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 agentmods add skills/st0012/ruby-skills/ruby-version-managernpx skills add st0012/ruby-skills --skill ruby-version-managergit clone --depth 1 https://github.com/st0012/ruby-skillsWhat 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 | $0.00049 | $0.01394 |
| Opus 5 | $0.00024 | $0.00697 |
| Sonnet 5 | $0.00010 | $0.00279 |
| Haiku 4.5 | $0.00005 | $0.00139 |
Grade A, and why
ruby-version-manager scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 144 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Ruby Version Manager Skill
Detects and configures Ruby version managers for proper environment setup.
When to Use
Run detect.sh IMMEDIATELY when:
- Starting work in a directory with
Gemfile,.ruby-version, or.tool-versions - Before your first Ruby command (
ruby,bundle,gem,rake,rails,rspec, etc.) - When switching between Ruby projects
Do NOT wait for commands to fail or user requests. Proactive detection prevents version mismatch errors.
Always chain activation with commands: ACTIVATION_COMMAND && ruby_command
Usage
Step 1: Run detect.sh
Run detect.sh from this skill's directory (path provided by session-start hook).
Step 2: Parse Output
The script outputs key=value pairs:
VERSION_MANAGER=rbenv
PROJECT_RUBY_VERSION=3.2.0
VERSION_AVAILABLE=true
ACTIVATION_COMMAND=eval "$(rbenv init -)"
Step 3: Execute Ruby Commands
Chain ACTIVATION_COMMAND with your Ruby command:
eval "$(rbenv init -)" && bundle install
eval "$(rbenv init -)" && bundle exec rspec
Run detect.sh once per project session; reuse ACTIVATION_COMMAND for subsequent commands.
Output Variables
| Variable | Description |
|---|---|
VERSION_MANAGER |
Detected: shadowenv, chruby, rbenv, rvm, asdf, rv, mise, or none |
VERSION_MANAGER_PATH |
Installation path |
PROJECT_RUBY_VERSION |
Version required by project |
PROJECT_VERSION_SOURCE |
Source file (.ruby-version, .tool-versions, .mise.toml, Gemfile) |
RUBY_ENGINE |
Implementation (ruby, truffleruby, jruby) |
INSTALLED_RUBIES |
Comma-separated available versions |
VERSION_AVAILABLE |
true/false - whether requested version is installed |
ACTIVATION_COMMAND |
Shell command to activate the manager |
SYSTEM_RUBY_VERSION |
System Ruby (when VERSION_MANAGER=none) |
WARNING |
Environment warnings |
NEEDS_USER_CHOICE |
true when multiple managers detected without preference |
AVAILABLE_MANAGERS |
List of detected managers (when NEEDS_USER_CHOICE=true) |
NEEDS_VERSION_CONFIRM |
true when no version specifier found |
SUGGESTED_VERSION |
Latest installed Ruby (when NEEDS_VERSION_CONFIRM=true) |
What ships with it
4 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.
- 2d ago First seen · 144 lines · 49 tokens per session scan A a8488b1c1d6a
ruby-version-manager is a skill published in the GitHub repository st0012/ruby-skills (125 stars, last pushed 2mo ago), licensed MIT. It adds 49 tokens to every session and 1,394 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.
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