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JSON Unflattener

Rebuild nested JSON from flat dotted or bracketed keys, turning numeric segments into arrays.

Rebuild nested JSON

Rebuilt: —
Keys are split on dots and brackets, numeric segments create arrays, and query strings can be pasted directly.

How to use the JSON Unflattener

  1. Paste flat keys in dot or bracket form, or a query string.
  2. Tick or untick coercion to control number and boolean handling.
  3. Press Rebuild to get the nested JSON document.

Features

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Frequently Asked Questions

Common questions about the free online json unflattener.

Paste flat keys such as user.address.city with values and press Rebuild to get the nested structure back.
Dot notation, bracket notation and mixed forms like user.address[0].city are all split into path segments.
Any path segment that is a whole number becomes an array index, so roles[0] and roles[1] produce a real array.
Yes. If the input is not JSON, it is read as ampersand separated key value pairs, with plus signs treated as spaces.
With coercion on, values that look like numbers, booleans or null are converted to those JSON types instead of staying strings.
The tool waits quietly until there is something to rebuild, and empty keys are skipped rather than creating odd nesting.
No. Every key is parsed and rebuilt locally in your browser, so nothing you paste is transmitted.
Yes. There is no fixed depth limit, so nested paths of any practical length rebuild into nested objects and arrays.
Yes. The unflattener is free to use with no account, no limits and no tracking.

Last updated: October 10, 2026