NestJS 12 Released with ESM Packages, Standard Schema Validation, and Observability SDK

ESM Transition and Tooling Updates

NestJS version 12 moves its core packages to ESM, while maintaining compatibility for existing CommonJS applications through Node.js's `require(esm)` support. This change necessitates Node.js 20.19+ or 22.12+. New projects generated with `nest new` can now choose between CJS or ESM, with ESM projects defaulting to Vitest and oxlint. Rspack replaces webpack as the monorepo bundler. Benchmarks indicate this transition is primarily a tooling cleanup rather than a performance gain.

Enhanced Schema Validation

The update significantly improves validation ergonomics. Route decorators like `@Body()`, `@Query()`, and `@Param()` now accept a `schema` option, allowing direct use of any Standard Schema compatible object from libraries such as Zod, Valibot, and ArkType without third-party wrappers. `class-validator` remains the default documented option. This approach allows developers to choose their preferred validation library while reducing boilerplate.

Official Observability SDK

NestJS 12 introduces `@nestjs/observe`, an official observability SDK that integrates with the framework's lifecycle to report traces in terms of controllers and providers. This SDK offers richer context compared to patching the HTTP server. However, it is specific to NestJS, lacks out-of-the-box cross-stack correlation, and may lead to framework-level vendor lock-in. A new `nest deploy` command, which forwards to the Mau platform, also points towards first-party services.

Upgrade Process and Other Changes

Upgrading from NestJS v11 involves installing the latest CLI and running `nest upgrade`. This command updates all `@nestjs/*` packages to v12, bumps TypeScript to v6, and applies mechanical changes such as switching from GraphQL Playground to GraphiQL and updating to the NATS v3 client.