goodskill

goodskill is a skill for Claude Code, Codex from haabe/mycelium. It costs 23 tokens per session (124 once invoked), scanned A, original, MIT.

A development procedure for updating a project canvas after first reading the file that will change.

In plain words
What is it for?
Safely updating the project purpose canvas.
Why use it?
It reduces the risk of overwriting project information without checking its current contents.

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/haabe/mycelium/goodskill
Any agent
npx skills add haabe/mycelium --skill goodskill
Clone the repo
git clone --depth 1 https://github.com/haabe/mycelium

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 goodskill

README.md
[![agentmods](https://agentmods.dev/badge/skills/haabe/mycelium/goodskill.svg)](https://agentmods.dev/skills/haabe/mycelium/goodskill)
Your own site
<a href="https://agentmods.dev/skills/haabe/mycelium/goodskill"><img src="https://agentmods.dev/badge/skills/haabe/mycelium/goodskill.svg" alt="Measured on agentmods" height="20"></a>
Per session 23 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 124 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 $0.00023 $0.00124
Opus 5 $0.00012 $0.00062
Sonnet 5 $0.00005 $0.00025
Haiku 4.5 $0.00002 $0.00012

Measured yesterday against content hash 0d73eaf20d6f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

goodskill 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 yesterday.

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.

tests/bash/fixtures/check_31/present/plugins/mycelium/skills/goodskill/SKILL.md · 19 lines

What it actually says

Good Skill

This skill writes to .claude/canvas/purpose.yml (Update canvas/purpose.yml).

Preflight: Read target canvas file

Before any canvas write, this skill reads the target file first per the Read-before-Write hard rule (anti-pattern #7 instance #5 prevention).

Read .claude/canvas/purpose.yml (limit: 1 for Edit, full Read for Write)

Then proceeds with the write.

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. yesterday First seen · 19 lines · 23 tokens per session scan A 0d73eaf20d6f

Subscribe to this mod's changes

goodskill is a skill published in the GitHub repository haabe/mycelium (45 stars, last pushed today), licensed MIT. It adds 23 tokens to every session and 124 once invoked, about $0.0001 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 2026-09-03.

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