FlatNest

Flatten & unflatten nested JSON

Flatten nested JSON online (or unflatten it back)

Turn deep objects into flat dot.notation keys for spreadsheets, configs, and APIs — or rebuild nested JSON from a flat map. Everything runs in your browser; your data never leaves this device.

No signup No server upload Dot or custom separator Free under 80k chars
Input JSON 0 chars
Output

What does “flatten nested JSON” mean?

Nested JSON stores values under objects inside objects (for example user.profile.email). Flattening turns that tree into a single-level map of path keys, which is easier to filter in spreadsheets, ship as env-style configs, or feed into ETL pipelines. Unflatten does the reverse: rebuild a nested object from those path keys.

When to use FlatNest

  • Convert API payloads into flat rows for CSV / BI tools
  • Normalize config files that mix nested and flat styles
  • Debug deeply nested responses without scrolling a giant tree
  • Prepare test fixtures with predictable key paths

Privacy

Conversion is 100% client-side JavaScript. We do not upload your JSON, store it, or require an account for the free tier. See the privacy page.