Nested JSON ⇄ Excel (Flatten)
Flatten nested JSON objects into an Excel spreadsheet, or rebuild nested JSON from a flattened workbook. Supports files up to 200MB (Excel output is limited to 1,048,576 rows per the .xlsx format spec — convert to CSV or JSON instead for unlimited rows) — everything runs entirely in your browser.
Or convert a .json file directly — supports files up to 200MB
Drag & drop a file here, or click to browse
Processed in the background, so the page stays responsive even for huge files
How to use this tool
Switch to JSON → Flat Excel, paste nested JSON — objects inside objects, arrays of values — and click Convert & Download .xlsx to get a spreadsheet where every field becomes its own column, named with dot notation like address.city. Switch to Excel → Nested JSON and drop in a workbook that uses the same dotted-header convention; the tool reads the first sheet and rebuilds the original nested structure automatically. Files up to 200MB are supported — large uploads are processed in a background Web Worker so the page never freezes, and everything happens locally in your browser.
Frequently Asked Questions
Is there a file size limit?
Yes — files up to 200MB are supported. Conversion runs in a background Web Worker, so even large files process smoothly without freezing your browser tab. Files over 200MB are rejected immediately with a clear message. Excel output specifically is capped at 1,048,576 rows (a limit of the .xlsx format itself, not something we control) — convert to CSV or JSON instead if you need more rows than that.
Is my data uploaded anywhere?
No. Every conversion happens locally in your browser, including for large files — nothing is ever sent to a server.
What does Excel → Nested JSON convert?
It reads the first sheet of the uploaded workbook and rebuilds nested objects and arrays from dotted column headers like address.city or hobbies.0.
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