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 ombulabs/claude-code_dual-boot-skill --skill dual-bootgit clone --depth 1 https://github.com/ombulabs/claude-code_dual-boot-skillWrote 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/ombulabs/claude-code_dual-boot-skill/dual-boot)<a href="https://agentmods.dev/skills/ombulabs/claude-code_dual-boot-skill/dual-boot"><img src="https://agentmods.dev/badge/skills/ombulabs/claude-code_dual-boot-skill/dual-boot.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00084 | $0.02541 |
| Opus 5 | $0.00042 | $0.01270 |
| Sonnet 5 | $0.00017 | $0.00508 |
| Haiku 4.5 | $0.00008 | $0.00254 |
Grade A, and why
dual-boot 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 7d 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 — 202 lines — stays where its author put it; the contents beside it link to each section on GitHub.
When invoked via /dual-boot, follow the setup workflow in workflows/setup-workflow.md to set up dual-boot for this project. If the user provides version arguments (e.g. /dual-boot 7.0 7.1), use them as the current and target versions. If no arguments are provided, detect the current version from the Gemfile and ask the user for the target version.
Dual-Boot Skill
- Purpose: Set up and manage dual-boot environments for Rails, Ruby, or core Gemfile dependencies using the
next_railsgem - Key Gem: next_rails
- Methodology: Based on FastRuby.io upgrade best practices and "The Complete Guide to Upgrade Rails" ebook
- Attribution: Content based on "The Complete Guide to Upgrade Rails" by FastRuby.io (OmbuLabs)
Overview
Dual-booting allows a Ruby application to maintain two sets of dependencies simultaneously. While most commonly used for Rails version upgrades, the same approach works for upgrading Ruby versions or any core dependency in your Gemfile (e.g., sidekiq, devise, pg).
This skill helps you:
- Set up dual-boot with the
next_railsgem - Configure the Gemfile to support two versions of Rails, Ruby, or other key dependencies
- Branch application code using
NextRails.next? - Configure CI to test against both dependency sets
- Clean up dual-boot code after the upgrade is complete
CRITICAL: Always Use NextRails.next? — Never Use Feature Detection
When code would break on one version and needs a different implementation on the other, always use NextRails.next? from the next_rails gem to branch — never feature detection. Do not use respond_to?, defined?, const_defined?, or any other feature-detection pattern for version branching.
Why feature detection is problematic:
- Hard to understand: readers must know which version introduced a method or constant to grasp the intent
- Hard to maintain:
respond_to?/defined?checks pile up and become impossible to clean up because their purpose is lost - Fragile: may give wrong results if gems monkey-patch methods or constants in or out
- Obscures intent: the code says "does this exist?" when it means "are we on the next Rails version?"
What ships with it
8 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.
- 7d ago First seen · 202 lines · 84 tokens per session scan A cd24e4b8f834
dual-boot is a skill published in the GitHub repository ombulabs/claude-code_dual-boot-skill (13 stars, last pushed 2mo ago), licensed MIT. It adds 84 tokens to every session and 2,541 once invoked, about $0.0004 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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