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/jabrena/plinth/121-java-object-oriented-designnpx skills add jabrena/plinth --skill 121-java-object-oriented-designgit clone --depth 1 https://github.com/jabrena/plinthWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/jabrena/plinth/121-java-object-oriented-design)<a href="https://agentmods.dev/skills/jabrena/plinth/121-java-object-oriented-design"><img src="https://agentmods.dev/badge/skills/jabrena/plinth/121-java-object-oriented-design.svg" alt="Measured on agentmods" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00107 | $0.01746 |
| Opus 5 | $0.00053 | $0.00873 |
| Sonnet 5 | $0.00021 | $0.00349 |
| Haiku 4.5 | $0.00011 | $0.00175 |
Grade A, and why
121-java-object-oriented-design 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 — 127 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Java Object-Oriented Design Guidelines
Review and improve Java code using focused object-oriented design references selected after assessing the request and affected code.
What is covered in this Skill?
- Fundamental design principles (SOLID, DRY, YAGNI)
- Class and interface design: composition over inheritance, immutability, accessibility minimization, accessor methods
- Core OOP concepts: encapsulation, inheritance, polymorphism
- Object creation patterns: static factory methods, Builder, Singleton, dependency injection, avoiding unnecessary objects
- OOD code smells: God Class, Feature Envy, Inappropriate Intimacy, Refused Bequest, Shotgun Surgery, Data Clumps
- Method design: parameter validation, defensive copies, careful signatures, empty collections over nulls, Optional usage
- Exception handling: checked vs. runtime exceptions, standard exceptions, failure-capture messages, no silent ignoring
Scope: Classify the applicable OOD concerns first, then load only the focused references needed for those concerns. Load multiple references when a refactoring crosses concern boundaries.
Constraints
Before applying any OOD changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until resolved. After applying improvements, run full verification.
- MANDATORY: Run
./mvnw compileormvn compilebefore applying any change - SAFETY: If compilation fails, stop immediately and do not proceed — compilation failure is a blocking condition
- VERIFY: Run
./mvnw clean verifyormvn clean verifyafter applying improvements - PROGRESSIVE DISCLOSURE: Classify the applicable OOD concerns before reading references, then read only the references mapped to those concerns
- MULTI-CONCERN CHANGES: Read multiple focused references only when the request or diagnosed code problems cross concern boundaries
- PRESERVE BEHAVIOR: Apply focused, incremental refactorings without changing observable business behavior
- INCREMENTAL SAFETY: Compile after each significant refactoring and keep changes easy to revert if validation reveals a regression
- DEPENDENCY SAFETY: Confirm refactoring does not break imports, dependencies, class relationships, or established contracts
- ADJACENT SKILLS: Use skill 122 for dedicated type-design work and skill 126 for dedicated exception-handling work; use the overlapping skill 121 references only when those topics are part of a broader OOD review
- EDGE CASE: If request scope is ambiguous, stop and ask a clarifying question before applying changes
- EDGE CASE: If required inputs, files, or tooling are missing, report what is missing and ask whether to proceed with setup guidance
What ships with it
8 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.
- references/121-java-object-oriented-design-classes-interfaces.md 10 KB
- references/121-java-object-oriented-design-code-smells.md 6.5 KB
- references/121-java-object-oriented-design-enums-annotations.md 8.8 KB
- references/121-java-object-oriented-design-exceptions.md 13 KB
- references/121-java-object-oriented-design-methods.md 12 KB
- references/121-java-object-oriented-design-object-creation.md 10.0 KB
- references/121-java-object-oriented-design-oop-concepts.md 8.2 KB
- references/121-java-object-oriented-design-principles.md 16 KB
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 · 127 lines · 107 tokens per session scan A dc727522f1cb
121-java-object-oriented-design is a skill published in the GitHub repository jabrena/plinth (435 stars, last pushed today), licensed Apache-2.0. It adds 107 tokens to every session and 1,746 once invoked, about $0.0005 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 2026-09-03.
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