Flatten JSON Array

Somewhere between the pipeline that groups the data and the consumer that needs a plain list, someone has to deal with the array of arrays. It looks like this: [[1,2],[3,[4,5]],6]. Every consumer of that data has to re-implement the flattening logic — or worse, iterate naively and get arrays where numbers were expected. The nesting is meaningful to the producer and pure friction for everyone downstream.

Flatten JSON Array removes the friction in one click. Choose how many levels to strip — one, two, or every level down to a completely flat list — and the tool walks the structure, preserving element order and leaving non-array values untouched. Options drop empty arrays and nulls for cleaner output, and the before-and-after element counts make the effect visible immediately. Pretty or compact output, copy or download, all in your browser.

• Three depth modes: One level, two levels, or flatten everything into a single flat list.
• Order preserved: Elements keep their original relative order — only nesting layers are removed.
• Non-array values untouched: Objects, numbers, strings and booleans pass through exactly as they are.
• Drop empty arrays: Remove [] elements instead of keeping them as empty entries.
• Drop nulls: Clean ragged data by removing null elements.
• Before/after counts: Top-level elements in and flat elements out, reported live.
• Pretty or compact output: Choose the output style to match the consumer.
• Copy and download: One click to clipboard or a JSON file.
• Private: All processing happens client-side; nothing is uploaded.

1. Paste a JSON array into the input pane — the input must be an array at its root.
2. Pick the flatten depth: 1 for one layer, 2 for two, or all for a completely flat list.
3. Toggle the cleanups: drop empty arrays and nulls if your data is ragged.
4. Read the result — pretty or compact — and check the before/after counts.
5. Copy or download the flat array.

Example 1 — Aggregation pipeline output. A reporting job groups sales by region and returns [[sales-eu],[sales-us],[sales-ap]] — three arrays, one per region. Flatten depth 1 produces one list of sales records the dashboard can render directly.

Example 2 — Nested category trees. An export of a category hierarchy stores sub-categories as nested arrays. Flatten everything (depth all) produces a single list of every category ID, which a dropdown then renders flat.

Example 3 — Batched uploads. A sync job wraps each batch of records in its own array: [[rec1,rec2],[rec3]]. Depth 1 merges all batches into one list ready for deduplication and import.

Example 4 — Ragged matrix cleanup. A matrix export contains empty rows and null cells. Flatten with drop-empty-arrays and drop-null on produces a clean list of the values that actually exist.

• One click to a usable list: No more hand-rolled flattening logic in every consumer.
• Predictable order: Element order is preserved exactly, so behaviour never changes silently.
• Cleaner downstream data: Drop options remove the ragged edges before processing.
• Visible results: Before/after counts confirm the transformation at a glance.
• Private and instant: Client-side processing, live preview, no uploads.