Spring Boot Skills Marketplace

Claude Code and Codex skills for Spring Boot 4 and Java 25. The main one, spring-boot-team-harness, gives every developer on a team the same agent setup and makes ./mvnw verify (or ./gradlew build) fail on the mistakes agents make. The others create, migrate, test and review Spring Boot projects.

Every skill was trialled with and without it, and content that made no difference was cut. The results are below.

The team harness

scripts/apply_harness.py adds the harness to a Maven project or a single-project Gradle build (Groovy or Kotlin DSL). It adds only what the project lacks, so it works on existing services, on a project in a subfolder, and on top of what progen set up. On Gradle, the gates live in gradle/harness.gradle, which the build file applies with one line. The commands below are Maven's; on Gradle, ./gradlew build runs the same gates. creating-springboot-projects runs it as its last step. Rerun it after updating the plugin.

It steers the agent at three points:

1. Before it starts. AGENTS.md, which both Claude Code and Codex read, describes the repository: modules, how to run and test it, conventions, and how to work (plan larger changes first, write a failing test first for bugs, review before the pull request). The agent drafts the repository-specific sections from the code, and the team corrects them.
2. Before it says it's done. AGENTS.md tells the agent to run ./mvnw verify. A Stop hook runs the gates that need no Docker when a turn ends with changed code, and sends any errors back to the agent. A PreToolUse hook refuses force-pushes, git reset --hard, git clean -f, edits to Flyway migrations already on main, edits to the rule tests and the ArchUnit and Spring Modulith violation records, the record flag baseline.py uses, and any edit to a module's package-info.java, so an agent can't weaken a rule to get its change through. The Stop hook and CI also fail a change that adds a source file over 20 KB (about 5,000 tokens) or grows one, so each file stays small enough for an agent to read whole, and a new numbered copy such as OrderService2, the name a careless split takes. The hook is advisory, so a CI check backs it up.
3. Before merge. A CI workflow runs ./mvnw verify on every pull request, unless one already runs mvnw (./gradlew build and gradlew on Gradle). A second one fails a pull request that weakens a rule, adds to either violation record, widens or removes a module's allowedDependencies or opens the module, or edits an applied migration (narrowing a module's dependencies passes), whichever tool made the change; a maintainer accepts an intended change with the harness-rule-change label. A REVIEW.md at the repository root tells reviewers, the code-reviewer skill and Claude Code's GitHub review alike, what the code doesn't show: the team's own failure rules, which changes are high risk, and what not to report. In a trial, reviewers given the rules found a planted break of one in 6 of 6 reviews, against 0 of 6 without, at the same cost.

./mvnw verify fails on:

• a null-safety bug (NullAway with JSpecify)
• a module-boundary breach (Spring Modulith): a module using another's internal type, a published type whose public constructor takes an internal one, a dependency cycle, a dependency its allowedDependencies leave out, or an allowed dependency it no longer uses
• a Boot property key that no dependency defines, or a deprecated one, since Boot ignores both silently
• code that compiles but breaks at runtime (ArchUnit): a class calling its own @Transactional or @Cacheable method, controllers using repositories or returning JPA entities, @Retryable or @Async that nothing switches on, a transaction held open across an HTTP call, HTTP clients with no timeouts, @ManyToOne left eager, enums stored by position, @ManyToMany mapped as a List, @Autowired fields, Jackson 2 code that Boot 4 ignores, and JUnit 4 or @Disabled tests that never run
• build shortcuts that pass the tests while production lacks the feature: a starter in test scope, spring-boot-autoconfigure-classic, Flyway migrations that Boot 4 never runs, and a schema from ddl-auto instead of the migrations
• unformatted code (Spotless, or the project's own Spring Java Format)
• an email address or credential that the app's code logs during a test (LogLeakCheck)
• printStackTrace, a catch-all handler that reads the exception message, or a hand-built OpenTelemetry bean
• Actuator endpoints such as env exposed on the public port

Each failure message says how to fix it. On an existing codebase, scripts/baseline.py makes verify pass on day one: it marks the classes NullAway rejects today @NullUnmarked, records today's ArchUnit violations with FreezingArchRule, and records today's Spring Modulith boundary violations in modulith_store, keyed by module and type rather than line so the record survives edits. New classes get the full checks, and fixed violations drop out of the record. NullAway skips all of a class marked @NullUnmarked, including code added to it later, until the mark is removed. The Stop hook blocks only on errors in files the session changed.

