async-expert

async-expert is a skill for Claude Code, Codex from martinholovsky/claude-skills-generator. It costs 57 tokens per session (4,228 once invoked), scanned A, original, Unlicense.

An expert guide for asynchronous programming, where a program starts work that may finish later without blocking other work. It covers patterns in Python, JavaScript or TypeScript, C#, and Rust.

In plain words
What is it for?
Use it when designing, implementing, reviewing, or optimizing asynchronous code and when checking that language-specific async APIs are correct.
Why use it?
It reduces errors involving event loops, promises, futures, cancellation, failures, and work that runs concurrently.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: model in frontmatter.

Good fit Use it when designing, implementing, reviewing, or optimizing asynchronous code and when checking that language-specific async APIs are correct.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/martinholovsky/claude-skills-generator/async-expert
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 martinholovsky/claude-skills-generator --skill async-expert
Clone the repo
git clone --depth 1 https://github.com/martinholovsky/claude-skills-generator

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.

agentmods badge for async-expert

README.md
[![agentmods](https://agentmods.dev/badge/skills/martinholovsky/claude-skills-generator/async-expert/github.svg)](https://agentmods.dev/skills/martinholovsky/claude-skills-generator/async-expert)
Your own site
<a href="https://agentmods.dev/skills/martinholovsky/claude-skills-generator/async-expert"><img src="https://agentmods.dev/badge/skills/martinholovsky/claude-skills-generator/async-expert/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.

agentmods 80×15 button for async-expert

Your own site · 80×15
<a href="https://agentmods.dev/skills/martinholovsky/claude-skills-generator/async-expert"><img src="https://agentmods.dev/badge/skills/martinholovsky/claude-skills-generator/async-expert.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 4,228 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe.
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 $0.00057 $0.04228
Opus 5 $0.00028 $0.02114
Sonnet 5 $0.00011 $0.00846
Haiku 4.5 $0.00006 $0.00423

Measured 10d ago against content hash 57b09b2c662f, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

async-expert scanned grade A with 1 finding 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 10d 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

grep -r "time\.sleep\|requests\.\|urllib\." src/
skills/async-expert/SKILL.md · 587 lines

How it starts

The opening of the file, as written. The whole thing — 587 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Asynchronous Programming Expert

0. Anti-Hallucination Protocol

🚨 MANDATORY: Read before implementing any code using this skill

Verification Requirements

When using this skill to implement async features, you MUST:

  1. Verify Before Implementing

    • ✅ Check official documentation for async APIs (asyncio, Node.js, C# Task)
    • ✅ Confirm method signatures match target language version
    • ✅ Validate async patterns are current (not deprecated)
    • ❌ Never guess event loop methods or task APIs
    • ❌ Never invent promise/future combinators
    • ❌ Never assume async API behavior across languages
  2. Use Available Tools

    • 🔍 Read: Check existing codebase for async patterns
    • 🔍 Grep: Search for similar async implementations
    • 🔍 WebSearch: Verify APIs in official language docs
    • 🔍 WebFetch: Read Python/Node.js/C# async documentation
  3. Verify if Certainty < 80%

    • If uncertain about ANY async API/method/pattern
    • STOP and verify before implementing
    • Document verification source in response
    • Async bugs are hard to debug - verify first
  4. Common Async Hallucination Traps (AVOID)

    • ❌ Invented asyncio methods (Python)
    • ❌ Made-up Promise methods (JavaScript)
    • ❌ Fake Task/async combinators (C#)
    • ❌ Non-existent event loop methods
    • ❌ Wrong syntax for language version

Self-Check Checklist

Before EVERY response with async code:

  • All async imports verified (asyncio, concurrent.futures, etc.)
  • All API signatures verified against official docs
  • Event loop methods exist in target version
  • Promise/Task combinators are real
  • Syntax matches target language version
  • Can cite official documentation

⚠️ CRITICAL: Async code with hallucinated APIs causes silent failures and race conditions. Always verify.


1. Core Principles

  1. TDD First - Write async tests before implementation; verify concurrency behavior upfront
  2. Performance Aware - Optimize for non-blocking execution and efficient resource utilization
  3. Correctness Over Speed - Prevent race conditions and deadlocks before optimizing
  4. Resource Safety - Always clean up connections, handles, and tasks
  5. Explicit Error Handling - Handle async errors at every level

Read the full file on GitHub · 587 lines

Files

What ships with it

3 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.

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. 10d ago First seen · 587 lines · 57 tokens per session scan A 57b09b2c662f

Subscribe to this mod's changes

async-expert is a skill published in the GitHub repository martinholovsky/claude-skills-generator (45 stars, last pushed 9mo ago), licensed Unlicense. It adds 57 tokens to every session and 4,228 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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