What happens to nested objects when converting JSON to CSV?

CSV is flat, so nested objects and arrays are written into their cell as JSON text. Objects with different keys are combined: every key becomes a column and missing values are left empty.

Why did my numbers stay as strings?

Only plain numbers are converted. Leading zeros (like ZIP codes), very long digit strings and values with extra characters stay as text so they aren't changed or rounded. Turn off type detection to keep everything as text.

My CSV opens in Excel with everything in one column. Why?

Excel in many regions expects semicolons. Choose the semicolon delimiter when converting JSON to CSV.

Is there a size limit?

There's no fixed limit, but very large files (tens of megabytes) may make your browser slow, since everything runs on your device.

CSV ↔ JSON Converter

Turn CSV into JSON or JSON into CSV, with proper handling of quotes, commas and headers.

Processed locally

CSV

JSON

Quoted fields, commas and line breaks inside values, and escaped quotes ("") are all handled.

Instructions

How to use it

01Choose CSV → JSON or JSON → CSV.
02Paste your data into the left box. The result updates as you type.
03Adjust the delimiter and header options if needed, and check any warnings about uneven rows.
04Copy the output or download it as a .json or .csv file.

About

What it does

CSV is how spreadsheets and databases export tables; JSON is how web apps and APIs exchange data. Converting between them sounds simple until a value contains a comma, a quote or a line break, which is exactly where quick scripts go wrong.

This converter uses a standards-compliant parser (RFC 4180), so quoted fields, escaped quotes (""), commas and line breaks inside values all come through intact. It also detects whether your file uses commas, semicolons or tabs.

Supported formats

CSV / TSV: Comma, semicolon, tab or pipe separated, with or without a header row.
JSON: An array of objects, an array of arrays, or an object wrapping a single array (like {"items": [...]}).

Settings explained

Delimiter: Auto-detect works for comma, semicolon (common in European Excel exports), tab and pipe separated files.
First row is headers: On: each row becomes an object with named fields. Off: each row becomes an array of values.
Detect numbers & booleans: Turns 42 into a number and true into a boolean. Values like 007 or 20-digit IDs stay as text so nothing is lost; empty cells become null.

Good for

Turning a spreadsheet export into JSON for an API or seed file
Exporting API results to CSV to open in Excel or Google Sheets
Cleaning up CSV files that break other importers
Converting test fixtures between formats

Questions, answered

What happens to nested objects when converting JSON to CSV?: CSV is flat, so nested objects and arrays are written into their cell as JSON text. Objects with different keys are combined: every key becomes a column and missing values are left empty.
Why did my numbers stay as strings?: Only plain numbers are converted. Leading zeros (like ZIP codes), very long digit strings and values with extra characters stay as text so they aren't changed or rounded. Turn off type detection to keep everything as text.
My CSV opens in Excel with everything in one column. Why?: Excel in many regions expects semicolons. Choose the semicolon delimiter when converting JSON to CSV.
Is there a size limit?: There's no fixed limit, but very large files (tens of megabytes) may make your browser slow, since everything runs on your device.

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