healthcheck

A guide for checking and hardening the computer that runs Understudy, an agent deployment. It covers access, network exposure, firewall, SSH, backups, and operating-system updates.

In plain words
What is it for?
Use it to review a host, inspect open network services and remote access, assess firewall and update settings, and plan recurring security checks.
Why use it?
It helps identify security risks before changing the machine. It also keeps host security settings separate from the agent's own configuration and requires approval before changes.

Skill for Claude CodeCodex

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.

agentmods
npx agentmods add skills/understudy-ai/understudy/healthcheck
Any agent
npx skills add understudy-ai/understudy --skill healthcheck
Clone the repo
git clone --depth 1 https://github.com/understudy-ai/understudy

Made for: Claude Code, Codex.

Per session 46 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,106 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00046 $0.01106
Opus 5 $0.00023 $0.00553
Sonnet 5 $0.00009 $0.00221
Haiku 4.5 $0.00005 $0.00111

Measured 3d ago against content hash f87a151fda6e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

healthcheck 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 3d 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/healthcheck/SKILL.md · 145 lines

How it starts

The opening of the file, as written. The whole thing — 145 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Understudy Host Hardening

Overview

Assess the host that runs Understudy, keep host controls separate from Understudy configuration, and require explicit approval before any change.

Core Rules

  • Start with read-only checks.
  • Require explicit approval before any state-changing action.
  • Do not modify remote access settings until the current access path is confirmed.
  • Prefer reversible changes with a rollback plan.
  • Never claim Understudy itself changes the host firewall, SSH policy, or OS update settings.
  • If identity or role is unclear, provide recommendations only.
  • Present user choices as numbered lists.

Read-Only Workflow

  1. Establish context:
    • OS and version
    • local console vs SSH/RDP/tunnel/tailnet access
    • admin/root availability
    • public exposure, reverse proxy, or private-only reachability
    • backups, disk encryption, and automatic security updates
  2. Run host checks:
    • uname -a, sw_vers, cat /etc/os-release
    • Linux: ss -ltnup, ufw status, firewall-cmd --state, nft list ruleset
    • macOS: lsof -nP -iTCP -sTCP:LISTEN, /usr/libexec/ApplicationFirewall/socketfilterfw --getglobalstate, pfctl -s info
    • macOS backups: tmutil status
  3. Run Understudy checks:
    • understudy security --audit
    • understudy status --json
    • understudy health --json
    • understudy logs --tail 100
    • understudy doctor --deep when broader local diagnostics are needed

Ask once for permission to run read-only checks. If granted, infer as much as possible from commands before asking follow-up questions.

Risk Profiles

Offer one of these numbered defaults after the host context is known:

  1. Home / workstation balanced
  2. Remote / headless hardened
  3. Developer convenience with explicit exposure warnings
  4. Custom constraints supplied by the user

Remediation Plan

Always present the plan before making changes. Include:

  • target profile
  • current posture summary
  • gaps vs target
  • exact commands to run
  • rollback or access-preservation notes
  • credential and file-permission hygiene notes

Read the full file on GitHub · 145 lines

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. 3d ago First seen · 145 lines · 46 tokens per session scan A f87a151fda6e

Subscribe to this mod's changes

healthcheck is a skill published in the GitHub repository understudy-ai/understudy (456 stars, last pushed 2mo ago), licensed MIT. It adds 46 tokens to every session and 1,106 once invoked, about $0.0002 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.