Use when asked to review, check or diagnose Spring Boot code: a pull request, diff, module or file before it merges; a slow endpoint or query (N+1, unbounded reads, JPA and Hibernate performance); security, JSpecify null-safety, architecture boundaries or Boot 4 migration risks in existing code; or whether the tests would catch real bugs, proving each finding by running it. Not for Kotlin-only code, non-Spring frameworks, or generic review advice without code context.

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Use when starting a new Spring Boot project or service: scaffolding or bootstrapping a backend, REST API, microservice or modular monolith; choosing how to structure it (layered, package-by-module, modular monolith, tomato, DDD-hexagonal); selecting Spring Boot 4 features; generating the base project with progen or Spring Initializr; or applying the bundled templates and references in this skill. Not for migrating existing projects or for isolated JPA/repository work without broader project-creation context.

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Writes a Flyway database migration for this project following the team's rules for naming, editing and renaming, so migrations from different developers don't collide and deployed databases stay valid. Use whenever a change needs a new table, column, index or data fix, or the user mentions a schema change or migration.

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Use when a team wants every developer's coding agent (Claude Code or Codex) to follow the same rules on a Maven Spring Boot 4 repository: setting up AGENTS.md, guardrails, shared agent settings, or build and CI checks that agents must pass before code merges. It adds ./mvnw verify gates that fail on null-safety bugs (NullAway with JSpecify), module-boundary breaches (Spring Modulith), unknown or deprecated Boot property keys, Spring mistakes that compile (ArchUnit) and unformatted code, Claude Code hooks that run those gates before a turn ends, and a CI workflow.

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Use when upgrading an existing Spring Boot application, for example from Boot 3.x to Boot 4 or to the latest Spring Boot and Java: dependency transitions and starter renames, test annotations such as @MockBean to @MockitoBean, Jackson 3 issues, Spring Modulith 2 or Testcontainers 2 upgrades, code that stops compiling after a version bump, or planning a phased migration. Not for greenfield project creation or isolated repository design.

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Use when writing or adding tests for Spring Boot code at a service's edges: HTTP clients that call other services (WireMock: 4xx and 5xx responses, timeouts, retries), Kafka or RabbitMQ listeners (redelivery, poison messages, dead-letter topics), events published to other services, or full-API tests against real databases with Testcontainers; also when a Boot 4 test needs the right imports, slices or container wiring. Supplies verified Boot 4.1 templates and the framework traps that make such tests pass without proving anything. Not for reviewing existing tests (see code-reviewer) or Boot 3 to 4 test migration (see springboot-migration).

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