Pydantic

What it does

Pydantic lets you define what your data should look like using Python classes and then validates incoming data against that shape. FastAPI uses it under the hood for request/response validation.

When to use it

Use this when you need to validate or parse structured data in Python — especially API inputs/outputs.

Real example

Your FastAPI endpoint receives JSON from a frontend form and you need to validate it before saving to the DB. Prompt: 'Define a Pydantic BaseModel called NewUserForm with name: str, email: EmailStr, age: int = Field(ge=18). Use it as the type hint in your FastAPI POST route. FastAPI will auto-validate and return 422 errors if invalid.'

Good to know

If you're using FastAPI, you're already using Pydantic. It's also great for validating LLM outputs.

Alternatives

Install

Use cases

Language

Category

Database & backend