cmux-backend

cmux-backend is a skill for Codex from manaflow-ai/cmux. It costs 53 tokens per session (612 once invoked), scanned A, original, no licence file.

A set of project rules for developing cmux's TypeScript backend, web app, services, scripts, and cloud virtual machines. It also covers provider integrations, PostgreSQL, billing checks, database changes, and machine-image build scripts.

In plain words
What is it for?
Use it while editing backend or web code, managing cloud virtual machines, changing database migrations, integrating providers, or working on Stack Auth pricing gates and image builds.
Why use it?
It gives coding agents the project-specific guidance needed when changing backend code or cloud infrastructure.

Skill for Codex

Written for Codex: agents/openai.yaml present.

Good fit Use it while editing backend or web code, managing cloud virtual machines, changing database migrations, integrating providers, or working on Stack Auth pricing gates and image builds.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/manaflow-ai/cmux/cmux-backend
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 manaflow-ai/cmux --skill cmux-backend
Clone the repo
git clone --depth 1 https://github.com/manaflow-ai/cmux

Made for: 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 cmux-backend

README.md
[![agentmods](https://agentmods.dev/badge/skills/manaflow-ai/cmux/cmux-backend/github.svg)](https://agentmods.dev/skills/manaflow-ai/cmux/cmux-backend)
Your own site
<a href="https://agentmods.dev/skills/manaflow-ai/cmux/cmux-backend"><img src="https://agentmods.dev/badge/skills/manaflow-ai/cmux/cmux-backend/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 cmux-backend

Your own site · 80×15
<a href="https://agentmods.dev/skills/manaflow-ai/cmux/cmux-backend"><img src="https://agentmods.dev/badge/skills/manaflow-ai/cmux/cmux-backend.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 53 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 612 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
  • Socket pass 2 Sept 2026
  • Snyk pass 2 Sept 2026
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 1 finding, up to medium

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • medium Rogue Agent · line 17
    Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.
    Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
How audits are shown
Origin unknown 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 $0.00053 $0.00612
Opus 5 $0.00026 $0.00306
Sonnet 5 $0.00011 $0.00122
Haiku 4.5 $0.00005 $0.00061

Measured 6d ago against content hash 8646f7ba3365, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

cmux-backend 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 6d 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.

skills/cmux-backend/SKILL.md · 35 lines

The source is not reproduced here

A licence we could not identify

The repository carries a LICENSE file, but it is custom or dual enough that GitHub cannot name it and neither can this catalogue. Unknown terms are not permission, so the body is not copied here. Read the licence at the source and decide for yourself.

Read it on GitHub

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. 6d ago Changed 8646f7ba3365
  2. 10d ago First seen · 35 lines · 53 tokens per session scan A 8fdac186e94e

Subscribe to this mod's changes

cmux-backend is a skill published in the GitHub repository manaflow-ai/cmux (26,926 stars, last pushed yesterday), with no licence file. It adds 53 tokens to every session and 612 once invoked, about $0.0003 per session on Opus 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.

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