303-frameworks-spring-boot-validation

name	303-frameworks-spring-boot-validation
description	Use when you need to design, review, or improve validation in Spring Boot applications — including Bean Validation on request DTOs, @Valid/@Validated at API boundaries, constraint groups, custom constraints, @ConfigurationProperties validation, nested DTO validation, and consistent validation error handling. This should trigger for requests such as Add validation support in Spring Boot; Review Spring Boot validation rules; Improve request validation in Spring Boot REST APIs; Add custom Bean Validation constraints in Spring Boot; Validate configuration properties in Spring Boot. Part of cursor-rules-java project
license	Apache-2.0
metadata	{"author":"Juan Antonio Breña Moral","version":"0.16.0"}

Spring Boot Validation Guidelines

Apply Spring Boot validation best practices at API boundaries.

What is covered in this Skill?

• Bean Validation annotations on DTOs and command models
• @Valid / @Validated on controllers and method parameters
• Validation groups for create/update workflows
• Custom constraint annotations and validators
• Consistent 400 error responses for validation failures

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 Spring Boot
• Review Spring Boot validation rules
• Improve request validation in Spring Boot REST APIs
• Add custom Bean Validation constraints in Spring Boot
• Validate configuration properties in Spring Boot
• Improve nested DTO validation in Spring Boot

Workflow

1. Read reference and assess project context

Read references/303-frameworks-spring-boot-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/303-frameworks-spring-boot-validation.md.