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 skills add mickeyyaya/refactoring-skills --skill type-system-patternsgit clone --depth 1 https://github.com/mickeyyaya/refactoring-skillsWrote 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/mickeyyaya/refactoring-skills/type-system-patterns)<a href="https://agentmods.dev/skills/mickeyyaya/refactoring-skills/type-system-patterns"><img src="https://agentmods.dev/badge/skills/mickeyyaya/refactoring-skills/type-system-patterns/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/mickeyyaya/refactoring-skills/type-system-patterns"><img src="https://agentmods.dev/badge/skills/mickeyyaya/refactoring-skills/type-system-patterns.svg" alt="Reviewed on agentmods" width="80" 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 5.1 | $0.00077 | $0.02906 |
| Opus 5 | $0.00039 | $0.01453 |
| Sonnet 5 | $0.00015 | $0.00581 |
| Haiku 4.5 | $0.00008 | $0.00291 |
Grade A, and why
type-system-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 9d 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 — 318 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Type System Patterns for Code Review
Overview
A strong type system is the first line of defense against bugs. When used well, types make illegal states unrepresentable — the compiler catches entire classes of errors before any test runs.
When to Use
- APIs accepting raw strings where a typed value is expected
- Functions returning
null/undefinedor throwing where a Result type belongs - Codebases with frequent
anycasts or type assertions - State machines implemented as ad-hoc string/boolean flags
- Runtime validation that could be moved to compile time
Quick Reference
| Pattern | Core Idea | Primary Red Flag |
|---|---|---|
| Discriminated Unions | Tag each variant; switch exhaustively | instanceof chains, stringly-typed variants |
| Phantom Types | Compile-time info with no runtime cost | Mixing validated/unvalidated data of same shape |
| Branded/Nominal Types | Structurally identical types made distinct | Passing userId where orderId required |
| Generic Constraints | Bound type params to enforce contracts | any escape hatches, unconstrained generics |
| Type Narrowing / Guards | Runtime checks informing the type system | Unsafe as casts, as unknown as T |
| Immutable Types | readonly and const at the type level |
Mutable types on value objects and DTOs |
| Newtype Pattern | Wrap primitives for semantic safety | Raw strings for emails, IDs, URLs |
| Result / Option Types | Type-safe absence and error handling | null returns, exception-based control flow |
| Builder with Types | Compile-time required-field enforcement | Runtime errors from incomplete builders |
| Conditional Types | Type-level computation and inference | Untyped overloads, duplicated type logic |
Patterns in Detail
1. Discriminated Unions / Tagged Unions
Represent a fixed set of mutually exclusive variants with a literal discriminant tag. Compiler enforces exhaustive handling and narrows types per branch.
Red Flags: instanceof chains or parallel boolean flags allowing impossible combinations; type/status typed as string instead of literal union; switch with no exhaustiveness guard.
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.
- 9d ago First seen · 318 lines · 77 tokens per session scan A 28b714fc81df
type-system-patterns is a skill published in the GitHub repository mickeyyaya/refactoring-skills (6 stars, last pushed 5mo ago), licensed MIT. It adds 77 tokens to every session and 2,906 once invoked, about $0.0004 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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