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/fellipeutaka/leon/design-patternsnpx skills add fellipeutaka/leon --skill design-patternsgit clone --depth 1 https://github.com/fellipeutaka/leonWrote 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/fellipeutaka/leon/design-patterns)<a href="https://agentmods.dev/skills/fellipeutaka/leon/design-patterns"><img src="https://agentmods.dev/badge/skills/fellipeutaka/leon/design-patterns.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 | $0.00114 | $0.01260 |
| Opus 5 | $0.00057 | $0.00630 |
| Sonnet 5 | $0.00023 | $0.00252 |
| Haiku 4.5 | $0.00011 | $0.00126 |
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 3d 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 — 136 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Design Patterns
Proven architectural patterns for building maintainable, extensible, and testable TypeScript codebases. All 22 Gang of Four patterns with practical implementations.
When to Apply
Reference these patterns when:
- Solving recurring architectural problems
- Refactoring tightly coupled code
- Building plugin/extension systems
- Making code more testable via dependency injection
- Reviewing PRs with architectural concerns
- Choosing between inheritance and composition
Pattern Categories
Creational Patterns
Create objects flexibly, hiding creation logic from consumers.
| Pattern | Intent |
|---|---|
| Factory Method | Delegate object creation to subclasses |
| Abstract Factory | Create families of related objects without concrete types |
| Builder | Construct complex objects step-by-step |
| Prototype | Clone existing objects instead of building from scratch |
| Singleton | Ensure exactly one instance with global access |
See references/CREATIONAL.md for implementations.
Structural Patterns
Compose classes and objects into larger, flexible structures.
| Pattern | Intent |
|---|---|
| Adapter | Make incompatible interfaces work together |
| Bridge | Separate abstraction from implementation |
| Composite | Treat individual objects and compositions uniformly |
| Decorator | Attach responsibilities dynamically without subclassing |
| Facade | Simplify complex subsystem with a unified interface |
| Flyweight | Share common state to reduce memory across many objects |
| Proxy | Control access to an object through a substitute |
What ships with it
4 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.
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.
- 3d ago First seen · 136 lines · 114 tokens per session scan A 0b5b96e9adbb
design-patterns is a skill published in the GitHub repository fellipeutaka/leon (5 stars, last pushed 5d ago), licensed MIT. It adds 114 tokens to every session and 1,260 once invoked, about $0.0006 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 2026-08-31.
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