JSON to Pydantic V2 Converter (FastAPI Ready)
Instantly convert JSON objects into Pydantic V2 (BaseModel) classes. Automatically generates Field(alias="...") for API compatibility, handles Snake_Case conversion, and strictly types deeply nested lists (e.g., List[Optional[int]]). Perfect for pasting directly into FastAPI payloads.
Why use Pydantic Models?
Pydantic is the standard for data validation in modern Python (used by FastAPI, LangChain, etc.). Unlike plain dictionaries, Pydantic models guarantee the types and structure of your data.
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Type Safety
id: int
IDE autocomplete works perfectly. No more
KeyErrorsurprises. -
Validation
email: EmailStr
Automatically validates emails, URLs, and custom constraints.
Advanced Pydantic Features
1. Handling "Invalid" JSON Keys
Field(alias=...)JSON keys often contain dashes (user-id) which are invalid in Python. Use logical names with aliases.
from pydantic import BaseModel, Field
class User(BaseModel):
# JSON: {"user-id": 123}
user_id: int = Field(alias="user-id")
2. Optional Fields
typing.OptionalIf a field might be missing or null, mark it as Optional.
from typing import Optional
class Product(BaseModel):
description: Optional[str] = None
3. Export to JSON Schema
model_json_schema()Need to share your API spec? Pydantic can auto-generate the JSON Validation Schema.
schema = User.model_json_schema() print(json.dumps(schema, indent=2))
Pro Features & Integrations
🛠️ Custom Validators
Enforce logic, like "positive numbers only".
from pydantic import field_validator
@field_validator('age')
def check_age(cls, v):
if v < 0:
raise ValueError('Must be positive')
return v
⚡ FastAPI Integration
Use your model directly in routes.
from fastapi import FastAPI
app = FastAPI()
@app.post("/users/")
async def create_user(user: User):
return user
Technical Deep Dive: V2 Performance & Safety
🔒 Strict Mode
By default, Pydantic coerces types (e.g., string "123" → int 123). for 100% type safety, use Strict Mode.
class Config:
strict = True
# Or at runtime:
User.model_validate(json_data, strict=True)
🚀 High-Performance Serialization
Pydantic V2 (Rust core) allows extremely fast JSON dumping.
user = User(id=1, name="Alice") # Dump to dict data = user.model_dump() # Dump to JSON string (Faster!) json_str = user.model_dump_json()
Dealing with messy Python dicts?
Convert basic Python dictionary syntax to valid JSON first.
➡️ Python Dict to JSON Tool