kotlin-backend-agent-skills

Design reproducible build, image, and deployment pipelines for Kotlin plus Spring applications, including CI verification, layered containers, rollout safety, and deployment-time migration coordination. Use when creating or improving Dockerfiles, CI workflows, image hardening, Kubernetes manifests, release gates, or deployment strategies for Spring Boot services, especially where build reproducibility and operational safety matter.

Design and diagnose Spring configuration, profiles, and `@ConfigurationProperties` binding for Kotlin applications. Use when property binding fails, environment-specific overrides behave unexpectedly, profile layering is confusing, secrets or defaults are modeled unsafely, or Kotlin nullability and constructor binding semantics make configuration errors hard to detect.

Diagnose and resolve Gradle and Spring classpath conflicts, version drift, and binary incompatibilities in Kotlin applications. Use when `NoSuchMethodError`, `ClassNotFoundException`, linkage errors, duplicate logging bindings, Jackson or Hibernate mismatches, or BOM-versus-explicit-version conflicts appear, and the fix must respect the repository's real version authorities.

Decompose business scope into bounded contexts, module or service boundaries, workflows, and API contracts before implementation begins. Use when shaping a new feature, service, or major redesign; when requirements are underspecified; when consistency, idempotency, and integration boundaries must be made explicit; or when ADR-quality tradeoff reasoning is needed for Kotlin plus Spring systems.

Design and implement consistent API validation and error-handling behavior for Kotlin plus Spring services. Use when defining error payloads, mapping framework and domain exceptions, standardizing HTTP status codes, adding `@ControllerAdvice`, preventing internal-detail leakage, or ensuring clients can rely on stable machine-readable error semantics across endpoints.

Generate, debug, and repair Kotlin + Spring Gradle builds with minimal, compatible changes. Use when `build.gradle.kts` or `settings.gradle.kts` is failing, plugins or toolchains are incompatible, dependency management is drifting from the Spring Boot BOM, test or runtime classpaths are broken, or a Kotlin DSL patch must be safe and incremental.

Design resilient HTTP, messaging, and scheduled integrations for Kotlin plus Spring services with explicit timeout budgets, retries, idempotency, circuit breakers, DLQ behavior, and failure observability. Use when integrating with unstable external systems, designing retry logic, handling duplicate delivery, preventing thundering herds, or making message-driven and scheduled workflows safe in production.

Diagnose and design JSON serialization and deserialization behavior for Kotlin plus Jackson in Spring applications. Use when DTOs fail to deserialize, default parameters or nullability behave unexpectedly, date-time or enum formats drift, polymorphic payloads are involved, PATCH semantics must distinguish null from absent, or ObjectMapper changes risk breaking existing API or message contracts.

Migrate Java code to Kotlin in Spring-based codebases without changing behavior, public contracts, framework compatibility, or binary assumptions unless explicitly intended. Use when converting classes incrementally, replacing Lombok patterns, managing platform types and nullability, preserving JPA and proxy behavior, or planning the safe migration order of a mixed Java and Kotlin codebase.

Model Kotlin persistence code correctly for Spring Data JPA and Hibernate, including entity design, relationships, fetch plans, repository queries, lazy loading, and common performance traps. Use when creating or reviewing entities and repositories, diagnosing N+1 or `LazyInitializationException`, placing indexes and uniqueness rules, or preventing Kotlin-specific ORM bugs such as `data class` entities and broken `equals` or `hashCode`.

Refactor Kotlin code toward clearer, more idiomatic design without breaking Spring behavior, serialization, persistence, or public contracts. Use when Java-flavored Kotlin needs cleanup, domain modeling should become more expressive, or boilerplate should be reduced, but the refactoring must remain safe for proxies, Jackson, JPA, configuration binding, and existing tests.

Diagnose and prevent Kotlin plus Spring proxy failures around `@Transactional`, `@Cacheable`, `@Async`, method security, retry, configuration proxies, and JPA entity requirements. Use when AOP annotations appear to do nothing, transactional or cache behavior is inconsistent, compiler plugins may be missing, self-invocation is suspected, or Kotlin final-by-default semantics may break Spring behavior.

