fastify

Schema validation in Fastify 5 requires defining full JSON Schema for routes and configuring a TypeScript Type Provider to automatically infer request and response types. This approach ensures type-safe APIs with automatic validation and serialization.

Fastify plugin encapsulation isolates decorators by default, so shared decorators require using fastify-plugin to hoist scope. Without fastify-plugin, parent scopes cannot access child decorators, breaking route wiring and shared utility access.

Webhook HMAC verification requires capturing the raw request body before JSON parsing to hash the original payload. In Fastify 5, this involves specific raw-body plugin configuration to ensure the signature matches the unmodified payload.

Migrating from Fastify 4 to 5 requires updating lifecycle hook ordering, applying strict response schemas for every public route, and removing forbidden patterns like calling register() inside handlers to maintain production-grade stability.

Yes, you can test Fastify 5 API routes using the built-in app.inject method. This function simulates HTTP requests internally, allowing you to validate schema-driven endpoints, error mapping, and lifecycle behavior without network overhead.

Yes, Fastify 5 enforces strict production rules requiring response schemas for every public route. Defining full JSON Schema for outputs ensures proper response serialization, secure error mapping, and prevents unexpected data leakage.