JSON Flattener

A JSON flattener converts a nested JSON object into a single-level object whose keys are the full path to each value, so {"user":{"city":"Austin"}} becomes {"user.city":"Austin"}. Arrays flatten the same way, using the index as a path segment: {"roles":["admin","editor"]} becomes {"roles.0":"admin","roles.1":"editor"}. The result is a flat map of path to leaf value with no remaining nesting.

Flattening is how you get deeply nested API responses and config files into formats that only understand flat key-value pairs. Spreadsheet columns, environment variables, dotted i18n message keys, feature-flag stores, and many logging and analytics pipelines all expect one level of keys, and a dotted path such as user.address.city is the standard way to carry the original structure through them. The reverse operation, unflatten, rebuilds the nested object and its arrays from those dotted keys, so the transform is a lossless round trip in both directions.

This tool runs entirely in your browser. It parses the JSON, walks it to leaf values, and serialises the flat or nested result without sending anything to a server. Nothing is uploaded, logged, or stored, which keeps payloads with tokens, IDs, or personal data on your machine, and the tool keeps working offline once the page has loaded.

Flattening trades structure for a shape that spreadsheets, form encoders and environment variables can carry, and the round trip is lossless in both directions provided one thing holds: your keys must not already contain the delimiter. A key named "user.name" flattened with a dot is indistinguishable from a nested object, and unflattening will turn it into one. Change the delimiter to something the data does not use when that is a risk. Array indices become numeric path segments, so items.0.id addresses the first element, and an unflattener has to decide whether a numeric key means an array or an object with numeric keys. Empty objects and empty arrays are preserved explicitly rather than dropped, since losing them would change the meaning of a config file.