Design actionable observability for Kotlin plus Spring services across logs, metrics, tracing, and health endpoints. Use when instrumenting a service, improving incident diagnosis, defining SLO-driven metrics and alerts, adding trace propagation, controlling metric-cardinality cost, or ensuring async and coroutine flows remain observable in production.

Analyze and improve performance, throughput, latency, and concurrency behavior in Kotlin plus Spring services using real evidence from metrics, traces, SQL, thread or heap signals, and code paths. Use when endpoints are slow, pools saturate, coroutines or reactive flows block unexpectedly, N+1 or contention appears, or caching and parallelism decisions need precise, non-generic guidance.

Guide production incident response for Kotlin plus Spring services from first alert through mitigation, diagnosis, and follow-up. Use when error rates spike, latency degrades, capacity saturates, a bad deploy or config change is suspected, or the team needs reversible mitigation first and deeper root-cause work second.

Inspect a Kotlin + Spring repository before making changes or answering implementation, debugging, build, architecture, or review questions. Use when the agent must map modules, Spring Boot/Kotlin/Gradle/JDK versions, compiler plugins, profiles, dependencies, runtime stack, and architectural boundaries so later advice stays compatible with the real project.

Plan safe database schema evolution and zero-downtime change rollout for Kotlin plus Spring systems using Flyway, Liquibase, or equivalent migration tooling. Use when changing tables, columns, constraints, indexes, or data shape in systems with live traffic, rolling deploys, large datasets, or backward-compatibility requirements between old and new application versions.

Diagnose Spring application context startup failures, bean graph problems, missing or duplicate beans, circular dependencies, conditional auto-configuration mismatches, and profile-related wiring issues in Kotlin + Spring projects. Use when the app does not start, a bean is not created or is created unexpectedly, auto-configuration behaves strangely, or a minimal DI fix is needed instead of a broad rewrite.

Review Kotlin + Spring changes for behavioral regressions, transaction and proxy bugs, API and serialization mistakes, persistence risks, security issues, configuration drift, and missing tests. Use when reviewing a PR, diff, patch, or design change where generic style-focused review would miss Spring-specific correctness and operational risks.

Design and generate Kotlin Spring HTTP APIs with correct controller signatures, DTOs, validation, serialization assumptions, error handling, and web tests. Use when building or changing REST endpoints, choosing between MVC and WebFlux, modeling request and response payloads, standardizing error responses, or avoiding Kotlin-specific validation and Jackson mistakes.

Design and audit Spring Security configurations for Kotlin plus Spring services, including filter chains, JWT or OAuth2 resource server setup, method security, CORS, CSRF rationale, and public endpoint exposure. Use when adding or reviewing authentication and authorization, narrowing access rules, validating token handling, or checking for insecure defaults and accidental exposure.

Diagnose Kotlin + Spring failures from stack traces, startup logs, runtime logs, and related metric anomalies, then separate root cause from wrapper exceptions and propose safe next steps. Use when the application fails to start, an endpoint crashes, logs are noisy or deeply nested, or the agent must produce both a quick mitigation and a proper long-term fix without guessing.

Design and generate layered Kotlin + Spring tests that balance speed, realism, and regression value across unit, slice, and integration levels. Use when adding coverage for business logic, controllers, repositories, security, serialization, or end-to-end workflows, and when generic AI output would otherwise overuse `@SpringBootTest`, misuse mocks, or ignore MockK and coroutine testing idioms.

Design safe transaction boundaries, rollback behavior, idempotency, locking, and consistency strategies for Kotlin + Spring business workflows. Use when a feature writes to the database, spans multiple repositories, publishes messages, calls external systems, suffers from partial commits or duplicate processing, or needs precise `@Transactional`, propagation, or isolation guidance.

Plan and execute risky Spring Boot, Spring Framework, Kotlin, Gradle, JDK, and major dependency upgrades with explicit compatibility checkpoints and rollback thinking. Use when preparing or diagnosing a major version jump, navigating `javax` to `jakarta`, K2 adoption, plugin compatibility, auto-configuration drift, behavior changes in Hibernate or Security, or project-specific upgrade sequencing.