What is async-hygiene?

A C# code checker and fixer for common async/await mistakes, where asynchronous work is started without properly waiting for it or handling cancellation and errors.

Use it to scan a solution for blocking calls, async void methods, missing cancellation tokens, fire-and-forget tasks, unnecessary Task.Run calls, and blocking I/O.

It helps prevent blocked threads, deadlocks, thread-pool exhaustion, unobserved failures, and unreliable background work.

async-hygiene — Skill for Claude Code and Codex by cwoodruff

Install

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.

Any agent

npx skills add cwoodruff/dotnet-claude-code-kit --skill async-hygiene

Clone the repo

git clone --depth 1 https://github.com/cwoodruff/dotnet-claude-code-kit

Made for: Claude Code, Codex.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/cwoodruff/dotnet-claude-code-kit/async-hygiene/github.svg)](https://agentmods.dev/skills/cwoodruff/dotnet-claude-code-kit/async-hygiene)

Your own site

<a href="https://agentmods.dev/skills/cwoodruff/dotnet-claude-code-kit/async-hygiene"><img src="https://agentmods.dev/badge/skills/cwoodruff/dotnet-claude-code-kit/async-hygiene/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/cwoodruff/dotnet-claude-code-kit/async-hygiene"><img src="https://agentmods.dev/badge/skills/cwoodruff/dotnet-claude-code-kit/async-hygiene.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 57 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 389 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.

Origin 100% copy Near-identical to another mod 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.

Model	Per session	Once invoked
Fable 5.1	$0.00057	$0.00389
Opus 5.5	$0.00023	$0.00156
Sonnet 5.5	$0.00011	$0.00078
Haiku 4.5	$0.00006	$0.00039

Measured 1mo ago against content hash 80c2bc150c7a, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

async-hygiene 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 1mo 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.

Origin

This is a copy

100% identical to async-hygiene — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/async-hygiene/SKILL.md · 22 lines

What it actually says

Async/Await Hygiene Sweep

Scan the target scope (default: whole solution) for each anti-pattern, in this order, and fix with the standard remedy:

Anti-pattern	Find	Fix
Sync-over-async	`.Result`, `.Wait()`, `.GetAwaiter().GetResult()`	Make the caller async and await
`async void`	any non-event-handler	Return `Task`
Missing CancellationToken	async public methods without a token parameter	Add `CancellationToken cancellationToken = default` and thread it through
Fire-and-forget	unawaited Task-returning calls	Await, or route through a background service with error handling
`Task.Run` in ASP.NET request path	`Task.Run(` in Api project	Remove — the request is already on a thread-pool thread
Async lambda passed to sync delegate	`async` lambda to `Action<>`	Change delegate type or restructure
Unnecessary `async`/`await` wrapper	method whose only await is the final return	Return the Task directly (unless in a `using`/`try`)
Blocking I/O in async method	`File.ReadAllText`, `Thread.Sleep` inside async	Use async equivalents (`ReadAllTextAsync`, `Task.Delay`)

Process: grep for each pattern → read the surrounding code (some hits are legitimate, e.g. Main, console tools) → fix true positives → dotnet build → report a table of what changed and any hits deliberately left alone with reasoning.

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.

1mo ago First seen · 22 lines · 57 tokens per session scan A 80c2bc150c7a

Subscribe to this mod's changes

async-hygiene is a skill published in the GitHub repository cwoodruff/dotnet-claude-code-kit (2 stars, last pushed 3mo ago), licensed MIT. It adds 57 tokens to every session and 389 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 100% identical to async-hygiene, differing in 0 lines, and is treated as a copy.

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