Pure Frontend · Nested to Flat · Custom Separator · Depth Control · Reversible
Zero Dependencies · Works OfflineWhat Can the JSON Flattener Do?
The JSON Flattener is a pure frontend online tool for converting multi-level nested JSON objects into single-level key-value pair structures. Enter nested JSON, and the tool automatically extracts all deep properties to the top level, using path separators to join nested key names, such as user.address.city. Supports custom separators, maximum flattening depth control, array index preservation, special key escaping, and reverse operation (unflattening flat JSON back to nested structure). All processing happens locally in the browser.
Core Features
- Smart Flattening: Automatically identifies nesting levels, recursively flattening all sub-objects and arrays
- Custom Separators: Supports dot, underscore, slash, hyphen, and custom separators
- Depth Control: Set maximum flattening depth to preserve nested structures below a certain level
- Reversible: Supports unflattening flat JSON back to the original nested structure
- Array Handling: Choose to preserve or ignore array indices
How to Use
Step 1: Select separator and depth control options in the configuration area.
Step 2: Paste nested JSON in the input box, or click "Load Example".
Step 3: Click "Flatten" or use Ctrl+Enter to see the flattened result.
Step 4: Click "Copy Result" or "Download" to export. Use Ctrl+Shift+C for quick copy.
Use Cases
Form Data Processing
Flatten complex nested API responses into form-friendly key-value pairs for HTML form binding and data submission.
Database Storage
Flatten nested JSON into relational database column structures, such as converting MongoDB documents to MySQL rows.
Log Analysis
Flatten nested log JSON for import into ELK and other log systems, enabling full-text search and field filtering.
Config File Conversion
Convert between nested configurations (YAML/JSON) and flat configurations (.env).
Extended Knowledge
JSON flattening (Flatten) uses a recursive algorithm to traverse all object properties, continuing deeper when encountering objects or arrays, and joining paths with separators as new key names. Depth control limits recursion levels. The reverse operation (Unflatten) rebuilds nested structures by parsing separators in key names. In JavaScript, Object.entries() and recursion are common implementation approaches. Flattened JSON is more practical for CSV export, form mapping, and data pivoting scenarios.
FAQ
What is JSON flattening?
JSON flattening converts multi-level nested JSON objects into single-level key-value pairs, using path separators (e.g., .) to join nested keys, such as user.address.city becoming a flat key.
What separators are supported?
Supports dot (.), underscore (_), slash (/), hyphen (-), and custom separators for flexible path representation.
How are arrays handled?
Arrays use indices as keys by default, e.g., items.0.name. You can choose to ignore array indices and only flatten object levels.
Can I reverse the operation?
Yes. Supports unflattening flat JSON back to nested structure, automatically detecting path separators to rebuild object hierarchy.
Is data uploaded to a server?
No. All JSON flattening and unflattening operations happen locally in the browser. Data is never uploaded to any server.
Is depth control supported?
Yes. You can set a maximum flattening depth to only flatten to a specified level, preserving deeper nested structures.