Unflatten JSON Online.
Rebuild nested JSON from flat keys using dot notation, bracket notation, slash paths, or underscore keys. Auto-detect delimiters, turn numeric paths into arrays, and copy clean nested JSON instantly.
No signup · No uploads · Auto-detect delimiter
Nested JSON output
// Nested JSON appears here.Unflatten JSON from flat keys
A JSON unflatten tool converts one-level JSON objects
back into nested data. Flat keys such as user.address.city
become real nested objects, while numeric paths such as
users.0.email can rebuild arrays. It is useful when a
spreadsheet export, log pipeline, analytics tool, database column map,
or flattened API response needs to become structured JSON again.
How to unflatten JSON in three steps
- Paste flat JSON with path-like keys into the input.
- Choose delimiter - auto-detect, dot, bracket, slash, or underscore.
- Rebuild nested JSON, then copy or download the result.
Dot notation, bracket notation, slash, and underscore
Different systems flatten keys in different ways. This
unflatten JSON online tool handles dot notation
(user.name), bracket notation (user[name]),
slash paths (user/name), and underscore keys
(user_name). Auto-detect works well for common exports,
while manual delimiter selection gives you control when a dataset has
unusual key names.
Rebuild arrays from numeric keys
Keys like roles.0 and roles.1 can become
arrays instead of objects when numeric-key coercion is enabled. Disable
it when numbers are meaningful object property names. This makes the
tool flexible for API payloads, NoSQL exports, log events, and form
data.
Reverse flatten JSON safely
The conversion runs entirely in your browser, so private data stays on your device. Need the opposite direction? Use JSON Flatten to turn nested JSON into flat path keys, or inspect the rebuilt structure with JSON Viewer. For a deeper walkthrough, read how to unflatten JSON.
FAQ
Unflatten JSON, answered.
How do I unflatten JSON online? +
Paste a flat JSON object into the JSON Unflatten tool, keep Auto detect selected or choose the delimiter, and press Unflatten JSON. The tool rebuilds nested objects and arrays from path-like keys.
Can this rebuild nested JSON from dot notation keys? +
Yes. Dot notation keys such as user.address.city become nested objects like user > address > city. Numeric dot keys such as users.0.name can also become arrays when numeric-key coercion is enabled.
Does it support bracket notation JSON keys? +
Yes. The tool can unflatten bracket notation keys such as user[address][city], plus slash paths like user/address/city and underscore keys like user_address_city.
How does delimiter auto-detect work? +
Auto detect checks the flat keys and chooses bracket, slash, dot, or underscore parsing. If your keys use a mixed or unusual pattern, choose the delimiter manually for the most predictable result.
Can I turn numeric keys into arrays? +
Yes. With Coerce numeric keys to arrays enabled, keys such as roles.0 and roles.1 rebuild into a JSON array. Turn it off if numeric keys should stay as object properties.
Is my flat JSON uploaded? +
No. Unflatten JSON runs entirely in your browser. Your data is never uploaded, stored, logged, or sent to a server.