What is netcat-async?

A manager for persistent two-way TCP connections, the network links used by tools such as netcat, with background reading and writing.

Use it to start or listen for connections, send payloads, read responses, inspect session status, and stop reusable sessions during protocol testing or CTF work.

It keeps a connection open across multiple messages and preserves session status and logs.

netcat-async — Skill for Claude Code and Codex by 02loveslollipop

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 02loveslollipop/OpenCROW --skill netcat-async

Clone the repo

git clone --depth 1 https://github.com/02loveslollipop/OpenCROW

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/02loveslollipop/opencrow/netcat-async/github.svg)](https://agentmods.dev/skills/02loveslollipop/opencrow/netcat-async)

Your own site

<a href="https://agentmods.dev/skills/02loveslollipop/opencrow/netcat-async"><img src="https://agentmods.dev/badge/skills/02loveslollipop/opencrow/netcat-async/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/02loveslollipop/opencrow/netcat-async"><img src="https://agentmods.dev/badge/skills/02loveslollipop/opencrow/netcat-async.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 67 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 755 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.

Model	Per session	Once invoked
Fable 5.1	$0.00067	$0.00755
Opus 5.5	$0.00027	$0.00302
Sonnet 5.5	$0.00013	$0.00151
Haiku 4.5	$0.00007	$0.00076

Measured 1mo ago against content hash 087324c46850, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

netcat-async 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.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/nc_async_session.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

skills/netcat-async/SKILL.md · 85 lines

How it starts

The opening of the file, as written. The whole thing — 85 lines — stays where its author put it; the contents beside it link to each section on GitHub.

OpenCROW I/O - Netcat Async

Runtime preflight

Probe required commands with command -v and Python modules with importlib.util.find_spec before use. Prefer a PATH-resolved OpenCROW MCP helper or the ctf/sage environment when available, then the managed helper or system Python. If a capability is missing, stop that path safely and report the exact missing command or module.

Prefer the opencrow-netcat-mcp server for session lifecycle, reads, and writes. Fall back to scripts/ncx only when you need to inspect or debug the backend directly.

MCP First

Use toolbox_info, toolbox_verify, and toolbox_capabilities first.
Use the generic session tools:
- session_start
- session_listen
- session_send
- session_read
- session_status
- session_stop
Keep one named session per target flow so the MCP server can report stable artifacts under /tmp/opencrow-nc-async/<name>/.

Use scripts/ncx to manage long-lived TCP sessions instead of one-shot nc invocations when you are operating outside MCP.

Workflow

Start a named outbound session, or listen for one inbound connection.
Send one or more payloads while the daemon keeps receiving output asynchronously.
Read logs (tail for recent data, follow for streaming).
Stop the session when done.

Commands

# Start session
scripts/ncx start --name demo --host 127.0.0.1 --port 9001

# Listen on loopback for one inbound connection (port 0 selects a free port)
scripts/ncx listen --name inbound --port 0

# Send text (append newline for line-oriented protocols)
scripts/ncx send --name demo --data 'ping' --newline

# Send exact bytes using hex or strict base64
scripts/ncx send --name demo --hex '00 03 ff'

# Read latest output
scripts/ncx read --name demo --tail 40

# Follow output live
scripts/ncx read --name demo --follow

# Check metadata and process state
scripts/ncx status --name demo

# Stop session
scripts/ncx stop --name demo

Operational Rules

Read the full file on GitHub · 85 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.

1mo ago First seen · 85 lines · 67 tokens per session scan A 087324c46850

Subscribe to this mod's changes

netcat-async is a skill published in the GitHub repository 02loveslollipop/OpenCROW (10 stars, last pushed yesterday), licensed Apache-2.0. It adds 67 tokens to every session and 755 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 2026-08-31.

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Authorized web security reference for selecting attack categories, payload families, bypass notes, workflow summaries, and mitigations across web, API, JWT, cloud, AI, framework, and WebSocket testing. Use for pentest planning, report drafting, or converting the extracted wiki into narrower web-focused skills.

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netcat-async