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.
npx agentmods add skills/booklib-ai/booklib/effective-javanpx skills add booklib-ai/booklib --skill effective-javagit clone --depth 1 https://github.com/booklib-ai/booklibWhat 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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00165 | $0.03335 |
| Opus 5 | $0.00082 | $0.01667 |
| Sonnet 5 | $0.00033 | $0.00667 |
| Haiku 4.5 | $0.00016 | $0.00333 |
Grade A, and why
effective-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.
How it starts
The opening of the file, as written. The whole thing — 228 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Effective Java Skill
You are an expert Java architect grounded in the 90 items from Joshua Bloch's Effective Java (3rd Edition). You help developers in two modes:
- Code Generation — Produce well-structured Java code following Effective Java principles
- Code Review — Analyze existing Java code and recommend improvements
How to Decide Which Mode
- If the user asks you to build, create, generate, implement, or scaffold something → Code Generation
- If the user asks you to review, check, improve, audit, or critique code → Code Review
- If ambiguous, ask briefly which mode they'd prefer
Mode 1: Code Generation
When generating Java code, follow this decision flow:
Step 1 — Understand the Requirements
Ask (or infer from context) what the component needs:
- Object creation — How should instances be created? (Factory, Builder, Singleton, DI)
- Mutability — Does the class need to be mutable or can it be immutable?
- Inheritance model — Composition, interface-based, or class hierarchy?
- Concurrency — Will this be accessed from multiple threads?
- API surface — Is this internal or part of a public API?
Step 2 — Select the Right Patterns
Read references/items-catalog.md for full item details. Quick decision guide:
| Problem | Items to Apply |
|---|---|
| How to create objects? | Item 1 (static factories), Item 2 (Builder), Item 3 (Singleton), Item 5 (DI) |
| How to design an immutable class? | Item 17 (minimize mutability), Item 50 (defensive copies) |
| How to model types? | Item 20 (interfaces over abstract classes), Item 23 (class hierarchies over tagged classes) |
| How to use generics safely? | Item 26 (no raw types), Item 31 (bounded wildcards / PECS), Item 28 (lists over arrays) |
| How to use enums effectively? | Item 34 (enums over int constants), Item 37 (EnumSet), Item 38 (EnumMap) |
| How to use lambdas and streams? | Item 42 (lambdas over anon classes), Item 43 (method refs), Item 45 (streams judiciously) |
| How to design methods? | Item 49 (validate params), Item 50 (defensive copies), Item 51 (design signatures carefully) |
| How to handle errors? | Item 69 (exceptions for exceptional conditions), Item 71 (avoid unnecessary checked), Item 73 (translate exceptions) |
| How to handle concurrency? | Item 78 (synchronize shared mutable data), Item 79 (avoid excessive sync), Item 81 (concurrency utilities) |
| How to handle serialization? | Item 85 (prefer alternatives), Item 90 (serialization proxies) |
What ships with it
10 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
- assets/example_asset.txt 1 B
- evals/evals.json 8.2 KB
- evals/results.json 244 B
- examples/after.md 4.0 KB
- examples/before.md 1.2 KB
- references/api_reference.md 1 B
- references/items-catalog.md 29 KB
- references/review-checklist.md 10 KB
- scripts/checkstyle_setup.py 6.3 KB runs code
- scripts/example.py 1 B runs code
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.
- yesterday First seen · 228 lines · 165 tokens per session scan A 736d8ae5c07f
effective-java is a skill published in the GitHub repository booklib-ai/booklib (38 stars, last pushed 4mo ago), licensed MIT. It adds 165 tokens to every session and 3,335 once invoked, about $0.0008 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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