one that stays text.

The role "Analyst, data" survives with its comma, in one cell rather than split across two. That is the first thing to check in any converted table, and the usual place a JSON Lines file goes wrong.

The quotes around Jonah "Jo" Pryce are escaped with a backslash in the JSON Lines.

A worked example

Three rows of staff data, with an identifier that has a leading zero, a value containing a comma, a value containing quotes and one blank cell. Those are the four places formats disagree, so they are the four places to look.

CSV in
id,name,role,started,hours
007,Halima Yusuf,"Analyst, data",2024-03-15,38.5
012,"Jonah ""Jo"" Pryce",Engineer,2025-11-02,
104,Wei Chen,Manager,2023-06-30,40
JSON Lines out
{"id":"007","name":"Halima Yusuf","role":"Analyst, data","started":"2024-03-15","hours":"38.5"}
{"id":"012","name":"Jonah \"Jo\" Pryce","role":"Engineer","started":"2025-11-02","hours":""}
{"id":"104","name":"Wei Chen","role":"Manager","started":"2023-06-30","hours":"40"}

Questions

How do I convert CSV to JSON Lines?

Paste your CSV into the box above or drop the file onto it. Check the table in the grid, then copy or download the JSON Lines from the output panel. It takes one step and the data never leaves your browser.

Why does my CSV open with all the data in one column?

The file uses a delimiter your spreadsheet did not expect. Exports from European locales often use semicolons because the comma is the decimal separator there. Change the delimiter in the export options and the columns split correctly.

What is the difference between JSON and JSON Lines?

JSON wraps records in an array, so a reader must load the whole document before it can use any of it, and appending means rewriting the file. JSON Lines has no wrapper, so records can be streamed and appended one at a time. Use JSON for a payload, JSON Lines for a log.

One of my cells has a line break in it - what happens?

A line break would end the row in JSON Lines, so it is replaced instead of carried through. The rest of the cell stays where it belongs.

Is there a limit on file size?

No. The work happens on your own machine, so the limit is your machine's memory rather than an upload cap. A file with tens of thousands of rows converts in a second or two.

Is my data uploaded anywhere?

No. The parsing and generating are done by JavaScript running on this page. You can watch the network tab while you convert and see that nothing is sent.

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