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auv: Skill for Claude Code

.agents/skills/m13-domain-error/SKILL.md

m13-domain-error is a skill for Claude Code from moeru-ai/auv. It costs 95 tokens per session (1,169 once invoked), scanned A, original, Apache-2.0.

A guide to designing errors for business-domain code. It groups errors by who needs to handle them, whether recovery is possible, and what context is needed for debugging or monitoring.

In plain words
What is it for?
Use it when defining error types, deciding between retrying and failing, adding fallbacks or backoff, writing user-facing messages, or providing debugging and monitoring context.
Why use it?
It helps applications respond appropriately instead of treating user mistakes, temporary network failures, and permanent configuration problems the same way.

Skill for Claude Code

Written for Claude Code: user-invocable in frontmatter. Also seen: installed under .agents/ (shared by several agents).

This is moeru-ai/auv's own configuration. It tells Claude Code how to work on auv itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything auv configures →

not rated 203repo +5 2d ago A scan SkillSpector: pass 95 tokens original Apache-2.0
View source ↗ moeru-ai/auv auv.moeru.ai
Reuse

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.

Copy the file
curl -O https://raw.githubusercontent.com/moeru-ai/auv/main/.agents/skills/m13-domain-error/SKILL.md
Clone the repo
git clone --depth 1 https://github.com/moeru-ai/auv

Made for: Claude Code.

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README.md
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Per session 95 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,169 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00095 $0.01169
Opus 5.5 $0.00038 $0.00468
Sonnet 5.5 $0.00019 $0.00234
Haiku 4.5 $0.00010 $0.00117

Measured 2mo ago against content hash 8b20e875534e, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

m13-domain-error 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.

.agents/skills/m13-domain-error/SKILL.md · 181 lines

How it starts

The opening of the file, as written. The whole thing — 181 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Domain Error Strategy

Layer 2: Design Choices

Core Question

Who needs to handle this error, and how should they recover?

Before designing error types:

  • Is this user-facing or internal?
  • Is recovery possible?
  • What context is needed for debugging?

Error Categorization

Error Type Audience Recovery Example
User-facing End users Guide action InvalidEmail, NotFound
Internal Developers Debug info DatabaseError, ParseError
System Ops/SRE Monitor/alert ConnectionTimeout, RateLimited
Transient Automation Retry NetworkError, ServiceUnavailable
Permanent Human Investigate ConfigInvalid, DataCorrupted

Thinking Prompt

Before designing error types:

  1. Who sees this error?

    • End user → friendly message, actionable
    • Developer → detailed, debuggable
    • Ops → structured, alertable

  2. Can we recover?

    • Transient → retry with backoff
    • Degradable → fallback value
    • Permanent → fail fast, alert

  3. What context is needed?

    • Call chain → anyhow::Context
    • Request ID → structured logging
    • Input data → error payload

Trace Up ↑

To domain constraints (Layer 3):

"How should I handle payment failures?"
    ↑ Ask: What are the business rules for retries?
    ↑ Check: domain-fintech (transaction requirements)
    ↑ Check: SLA (availability requirements)
Question Trace To Ask
Retry policy domain-* What's acceptable latency for retry?
User experience domain-* What message should users see?
Compliance domain-* What must be logged for audit?

Trace Down ↓

To implementation (Layer 1):

"Need typed errors"
    ↓ m06-error-handling: thiserror for library
    ↓ m04-zero-cost: Error enum design

"Need error context"
    ↓ m06-error-handling: anyhow::Context
    ↓ Logging: tracing with fields

"Need retry logic"
    ↓ m07-concurrency: async retry patterns
    ↓ Crates: tokio-retry, backoff

Read the full file on GitHub · 181 lines

Changes

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.

  1. 2mo ago First seen · 181 lines · 95 tokens per session scan A 8b20e875534e

Subscribe to this mod's changes

m13-domain-error is a skill published in the GitHub repository moeru-ai/auv (203 stars, last pushed 2d ago), licensed Apache-2.0. It adds 95 tokens to every session and 1,169 once invoked, about $0.0004 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.

Backend and APIsDebuggingagent-desktopcomputer-usecuagui-automationos-automationphone-use
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