Borrowing it
Nothing to install: this file belongs to moeru-ai/auv. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/moeru-ai/auv/main/.agents/skills/m04-zero-cost/SKILL.mdgit clone --depth 1 https://github.com/moeru-ai/auvWrote 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/moeru-ai/auv/m04-zero-cost)<a href="https://agentmods.dev/skills/moeru-ai/auv/m04-zero-cost"><img src="https://agentmods.dev/badge/skills/moeru-ai/auv/m04-zero-cost/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/moeru-ai/auv/m04-zero-cost"><img src="https://agentmods.dev/badge/skills/moeru-ai/auv/m04-zero-cost.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00078 | $0.01141 |
| Opus 5.5 | $0.00031 | $0.00456 |
| Sonnet 5.5 | $0.00016 | $0.00228 |
| Haiku 4.5 | $0.00008 | $0.00114 |
Grade A, and why
m04-zero-cost 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 2mo 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 — 166 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Zero-Cost Abstraction
Layer 1: Language Mechanics
Core Question
Do we need compile-time or runtime polymorphism?
Before choosing between generics and trait objects:
- Is the type known at compile time?
- Is a heterogeneous collection needed?
- What's the performance priority?
Error → Design Question
| Error | Don't Just Say | Ask Instead |
|---|---|---|
| E0277 | "Add trait bound" | Is this abstraction at the right level? |
| E0308 | "Fix the type" | Should types be unified or distinct? |
| E0599 | "Import the trait" | Is the trait the right abstraction? |
| E0038 | "Make object-safe" | Do we really need dynamic dispatch? |
Thinking Prompt
Before adding trait bounds:
-
What abstraction is needed?
- Same behavior, different types → trait
- Different behavior, same type → enum
- No abstraction needed → concrete type
-
When is type known?
- Compile time → generics (static dispatch)
- Runtime → trait objects (dynamic dispatch)
-
What's the trade-off priority?
- Performance → generics
- Compile time → trait objects
- Flexibility → depends
Trace Up ↑
When type system fights back:
E0277 (trait bound not satisfied)
↑ Ask: Is the abstraction level correct?
↑ Check: m09-domain (what behavior is being abstracted?)
↑ Check: m05-type-driven (should use newtype?)
| Persistent Error | Trace To | Question |
|---|---|---|
| Complex trait bounds | m09-domain | Is the abstraction right? |
| Object safety issues | m05-type-driven | Can typestate help? |
| Type explosion | m10-performance | Accept dyn overhead? |
Trace Down ↓
From design to implementation:
"Need to abstract over types with same behavior"
↓ Types known at compile time → impl Trait or generics
↓ Types determined at runtime → dyn Trait
"Need collection of different types"
↓ Closed set → enum
↓ Open set → Vec<Box<dyn Trait>>
"Need to return different types"
↓ Same type → impl Trait
↓ Different types → Box<dyn Trait>
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.
- 2mo ago First seen · 166 lines · 78 tokens per session scan A 3a2eed8faf0a
m04-zero-cost is a skill published in the GitHub repository moeru-ai/auv (203 stars, last pushed 2d ago), licensed Apache-2.0. It adds 78 tokens to every session and 1,141 once invoked, about $0.0003 per session on Opus 5.5. 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.
m04-zero-cost compared with skills from other repositories
| Mod | Type | Stars | Last push | Licence | Scan | Tokens | Works with |
|---|---|---|---|---|---|---|---|
| m04-zero-costmoeru-ai/auv | Skill | 203 | 2d ago | Apache-2.0 | A | 78 | Claude Code |
| rust-patternsaffaan-m/ECC | Skill | 298k | 4d ago | MIT | A | 28 | Claude Code, Kiro |
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