OpenAPI with utoipa + Axum utoipa provides compile-time OpenAPI documentation for Rust REST APIs. Code-first approach: annotate handlers and types, get OpenAPI 3.1 spec automatically. Core Concepts 1. ToSchema — Derive for request/response body types 2. #[utoipa::path] — Annotate handlers with path, method, params, responses 3. OpenApi — Combine all paths and schemas into spec 4. Scalar — Serve interactive API documentation Cargo.toml Setup ToSchema — Request/Response Types #[utoipa::path] — Documenting Handlers OpenApi — Combining Everything Serving Scalar UI IntoParams — Query Parameters En…