JSON Flatten & Unflatten

Flatten nested JSON to dot/bracket keys online — or unflatten flat keys back to nested objects and arrays. Custom separators, lossless round-trip, no upload.

Separator

Nested JSON input

{
  "user": {
    "name": "Ada",
    "address": { "city": "London", "zip": "SW1Y" },
    "roles": ["admin", "editor"]
  },
  "active": true
}

Flattened JSON

{
  "user.name": "Ada",
  "user.address.city": "London",
  "user.address.zip": "SW1Y",
  "user.roles[0]": "admin",
  "user.roles[1]": "editor",
  "active": true
}

About JSON Flatten & Unflatten

Flatten turns nested objects and arrays into a single-level map like "a.b[0].c": value — choose the key separator and whether arrays become a[0], a.0 or stay as leaf values. Empty objects and arrays are preserved as leaves.

Unflatten reverses it: numeric key segments become arrays automatically (a[0], a.0 and mixed forms all work), conflicting paths are reported, and a flatten→unflatten round-trip restores the original document exactly. Everything runs locally in your browser.