java-21-development-standards

A set of coding rules for Java 21, a long-term-support version of Java. It draws on Effective Java, Google's Java style guidance, and current Java 21 practices.

In plain words
What is it for?
Use it when building or reviewing Java 21 applications, libraries, and services, especially when setting team coding standards.
Why use it?
It gives Java developers consistent guidance for writing and reviewing code without having to remember several style and design references.

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/beettlle/cursorrules/java-21-development-standards
Clone the repo
git clone --depth 1 https://github.com/beettlle/CursorRules

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 10,694 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin unknown 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 $0.10694
Opus 5 $0.00000 $0.05347
Sonnet 5 $0.00000 $0.02139
Haiku 4.5 $0.00000 $0.01069

Measured yesterday against content hash a464195155ed, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

java-21-development-standards 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-21-development-standards.mdc · 736 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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 · 736 lines · 0 tokens per session scan A a464195155ed

Subscribe to this mod's changes

java-21-development-standards is a cursor rule published in the GitHub repository beettlle/CursorRules (2 stars, last pushed 17d ago), with no licence file. It costs nothing until one of its globs matches a file; then it loads 10,694 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 2026-08-31.