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Skills are curated knowledge packages that teach agents how to do specific things well. Each skill is a structured Markdown file with routing rules and reference patterns. Agents discover skills at startup and load full content only when relevant — no tokens wasted on unused knowledge. Skills follow the SkillsJars specification and work in any agentic CLI — Loopy, Claude Code, and 40+ others.

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Spring Testing Skills

The first production-ready SkillsJars collection — 7 skills that teach agents how to test Spring applications.
SkillDomain
spring-testing-routerMeta-skill — routes to the right domain skill based on the task
spring-jpa-testing@DataJpaTest, Testcontainers, @ServiceConnection, Hibernate 6/7, lazy loading
spring-mvc-testing@WebMvcTest, MockMvc, jsonPath, request validation, @RestControllerAdvice
spring-security-testing@WithMockUser, CSRF, JWT, OAuth2, @PreAuthorize method security
spring-webflux-testing@WebFluxTest, WebTestClient, StepVerifier, virtual time, SSE
spring-websocket-testingSTOMP/WebSocket, WebSocketStompClient, BlockingQueue pattern
spring-testing-fundamentalsAssertJ, BDDMockito, ArgumentCaptor, context caching, anti-patterns

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Skill Structure

Each skill has a SKILL.md with metadata and routing rules, plus a references/ directory with detailed patterns: 
skills/spring-jpa-testing/
├── SKILL.md                       # Metadata + routing rules
└── references/
    ├── testcontainers.md          # Detailed patterns
    ├── transactional-tests.md
    ├── lazy-loading-tests.md
    └── hibernate-6-migration.md

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Install

git clone https://github.com/spring-ai-community/spring-testing-skills.git
cd spring-testing-skills
./mvnw package
mvn skillsjars:extract -Ddir=~/.claude/skills
Skills are extracted to ~/.claude/skills/ where any agentic CLI discovers them automatically.

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Evidence

In the Code Coverage v2 experiment, adding testing skills:
  • Reduced JAR_INSPECT tool calls from 11.0% → 1.0% — the agent stopped inspecting dependencies because the skills already provided the knowledge
  • Reduced expected steps by 25% (224 vs 301) compared to baseline
This validates the thesis: curated knowledge improves agent quality more than model upgrades.

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Creating Custom Skills

Any Markdown file with YAML frontmatter can be a skill: 
---
name: my-team-conventions
description: Coding conventions for our Spring Boot services
---

# Instructions

When working on this codebase:
- Use constructor injection, never field injection
- All REST endpoints return ProblemDetail for errors (RFC 9457)
- Tests use @WebMvcTest with MockMvc, not @SpringBootTest
Place in .claude/skills/my-conventions/SKILL.md (project) or ~/.claude/skills/my-conventions/SKILL.md (global).

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Documentation

Spring Testing Skills

7 skills with routing table and reference patterns

SkillsJars Spec

The SkillsJars format — portable domain knowledge for any agentic CLI