JSON to Pydantic Model Generator Online — Free Python Tool
JSON to Pydantic Model
Convert JSON to Pydantic v2 BaseModel classes for Python and FastAPI.
Free online JSON to Pydantic model generator. Paste any JSON object or array and get Python Pydantic BaseModel classes with proper type annotations, Optional[T] for nullable fields, List[T] for arrays, datetime for date strings, and Field aliases for non-snake_case keys. Supports both Pydantic v1 and v2. Perfect for FastAPI, Django, and Python developers. Runs entirely in your browser.
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Tags: json, python, pydantic, fastapi, model, converter, generator
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How to JSON to Pydantic Model Online
Paste valid JSON into the input area on the left.
Set the root model name (defaults to 'Root') using the option field.
Choose the Pydantic version: v1 or v2.
Toggle field aliases to generate Field(alias=...) for JSON keys that differ from Python naming conventions.
Click Convert or press ⌘↵ (Mac) / Ctrl+Enter (Windows) to generate Pydantic models.
Copy the generated Python code or download it as a .py file.
JSON to Pydantic Model Features
Generates Pydantic v1 and v2 BaseModel classes from any JSON object or array.
Supports nested objects — creates separate named models for each nested structure.
Smart type inference: str, int, float, bool, None, List[T], Optional[T], and nested model types.
Optional Field(alias=...) for snake_case Python names that map to camelCase JSON keys.
Pydantic v2 mode uses model_config = ConfigDict(populate_by_name=True) for alias support.
Correct Optional[T] for nullable fields.
Works entirely in your browser — JSON never leaves your device.
Keyboard shortcut ⌘↵ for instant conversion.
Frequently Asked Questions
- What is Pydantic?
- Pydantic is the most widely used Python data validation library. It uses Python type annotations to define data models and validates input at runtime. Pydantic v2 was rewritten in Rust for a significant performance boost.
- What is JSON to Pydantic conversion?
- JSON to Pydantic generates Pydantic BaseModel class definitions from a JSON sample. Instead of writing models by hand, paste your API response and get strongly-typed Python code with correct field types and optional validation.
- Should I use Pydantic v1 or v2?
- Use v2 for new projects — it is faster, more feature-rich, and actively developed. Use v1 if you are working on an existing codebase that has not yet migrated. FastAPI supports both.
- What are field aliases?
- Field aliases let you use Python-idiomatic snake_case attribute names in your model while still parsing JSON with camelCase keys. For example, Field(alias='firstName') maps the JSON key firstName to a Python attribute first_name.
- Is my JSON data safe?
- All conversion runs in your browser using pure JavaScript. No JSON is ever sent to a server. Your data stays completely private.
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