The Zero-Schema Mismatch: Type Safety with FastApi and Next.js

Nov 15, 2025

One of the most expensive context switches in modern full-stack development is the mental leap between backend models and frontend interfaces. In the AI engineering space, this gets even messier. You have Pydantic models validating LLM outputs on the server, and TypeScript interfaces handling UI state on the client.

At DevDash Labs, we realized that manually syncing these two worlds was a recipe for production bugs.

The Problem

When an AI agent returns a complex, nested JSON structure (like our market signal reports in Identifi), a single mismatch in a field name can crash the entire UI.

The Solution

We implemented a strict "Contract-First" architecture. By leveraging tools that auto-generate TypeScript definitions directly from our Pydantic models, we achieved a "Zero-Schema Mismatch" environment.

If the backend engineer changes a field from lead_score to priority_score, the frontend build fails immediately. This isn't just error prevention; it's documentation that never goes stale.

In this post, I'll walk through how we set up this pipeline and why I believe "Type Safety" is actually a form of "User Experience."

Gopal Khadka