The harness also commits up to three project skills: add-module (named from the project's glossary, with its allowed dependencies declared up front), move-code (moves classes between modules with OpenRewrite ChangeType and ChangePackage recipes, since agents can't call IntelliJ's move refactoring) and db-migration. It also enables this plugin for every teammate through enabledPlugins and adds no MCP servers.

What each tool gets

Claude Code and Codex run the same two hook scripts: .claude/settings.json registers them for Claude Code and .codex/hooks.json for Codex. Codex runs a project's hooks only after each developer trusts them with /hooks, and asks again whenever .codex/hooks.json changes.

	Claude Code	Codex
Skills	Yes	Yes
AGENTS.md guidance	Yes (through CLAUDE.md)	Yes
Gates checked when a turn ends (Stop hook)	Yes	Yes, once the hooks are trusted
Refusing force-pushes and edits to rules, freeze record and applied migrations (PreToolUse hook)	Yes	Yes, once the hooks are trusted
./mvnw verify gates	Yes	Yes
CI: verify and the integrity check	Yes	Yes

The hooks are advisory in both tools. Make both CI checks required on the main branch: they are the protection every tool shares.

Observability

The harness also adds an observability pack by default, so an agent can check what a running app did, not only what it returned. A page can look right while the server fails behind it.

• Telemetry: Boot sends traces, metrics and logs over OTLP, including SQL spans. Export is off until OTLP_EXPORT_ENABLED=true, and logs are capped at INFO on export. The app only knows an OTLP endpoint, so it doesn't change between a laptop, ECS and EKS.
• Local stack: compose.observability.yml runs Grafana, Prometheus, Tempo and Loki on this machine only, and the observability profile sends everything to it. Boot's Docker Compose support doesn't start it, so you run it when you want it.
• Dashboards: Service health and JVM and resources. observability/check_dashboards.py proves the pipeline and queries work: it fails if a required panel is empty, a panel has only NaN, or no traces arrive. It doesn't prove a change behaved.
• One request: observability/check_request.py sends a request with a fresh trace id and reports its status, spans and ERROR lines. AGENTS.md tells agents to run it before they say a runtime change works. Nothing blocks an agent that skips it.
• Handled failures: HandledFailureFilter logs each 5xx that an @ExceptionHandler answers once, with its cause, including async requests. Handlers can return a generic response without hiding the failure.

The harness doesn't provision a collector or anything else on AWS, and none of this has been run there yet. Each project gets docs/observability.md with the settings and queries.

Why it's built this way

• Rules go in build checks, because instructions in CLAUDE.md are advisory and hooks are deterministic (Claude Code best practices). OpenAI's Codex team enforces architecture with linters whose messages tell the agent how to fix the problem (Harness engineering).
• Fast checks run on every change, slow ones after integration (Birgitta Böckeler, Harness engineering).
• AGENTS.md stays short. OpenAI found one large AGENTS.md failed and keeps theirs to about 100 lines.
• The gates check structure, not behaviour. For behaviour, AGENTS.md asks for a full-API test (the whole app on a random port, with Testcontainers) of each endpoint a change touches.

Install

git clone https://github.com/a-pavithraa/springboot-skills-marketplace.git
cd springboot-skills-marketplace
python3 install.py            # Claude Code
python3 install.py --codex    # Codex

The script needs Python 3.10 or later and is safe to rerun. For Claude Code it installs at user scope and turns on auto-update for this marketplace. For Codex it copies the skill folders into ~/.codex/skills.

Without the script, in Claude Code:

/plugin marketplace add a-pavithraa/springboot-skills-marketplace
/plugin install springboot-architecture@springboot-skills-marketplace

Or copy the folders by hand: cp -r plugins/springboot-architecture/skills/* ~/.claude/skills/ (or ~/.codex/skills/).

Optional third-party skills

The marketplace also lists plugins by other authors, unchanged and pinned to a reviewed commit. Report problems with them to their authors.

Plugin	What it adds	Source
mattpocock-picks	grilling, pr, tdd, diagnosing-bugs, prototype, domain-modeling, handoff, writing-for-agents	mattpocock/skills
html-plan	an implementation plan as one interactive HTML page	claude-plugins-community, by Thariq Shihipar
grill-page	a grilling interview answered through clickable options	build-compass
pstack	technical-writing, unslop, blast-radius, correct and more; Claude Code only	cursor/plugins, by Lauren Tan

python3 install.py --with extras adds the first three, and --with extras,pstack adds all four. GUIDE.md shows how the team workflow uses them.

