java

A set of Java development rules for Klag, a Kafka consumer-lag monitoring service. It covers asynchronous Vert.x code, Java 21 records, configuration, logging, tests, and read-only Kafka access.

In plain words
What is it for?
Use it when editing Java source or tests, reading configuration, changing Kafka clients, or preparing a Klag pull request.
Why use it?
It keeps changes consistent with the project’s non-blocking design and clarifies how to test Kafka and metrics behavior safely.

Cursor rule for Cursor

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 rules/themoah/klag/java
Clone the repo
git clone --depth 1 https://github.com/themoah/klag

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 240 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 $0.00000 $0.00240
Opus 5 $0.00000 $0.00120
Sonnet 5 $0.00000 $0.00048
Haiku 4.5 $0.00000 $0.00024

Measured yesterday against content hash 664f49501059, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

java 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 yesterday.

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.

.cursor/rules/java.mdc · 25 lines

What it actually says

Java conventions

  • Non-blocking only: Kafka/HTTP work via Vert.x Future<T>; no blocking calls on event loops
  • Model types are Java 21 records under model/
  • Config via Env.resolve() — env var → -DNAME-Dname.dotted (env wins)
  • Logging: SLF4J; package loggers follow existing logback.xml levels (LOG_LEVEL_* env vars)

Testing

  • Unit tests mirror package layout under src/test/java/
  • Run ./gradlew test before PRs; add tests for non-trivial metric or Kafka client behavior
  • Do not add tests that only assert obvious behavior

Kafka client notes

  • AdminClient only; read-only DESCRIBE ACLs (cluster, topic *, group *)
  • Request batching: KAFKA_CHUNK_COUNT, KAFKA_CHUNK_DELAY_MS
  • Kafka 2.x: MAX_TIMESTAMP listOffsets unsupported — falls back to LATEST (expected WARN once per process)
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. yesterday First seen · 25 lines · 0 tokens per session scan A 664f49501059

Subscribe to this mod's changes

java is a cursor rule published in the GitHub repository themoah/klag (81 stars, last pushed yesterday), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 240 tokens. 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.