How to keep FastAPI and Next.js types synced (without leaking your database schema)

Let's talk about the "full-stack boundary." If you're building a modern web app with a Python backend (FastAPI) and a TypeScript frontend (Next.js/React), you know the pain: keeping your types in sync.

You add a new field to a Pydantic model, you deploy, and ten minutes later your frontend crashes because the Zod validation schema wasn't updated. It's a manual, error-prone process.

The Problem with "Online Converters"

The usual move is to Google "Pydantic to Zod," click a link, and paste your code. This is a security risk. Your Pydantic models map to your database. Pasting them into a random, ad-filled server is a massive privacy gamble.

I decided to build a 100% offline alternative.

Enter SyntaxSnap: 100% Offline Pydantic-to-Zod 🔒

I built SyntaxSnap to be a client-side suite of dev tools. The Pydantic-to-Zod converter runs entirely in your browser. No API calls. No tracking. You can turn off your Wi-Fi and it still works perfectly.

It handles the complex stuff automatically:

• Nested Models: Resolves $ref pointers and $defs.
• Type Inference: Maps Python Enums and Unions (anyOf) to Zod equivalents.
• Constraints: Maps string/number constraints (min/max) to Zod chaining.

How to use it:

1. Generate your JSON schema in Python:
2. Paste that JSON into SyntaxSnap's Converter.
3. Instantly copy your safe, typed Zod schema.

python
from pydantic import BaseModel

class User(BaseModel):
    id: int
    email: str

print(User.model_json_schema())