feat(fastify): add Fastify native schema Validation and Serialization

[vrxj81]

PR Checklist

Please check if your PR fulfills the following requirements:

• [ x ] The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• [ x ] Tests for the changes have been added (for bug fixes / features)
• [ x ] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• [ x ] Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Currently, when using the @nestjs/platform-fastify package, route schemas (e.g., body, querystring, params) cannot be defined via metadata or decorators in a way that integrates with Fastify’s native validation system.

This means:

• Developers must manually register schemas when defining routes.
• There’s no clean or idiomatic NestJS way to leverage Fastify's built-in request validation using schema.body, schema.querystring, etc.
• Nest’s route metadata system (Reflect.getMetadata(...)) does not natively support passing Fastify schemas into route options.

Issue Number: 14986

What is the new behavior?

This change introduces support for Fastify-native schema validation by enabling developers to annotate their route handlers with a new @Schema() decorator.

The FastifyAdapter is extended to read schema metadata from the route handler and inject it into Fastify’s route options using the schema field. This enables full compatibility with Fastify’s schema-based validation, serialization, and tooling.

Example usage:

@Schema({
  body: Type.Object({
    name: Type.String(),
  }),
})
@Post()
create(@Body() dto: any) {
  return dto;
}

his allows seamless integration with libraries like TypeBox, Zod, and others—while remaining agnostic of the schema definition format—and keeps the validation logic cleanly separated from business logic.

Does this PR introduce a breaking change?

• Yes
• [ x ] No

No, this PR does not introduce any breaking changes.

The schema metadata is entirely optional and only applied when the @Schema() decorator is used. Existing applications using the FastifyAdapter without this decorator will continue to behave exactly as before.

Other information

This feature enables native Fastify schema validation support in NestJS by allowing schemas to be defined via a @Schema() decorator and injected into the route options through a modified FastifyAdapter.

It integrates seamlessly into the current architecture, does not interfere with existing applications, and opens the door for using TypeBox or any other schema definition library without coupling to a specific one.

A corresponding issue was opened to describe the motivation and context of this PR: https://github.com/nestjs/nest/issues/

[coveralls]

Pull Request Test Coverage Report for Build f798fff2-b2fb-4ae8-aaa2-264a76cd5ac4

Details

• 5 of 5 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 89.328%

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Totals
Change from base Build a2ecd259-4df8-488c-89b4-98c4c90fbc6b:	0.007%
Covered Lines:	7165
Relevant Lines:	8021

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💛 - Coveralls

[micalevisk]

so this is supposed to close the Issue #14986

Will this address the Issue #14931 as well?

[jadejr]

Any chance a sample could be added to the samples directory? Probably something like https://github.com/nestjs/nest/tree/master/sample/01-cats-app . I ended up using fastify for the first time with nest so i never got into how things might work with plain fastify app.

[vrxj81]

Any chance a sample could be added to the samples directory? Probably something like https://github.com/nestjs/nest/tree/master/sample/01-cats-app . I ended up using fastify for the first time with nest so i never got into how things might work with plain fastify app.

That should be easily doable. but then in the sample/10-fastify example.

[kamilmysliwiec]

Duplicate #14789