How do you flatten nested JSON?

Objects become dotted keys (user.name). Arrays become index suffixes (tags.0). Switch to “stringify” if you want a nested value in one cell.

One JSON object per line, no wrapping array. If JSON.parse fails, we try line-by-line.

Excel on Windows often misreads UTF-8 CSV without a BOM. Google Sheets does not need it. The checkbox is on by default for Excel.

Is my API response uploaded?

No. Conversion is entirely in the browser.

Can I go the other way?

Yes — use the CSV to JSON converter. Same delimiter options.

Runs in your browser · Last updated 4 September 2026

JSON to CSV Converter

Flatten JSON or NDJSON into Excel-ready CSV in your browser. Nested keys, UTF-8 BOM, no upload.

Nested keysUTF-8 BOM for ExcelDelimiter

JSON or NDJSON

CSV

id,user.name,user.city,tags.0,tags.1
1,Ada,London,math,engine
2,Grace,New York,navy,

How to use this tool

Paste an array of objects, a single object, NDJSON, or { data: [...] }.
Choose flatten vs stringify and a delimiter.
Leave BOM on if you will double-click the file in Excel.
Copy the CSV.

Worked example

The sample has two users with nested user.city and a tags array. Flatten mode yields columns id, user.name, user.city, tags.0, tags.1. Grace has one tag, so tags.1 is empty. That is expected: CSV is rectangular.

Frequently asked questions

How do you flatten nested JSON?: Objects become dotted keys (user.name). Arrays become index suffixes (tags.0). Switch to “stringify” if you want a nested value in one cell.
What is NDJSON?: One JSON object per line, no wrapping array. If JSON.parse fails, we try line-by-line.
Why the UTF-8 BOM?: Excel on Windows often misreads UTF-8 CSV without a BOM. Google Sheets does not need it. The checkbox is on by default for Excel.
Is my API response uploaded?: No. Conversion is entirely in the browser.
Can I go the other way?: Yes — use the CSV to JSON converter. Same delimiter options.