JSON Unflattener

Rebuild nested JSON from flat dot-notation keys.


    

  

  

    
    
    
  

  


    

    

      
ToolsSoup's JSON Unflattener is a free online tool that rebuilds nested JSON from a flat object with dot- and bracket-notation keys. Paste a flat map like user.name or items[0].id and click Unflatten to get back the full nested structure. Everything runs in your browser — no uploads, no sign-up, and nothing ever leaves your device.

      

        
What is JSON unflattening?

        
Unflattening is the reverse of flattening: it takes a single-level object whose keys are paths — such as a.b.c or list[0] — and reconstructs the nested objects and arrays they describe. A dot in a key means a nested object property, and a bracketed number means an array index. Unflattening is handy when a system hands you flat key-value data, like form fields or environment-style settings, that you need to turn back into structured JSON.

        
      

      

        
How to unflatten JSON online

        
Unflattening JSON with ToolsSoup takes just a few seconds:

        
  1. Paste your flattened JSON object into the input box on the left.
  2. Click Unflatten to rebuild the nested objects and arrays.
  3. Copy the nested JSON with one click.

      

      

        
What key notation is expected?

        
Use a dot between object properties (user.name) and square brackets with a number for array items (tags[0]). Paths can mix both, like orders[0].items[1].sku. Values can be any JSON type, and empty objects and arrays are restored exactly. This is the same notation the JSON Flattener produces, so the two tools round-trip cleanly.

        
      

      

        
Why use this JSON unflattener?

        
  • 100% free with no ads, sign-up, or usage limits.
  • Runs entirely in your browser — your data is never uploaded to a server.
  • Rebuilds nested objects and arrays from dot and bracket keys.
  • Round-trips perfectly with the JSON Flattener.
  • Works offline once the page has loaded.

      

      

        
Frequently asked questions

        

          
Is this JSON unflattener free?

          
Yes. Every tool on ToolsSoup is completely free to use, with no account, sign-up, or hidden limits.

        

        

          
What key notation does it expect?

          
Dots separate object properties (a.b) and bracketed numbers mark array indexes (a[0]). A key like user.roles[0].name rebuilds an object, an array, and a nested object in one go.

        

        

          
Is this the reverse of flattening?

          
Yes. The JSON Unflattener undoes what the JSON Flattener does, so you can flatten JSON, edit the flat keys, and unflatten it back to the original nested shape.

        

        

          
What if my input isn't a flat object?

          
The tool expects a single JSON object whose values are the leaf values. If you paste something that is not an object, it shows a clear error so you can fix the input.

        

        

          
Is my data safe?

          
Absolutely. All unflattening happens locally in your browser using JavaScript, so your JSON is never sent to or stored on any server.