About JSON Flatten / Unflatten

Flatten nested JSON to dot-notation or unflatten back. Part of the DevTools Surf developer suite. Browse more tools in the JSON collection.

Use Cases

• Explore deeply nested API responses by listing all paths
• Convert nested configs to flat environment variable format
• Generate documentation of all fields in a JSON schema
• Prepare hierarchical data for flat-file or CSV export

Tips

• Flatten deep JSON to dot-notation for quick scanning
• Unflatten dot-notation paths back to nested structure
• Use the flattened output as a key list for documentation

Fun Facts

• Dot-notation for nested objects originated in JavaScript property access syntax defined in the ECMAScript 1 specification in 1997.
• MongoDB uses dot-notation in queries to access nested document fields, making flattened keys directly usable as Mongo query paths.
• Flattening a 10-level deep JSON object can reveal hundreds of leaf paths, making it invaluable for understanding complex API responses.

FAQ

What does flattening do to nested JSON?

Every leaf value becomes a key in a single flat object, with the path encoded as dot-separated keys (`user.address.city`). Arrays use bracket indexes (`items[0].id`).

Why would I flatten JSON?

CSV export, feature engineering for ML, comparing nested configs as a list, and loading into column-stores that don't handle nested types natively.

Can I reverse the flatten?

Yes — the same tool unflattens. Paste dot-notation keys and values and it rebuilds the nested object/array structure.

What about keys that contain dots?

By default dots in original keys are preserved in the flattened output and the tool uses a configurable separator ('.', '/', '__') so you can avoid collisions.