What is JSON to Haskell Data Type Generator?
This tool converts JSON data into Haskell data type definitions with automatic type inference. It generates idiomatic Haskell code with proper field naming conventions, nested data types, and deriving clauses for Show and Eq.
How to Use
- Paste your JSON data into the input area
- Click "Generate" to create Haskell data type definitions
- Copy the output and use it in your Haskell project
Why Use This Tool?
Tips & Best Practices
- Use realistic sample data — type inference depends on actual values
- Field names are prefixed with the data type name to avoid name collisions
- Null values are typed as Maybe a for optional fields
- Empty arrays are typed as [a] — you may need to specialize this
Frequently Asked Questions
How are JSON types mapped to Haskell?
JSON strings → String, integers → Int, floats → Double, booleans → Bool, null → Maybe a, arrays → [T], objects → separate nested data types.
Why are field names prefixed?
Haskell record fields share a global namespace. To avoid name collisions, each field is prefixed with the data type name (e.g., userId, userName for User data type).
How are nested objects handled?
Nested JSON objects are converted to separate Haskell data types. They are ordered children-first so that referenced types are defined before the types that use them.
What deriving clauses are added?
All generated data types derive Show and Eq instances, which are the most commonly needed instances for debugging and comparison.
Is my data sent to a server?
No, all processing happens entirely in your browser. Your JSON data never leaves your device.