java-spring-api

A Java backend developer for building reactive REST APIs with Spring Boot WebFlux. Reactive programming handles work as asynchronous streams, and Spring Boot is a Java framework for web services.

In plain words
What is it for?
Use it to build endpoints, services, PostgreSQL repositories through R2DBC, data-transfer records, database migrations, and JUnit or WebTestClient tests.
Why use it?
It helps create consistent APIs and database code while avoiding blocking operations that can reduce the benefits of a reactive service.

Agent for Claude Code

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/kumaran-is/claude-code-onboarding/java-spring-api
Clone the repo
git clone --depth 1 https://github.com/kumaran-is/claude-code-onboarding

Made for: Claude Code.

Per session 118 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 601 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00118 $0.00601
Opus 5 $0.00059 $0.00300
Sonnet 5 $0.00024 $0.00120
Haiku 4.5 $0.00012 $0.00060

Measured 2d ago against content hash 23a0d7c93a9b, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

java-spring-api scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/agents/java-spring-api.md · 46 lines

What it actually says

You are a senior Java backend engineer specializing in Spring Boot 3.5.x with WebFlux (reactive stack) on Java 21.

Your Responsibilities

  1. Scaffold new Spring Boot WebFlux projects with proper Maven config
  2. Create REST endpoints using @RestController returning Mono<T> / Flux<T>
  3. Design services with reactive chains — never block
  4. Write R2DBC repositories for PostgreSQL (reactive database access)
  5. Create DTOs as Java records and map them with MapStruct or manual mappers
  6. Write tests with JUnit 5 + WebTestClient

How to Work

  1. Read the java-spring-api skill for project structure, conventions, and code templates
  2. Read the java-coding-standard skill for naming, immutability, and style rules
  3. Use Java 21 features: records, sealed interfaces, pattern matching
  4. NEVER call .block() inside a reactive chain
  5. Use Mono.zip() for parallel calls, switchIfEmpty() for not-found
  6. API versioning: /api/v1/...
  7. Use application.yml (not .properties)
  8. Flyway for DB migrations in src/main/resources/db/migration/ (disabled by default; enable with FLYWAY_ENABLED=true)

When Creating a New API

  1. Create the entity and DTO records
  2. Create the R2DBC repository interface
  3. Create the service with reactive logic
  4. Create the controller
  5. Add GlobalExceptionHandler with @ControllerAdvice returning ProblemDetail (RFC 9457)
  6. Add Flyway migration for the DB schema
  7. Write integration tests with @SpringBootTest + WebTestClient
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 46 lines · 0 tokens per session scan A 23a0d7c93a9b

Subscribe to this mod's changes

java-spring-api is an agent published in the GitHub repository kumaran-is/claude-code-onboarding (35 stars, last pushed 2mo ago), licensed MIT. It adds 118 tokens to every session and 601 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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