Simple user object
A basic object that maps to a single Pydantic model.
{
"id": 1,
"name": "Ada Lovelace",
"active": true
}Code generation tool
JSON to Pydantic v2 Model Generator
Paste JSON objects or arrays and generate Pydantic v2 BaseModel classes with nested models, aliases for invalid or converted keys, Optional fields for null values, warnings, and an optional FastAPI snippet.
This tool runs locally in your browser. Your input is not uploaded.
No uploadsNo server logsNo runtime APIsBrowser-only transforms
Basic scalar fields become str, int, and bool annotations.
Generated output
Generate a Pydantic model to see Python output.
Options
List syntax: builtin list[str]
Examples
Example input and output
camelCase keys become snake_case fields with aliases and null values become Optional fields.
{
"userId": 123,
"displayName": "Grace Hopper",
"email": null
}How it works
- What this tool does: parses JSON locally and generates Pydantic v2 BaseModel classes without server calls.
- How JSON type inference works: strings, integers, floats, booleans, nulls, arrays, and nested objects are inferred from example values.
- Common edge cases: empty arrays, mixed arrays, invalid identifiers, camelCase keys, and deeply nested objects generate visible warnings.
Limitations
- Inference is based on example JSON values, not a full JSON Schema contract.
- Mixed arrays fall back to list[object] because a single precise item type is not available.
- The generated Python is intended as a strong starting point and should be reviewed before production use.
FAQ
Does the JSON to Pydantic tool upload my JSON?
No. Parsing, inference, and code generation all run locally in your browser.
Does it support Pydantic v2 aliases?
Yes. When field names are converted or invalid as Python identifiers, the tool can emit Field aliases for the original JSON keys.
Can it generate a FastAPI example?
Yes. Enable the FastAPI snippet option to add a second output tab with a minimal endpoint example.