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.
npx skills add disler/learning-cmux-with-agents --skill cmux-backendgit clone --depth 1 https://github.com/disler/learning-cmux-with-agentsWrote 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.
[](https://agentmods.dev/skills/disler/learning-cmux-with-agents/cmux-backend)<a href="https://agentmods.dev/skills/disler/learning-cmux-with-agents/cmux-backend"><img src="https://agentmods.dev/badge/skills/disler/learning-cmux-with-agents/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.
<a href="https://agentmods.dev/skills/disler/learning-cmux-with-agents/cmux-backend"><img src="https://agentmods.dev/badge/skills/disler/learning-cmux-with-agents/cmux-backend.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
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 21 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.
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 | $0.00053 | $0.00683 |
| Opus 5 | $0.00026 | $0.00342 |
| Sonnet 5 | $0.00011 | $0.00137 |
| Haiku 4.5 | $0.00005 | $0.00068 |
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 11d 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.
How it starts
The opening of the file, as written. The whole thing — 46 lines — stays where its author put it; the contents beside it link to each section on GitHub.
cmux Backend
Use this skill for backend TypeScript, Cloud VM, provider, database, auth, rate-limit, retry, timeout, or telemetry work.
Core rules
- Default backend TypeScript to Effect under
web/app/api/**,web/services/**, and backend scripts that touch providers, databases, auth, rate limits, retries, timeouts, or telemetry. - Keep Next route handlers thin: parse the request, run one Effect program at the boundary, map typed errors to HTTP responses, and treat unexpected defects separately.
- Use plain TypeScript only for trivial data shapes, constants, config files, frontend React code, or small glue where Effect would add ceremony without improving failure handling.
- Cloud VM backend logic must stay in Vercel route handlers and Effect services backed by Postgres.
- Do not reintroduce Rivet or a raw actor protocol for Cloud VM unless a later architecture doc explicitly changes the control plane.
- Production and staging Cloud VM Postgres use the Vercel Marketplace AWS Aurora PostgreSQL OIDC/RDS IAM path.
- Runtime env names are
CMUX_DB_DRIVER=aws-rds-iam,AWS_ROLE_ARN,AWS_REGION,PGHOST,PGPORT,PGUSER, andPGDATABASE. - Run production/staging migrations with
bun db:migrate:aws-rds-iam; never run Drizzle migrations from Vercel build or route startup. - Local development keeps using the
CMUX_PORT-derived Docker Postgres path frombun dev. - Cloud VM create pricing gates should use Stack Auth team payment items when enabled.
- Postgres remains the source of truth for VM lifecycle, active VM limits, idempotency, and usage events.
Secrets
Cloud VM build, test, and local dev scripts use provider secrets from ~/.secrets/cmux.env.
E2B_API_KEYFREESTYLE_API_KEY- R2 upload vars used by
web/scripts/build-cloud-vm-images.tswhen creating Freestyle snapshots
Load them with:
set -a
source ~/.secrets/cmux.env
set +a
~/.secrets/cmuxterm-dev.env is for local Stack/web env and does not contain the provider build keys. bun dev sources ~/.secrets/cmux.env first when present, then ~/.secrets/cmuxterm-dev.env so cmuxterm-specific Stack settings override broader cmux secrets. The web dev loader still accepts the legacy ~/.secret/cmuxterm.env and ~/.secrets/cmuxterm.env paths while machines migrate.
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.
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.
- 11d ago First seen · 46 lines · 53 tokens per session scan A 8d831ad15714
cmux-backend is a skill published in the GitHub repository disler/learning-cmux-with-agents (109 stars, last pushed 2mo ago), licensed MIT. It adds 53 tokens to every session and 683 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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