JSON Unflatten Free Online Tool 2026

Last updated March 22, 2026

Example: Array Reconstruction

// Input (flat with bracket notation):
{
  "order.id": "ORD-001",
  "order.items[0].product": "Widget",
  "order.items[0].qty": 2,
  "order.items[0].price": 10.00,
  "order.items[1].product": "Gadget",
  "order.items[1].qty": 1,
  "order.items[1].price": 25.00
}

// Output (nested with arrays):
{
  "order": {
    "id": "ORD-001",
    "items": [
      { "product": "Widget", "qty": 2, "price": 10.00 },
      { "product": "Gadget", "qty": 1, "price": 25.00 }
    ]
  }
}

Example: Environment Variables to Config

// Input (environment variable style):
{
  "DATABASE_HOST": "localhost",
  "DATABASE_PORT": "5432",
  "DATABASE_NAME": "myapp",
  "DATABASE_CREDENTIALS_USER": "admin",
  "DATABASE_CREDENTIALS_PASSWORD": "secret",
  "SERVER_PORT": "8080",
  "SERVER_DEBUG": "true"
}

// Output (nested config, delimiter: underscore):
{
  "DATABASE": {
    "HOST": "localhost",
    "PORT": "5432",
    "NAME": "myapp",
    "CREDENTIALS": {
      "USER": "admin",
      "PASSWORD": "secret"
    }
  },
  "SERVER": {
    "PORT": "8080",
    "DEBUG": "true"
  }
}

Example: Elasticsearch Flat Query to Nested

// Elasticsearch uses dot notation for nested field queries.
// Input (flat Elasticsearch field names):
{
  "user.name": "Alice",
  "user.email": "alice@example.com",
  "user.address.city": "New York",
  "metadata.created_at": "2024-01-15",
  "metadata.version": 2
}

// Output (nested JSON document):
{
  "user": {
    "name": "Alice",
    "email": "alice@example.com",
    "address": {
      "city": "New York"
    }
  },
  "metadata": {
    "created_at": "2024-01-15",
    "version": 2
  }
}

Example: CSV Headers to Nested JSON

// CSV with dot-notation headers:
// user.name,user.email,address.city,address.zip
// Alice,alice@example.com,New York,10001

// Parsed as flat JSON:
{
  "user.name": "Alice",
  "user.email": "alice@example.com",
  "address.city": "New York",
  "address.zip": "10001"
}

// Unflattened:
{
  "user": {
    "name": "Alice",
    "email": "alice@example.com"
  },
  "address": {
    "city": "New York",
    "zip": "10001"
  }
}

Example: Type Inference

// Input (all values as strings — common from env vars or CSV):
{
  "server.port": "8080",
  "server.debug": "true",
  "server.timeout": "30",
  "server.ratio": "0.75",
  "server.name": "myapp",
  "server.tags": "null"
}

// Output (with type inference enabled):
{
  "server": {
    "port": 8080,       // "8080" → number
    "debug": true,      // "true" → boolean
    "timeout": 30,      // "30" → number
    "ratio": 0.75,      // "0.75" → number
    "name": "myapp",    // stays string
    "tags": null        // "null" → null
  }
}

// Output (with type inference disabled — all strings preserved):
{
  "server": {
    "port": "8080",
    "debug": "true",
    "timeout": "30",
    "ratio": "0.75",
    "name": "myapp",
    "tags": "null"
  }
}

Delimiter Options

// Same flat data with different delimiters:

// Dot notation (default):
{ "user.name": "Alice", "user.age": 30 }
→ { "user": { "name": "Alice", "age": 30 } }

// Double underscore:
{ "user__name": "Alice", "user__age": 30 }
→ { "user": { "name": "Alice", "age": 30 } }

// Forward slash:
{ "user/name": "Alice", "user/age": 30 }
→ { "user": { "name": "Alice", "age": 30 } }

// Custom separator (e.g., ":"):
{ "user:name": "Alice", "user:age": 30 }
→ { "user": { "name": "Alice", "age": 30 } }

Handling Keys with Dots in Names

// Problem: key "version.1.0" should not be split
// Input:
{
  "config.version.1.0": "stable",
  "config.name": "myapp"
}

// Without escape: splits on all dots
{
  "config": {
    "version": { "1": { "0": "stable" } },
    "name": "myapp"
  }
}

// With escape character (\):
// Input: { "config.version\\.1\\.0": "stable", "config.name": "myapp" }
// Output:
{
  "config": {
    "version.1.0": "stable",
    "name": "myapp"
  }
}

Paste your flat JSON with dot-notation keys to reconstruct the original nested structure. Configure the delimiter and type inference options to match your data source's format.

// Input (flat):
{
  "user.name": "Alice",
  "user.age": 30,
  "user.address.city": "New York",
  "user.address.zip": "10001",
  "user.address.country": "US"
}

// Output (nested):
{
  "user": {
    "name": "Alice",
    "age": 30,
    "address": {
      "city": "New York",
      "zip": "10001",
      "country": "US"
    }
  }
}