Skills

Skill	Use it to
spring-boot-team-harness	Add AGENTS.md, build gates, hooks and CI to a project, as described above
creating-springboot-projects	Start a service. It asks about the domain and team, picks an architecture, generates the project with progen or Spring Initializr, and applies the team harness
springboot-migration	Upgrade to Boot 4, Java 25, Spring Modulith 2 and Testcontainers 2. It scans the project, then changes dependencies, code and config in that order
writing-springboot-tests	Test HTTP clients, retries, timeouts, transactions and Kafka listeners, with templates run against Postgres, Kafka and WireMock. Check who may call each route, with test logins that go through the app's own role mapping. Test domain rules as properties over generated inputs
code-reviewer	Review code or tests for Boot 4 changes, architecture fit and performance traps such as N+1 queries. It proves each test finding by breaking the guarded line and showing the test stays green

Claude Code and Codex both load a skill when a request matches its description. To make sure one loads, name it: $code-reviewer review this service in Codex. Automatic loading has been trialled only in Claude Code (Scenario 25).

creating-springboot-projects and code-reviewer cover five architectures, from simplest to most complex: Layered, Package-by-Module, Modular Monolith, Tomato (rich domain with value objects) and DDD+Hexagonal. Start with the simplest that fits.

Trial results

Each trial ran the same task in fresh sessions with and without a skill, and scored the result with planted bugs, PIT mutation scores or Hibernate statement counts. Most ran once per arm, so read them as direction, not proof. Full records are in tests/baseline-results/.

#	Skill	Model	Result	Outcome
10	writing-springboot-tests	default	Both caught the planted bug. The skill raised the PIT score from 98% to 100%, at about twice the tokens	Small gain
11	writing-springboot-tests	Sonnet	Caught 4 to 5 of 5 edge bugs against 1 of 5. The baseline's mocks hid broker bugs, and 3 of its tests failed on correct code	Gain
12	writing-springboot-tests	Sonnet	On edge bugs the skill doesn't name, the baseline caught 4 of 4 and the skill 2 of 4, because the agent copied template shortcuts. The skill now says to take cases from the contract	Loss, fixed
13	code-reviewer (tests)	Sonnet	Both found all 6 defects. The skill proved 3 by running them, the baseline 1	Gain in proof only
14	spring-data-jpa	Sonnet	Same fixes, identical statement counts	No gain, skill retired
15	springboot-migration	Sonnet	Same handling of silent hazards. The skill targeted 4.1 with complete dependencies; the baseline missed a starter 4.1 needs	Small gain
16	creating-springboot-projects	Sonnet	The baseline started on Boot 3. The skill used Boot 4.1 and Testcontainers 2, and added the architecture test once the workflow named it	Gain
17	code-reviewer	Sonnet	Old and trimmed SKILL.md both found 13 of 13 planted issues, with 42% fewer words	No loss from trim
18	code-reviewer (tests)	Sonnet	Proved 16 gaps in a green, well-kept suite	Gain, no comparison arm
19	team harness	Sonnet	With AGENTS.md the agent ran verify and avoided both traps it fell into without. The Stop hook caught nothing extra	Gain from AGENTS.md
20	code-reviewer	Sonnet	The fresh-context review offer appeared only when placed as a step before the review	Works
21	run-app (harness)	Sonnet

Fixtures and run scripts are in tests/fixtures/. tests/README.md explains how to add a trial. The bundled scripts have their own tests, which need no network or Docker:

python3 -m unittest discover -s tests/scripts -v

Prerequisites

• Claude Code or Codex
• Python 3.10 or later for install.py and the skills' scripts. The python3 that ships with macOS is 3.9
• Java 17 or later, Java 25 for new projects. A project with the harness needs JDK 21.0.8 or later, because Error Prone does
• Maven or Gradle
• Docker, for the harness's local Grafana stack
• Optional: progen (go install github.com/sivaprasadreddy/progen@latest)

Credits

• Architecture patterns: Siva Prasad Reddy, from spring-boot-application-architecture-patterns
• Project generator: progen
• Spring Boot 4 features: spring-boot-4-features
• Modular monolith reference: spring-modular-monolith
• Marketplace inspiration: sivalabs-marketplace
• JPA and Hibernate practices: Vlad Mihalcea