Prepare tabular data
Turn nested values into path-based columns for exports and quick inspection.
100% local · files never leave your browser
Convert tool
Flatten or Unflatten JSON
Flatten nested JSON into dot paths or rebuild nested JSON from flat keys locally in your browser.
✓ Free to use✓ No signup✓ Runs locally
67 bytes · local only
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Processed entirely in this tab
Your input and result are not sent to JSON Hearth or stored on a server.
When to use it
What Flatten JSON helps you do
Flattening converts nested paths into simple keys, while unflattening reconstructs objects from those paths. It is useful for tables, environment-style data and comparisons.
Compare configurations
Represent deeply nested settings as a flat list of keys and values.
Rebuild nested objects
Convert dot-path keys back into objects when importing flat configuration data.
How it works
Flatten JSON, without the upload.
Add your data
Paste a value, open a local file or begin with the working sample.
Run the tool
The transformation executes in your browser, not on our servers.
Review the result
Check the output, then copy or download it for your next task.
Important limitations
What to check before using the result
Review required
Keys that already contain separator characters can be ambiguous without an agreed escaping convention.
Review required
Arrays and sparse indexes may not map cleanly between every flattening implementation.
Common questions
About Flatten JSON
Does Flatten or Unflatten JSON upload my data?
No. Your input is processed by code running in your browser and is not sent to an application server.
Is Flatten JSON free to use?
Yes. The tool is free, requires no account and can be used directly in the browser.
What is a flattened JSON path?
It is a key such as user.address.city that represents a value nested inside several objects.
Can flattening always be reversed?
It is reversible when the path convention is unambiguous and no original keys collide with generated paths.