Candid, a company offering an API for medical billing, faced challenges with repetitive code writing and synchronization issues across multiple sources of truth, leading to runtime bugs and inefficiencies. By adopting Fern's schema-first API development approach, Candid streamlined its processes significantly. Engineers first define schemas using yaml files similar to OpenAPI, then generate necessary backend components like Pydantic models and FastAPI routes with Fern, which integrates with mypy for compile-time error checking. Once business logic is implemented and merged, Fern automatically generates a TypeScript client for the frontend, ensuring consistency and reducing boilerplate code. This approach has resulted in 95,000 lines of backend and 30,000 lines of frontend code being auto-generated, minimizing wasted engineering time and establishing a single source of truth for the API. Candid plans to further enhance its operations by using Fern to keep API documentation in sync and to generate customer-facing SDKs, improving integration efficiency.