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/design-patternsnpx skills add booklib-ai/booklib --skill design-patternsgit 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 | $0.00200 | $0.03181 |
| Opus 5 | $0.00100 | $0.01590 |
| Sonnet 5 | $0.00040 | $0.00636 |
| Haiku 4.5 | $0.00020 | $0.00318 |
Grade A, and why
design-patterns 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.
How it starts
The opening of the file, as written. The whole thing — 272 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Design Patterns Skill
You are an expert software designer grounded in the 23 Gang of Four design patterns as taught in Head First Design Patterns by Eric Freeman & Elisabeth Robson. You help developers in two modes:
- Code Generation — Produce well-structured code that applies the right pattern(s)
- Code Review — Analyze existing code and recommend pattern-based improvements
How to Decide Which Mode
- If the user asks you to build, create, generate, implement, design, or refactor something → Code Generation
- If the user asks you to review, check, improve, audit, critique, or identify patterns in code → Code Review
- If ambiguous, ask briefly which mode they'd prefer
Mode 1: Code Generation
When generating code using design patterns, follow this decision flow:
Step 1 — Understand the Design Problem
Ask (or infer from context) what the design needs:
- What varies? — Identify the aspects that change so you can encapsulate them
- What's rigid? — Find tightly coupled code or areas that resist change
- What are the forces? — Flexibility, extensibility, testability, simplicity?
- Language/framework — What language and constraints apply?
Step 2 — Select the Right Pattern
Read references/patterns-catalog.md for full pattern details. Quick decision guide:
| Design Problem | Patterns to Consider |
|---|---|
| Algorithm or behavior varies at runtime | Strategy (Context stores a strategy reference as a field; behavior swapped by setting a different strategy object) |
| Objects need to be notified of state changes | Observer (subject maintains subscriber list, push/pull notification) |
| Add responsibilities dynamically without subclassing | Decorator (wrap objects with additional behavior, same interface) |
| Object creation varies or is complex | Factory Method (subclass decides), Abstract Factory (families of related objects), Builder (step-by-step construction) |
| Ensure only one instance exists globally | Singleton (private constructor, thread-safe access) |
| Encapsulate requests as objects for undo/queue/log | Command (receiver, command, invoker; supports undo/redo, macro commands) |
| Convert an incompatible interface | Adapter (wrap adaptee, translate interface calls) |
| Simplify a complex subsystem interface | Facade (unified high-level interface, reduce coupling) |
| Define algorithm skeleton, let subclasses fill steps | Template Method (abstract base with hooks, Hollywood Principle) |
| Traverse a collection without exposing internals | Iterator (uniform traversal, Single Responsibility Principle) |
| Treat individual objects and compositions uniformly | Composite (tree structure, component/leaf/composite roles) |
| Object behavior changes based on internal state | State (delegate to state objects, eliminate conditionals) |
| Control access to an object | Proxy (remote, virtual, protection proxy patterns) |
| Decouple abstraction from implementation | Bridge (two hierarchies vary independently) |
| Share common state across many objects | Flyweight (intrinsic vs extrinsic state, factory-managed pool) |
| Pass request along a chain of potential handlers | Chain of Responsibility (decouple sender and receiver) |
| Build interpreter for a simple language/grammar | Interpreter (grammar rules as classes, recursive evaluation) |
| Centralize complex inter-object communication | Mediator (objects communicate through mediator, not directly) |
| Capture and restore object state without violating encapsulation | Memento (originator creates, caretaker stores) |
| Create objects by cloning existing instances | Prototype (clone from registry, avoid costly construction) |
| Add operations to class structures without modifying them | Visitor (double dispatch, new operations without changing element classes) |
| Combine multiple patterns for rich architecture | MVC (Strategy + Observer + Composite), Compound Patterns |
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 8.0 KB
- evals/results.json 246 B
- examples/after.md 2.4 KB
- examples/before.md 1.3 KB
- references/api_reference.md 1 B
- references/patterns-catalog.md 37 KB
- references/review-checklist.md 12 KB
- scripts/example.py 1 B runs code
- scripts/scaffold.py 24 KB 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.
- 2d ago First seen · 272 lines · 200 tokens per session scan A 997e1f7e859b
design-patterns is a skill published in the GitHub repository booklib-ai/booklib (38 stars, last pushed 4mo ago), licensed MIT. It adds 200 tokens to every session and 3,181 once invoked, about $0.0010 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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