503-frameworks-micronaut-validation

name: 503-frameworks-micronaut-validation description: Use when you need to design, review, or improve validation in Micronaut applications — including Bean Validation on @Controller methods, @Body @Valid, query/path parameter validation, @ConfigurationProperties validation, custom constraints, nested DTO validation, and ExceptionHandler mapping for constraint violations. This should trigger for requests such as Add validation support in Micronaut; Review Micronaut validation rules; Improve request validation in Micronaut REST APIs; Add custom validation constraints in Micronaut; Validate Micronaut configuration properties. Part of cursor-rules-java project license: Apache-2.0 metadata: author: Juan Antonio Breña Moral version: 0.16.0

Micronaut Validation Guidelines

Apply Micronaut validation best practices at HTTP API boundaries.

What is covered in this Skill?

• Bean Validation annotations on DTOs and command models
• @Valid / @Validated usage in Micronaut controllers
• Validation groups and custom validators
• Consistent mapping of validation failures to 400 responses
• Safe and predictable validation error payloads

Scope: Apply recommendations based on the reference rules and good/bad examples.

Constraints

Before applying validation changes, ensure the project compiles. After improvements, run full verification.

• MANDATORY: Run ./mvnw compile or mvn compile before applying any change
• SAFETY: If compilation fails, stop immediately
• VERIFY: Run ./mvnw clean verify or mvn clean verify after applying improvements
• BEFORE APPLYING: Read the reference for detailed rules and examples

When to use this skill

• Add validation support in Micronaut
• Review Micronaut validation rules
• Improve request validation in Micronaut REST APIs
• Add custom validation constraints in Micronaut
• Validate Micronaut configuration properties
• Improve constraint violation handling in Micronaut

Workflow

1. Read reference and assess project context

Read references/503-frameworks-micronaut-validation.md and inspect the current project setup before proposing changes.

2. Gather scope and decide target improvements

Identify requested outcomes, constraints, and the minimum safe set of changes to apply.

3. Apply framework-aligned changes

Implement or refactor validation-related configuration/code following the reference patterns and project conventions.

4. Run verification and report results

Execute appropriate build/tests and summarize what changed, what was verified, and any follow-up actions.

Reference

For detailed guidance, examples, and constraints, see references/503-frameworks-micronaut-validation.md.