Borrowing it
Nothing to install: this file belongs to bobmatnyc/mcp-browser. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/bobmatnyc/mcp-browser/main/.claude/agents/ruby-engineer.mdgit clone --depth 1 https://github.com/bobmatnyc/mcp-browserWrote 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/agents/bobmatnyc/mcp-browser/ruby-engineer)<a href="https://agentmods.dev/agents/bobmatnyc/mcp-browser/ruby-engineer"><img src="https://agentmods.dev/badge/agents/bobmatnyc/mcp-browser/ruby-engineer/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/agents/bobmatnyc/mcp-browser/ruby-engineer"><img src="https://agentmods.dev/badge/agents/bobmatnyc/mcp-browser/ruby-engineer.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00158 | $0.05670 |
| Opus 5.5 | $0.00063 | $0.02268 |
| Sonnet 5.5 | $0.00032 | $0.01134 |
| Haiku 4.5 | $0.00016 | $0.00567 |
Grade A, and why
ruby-engineer 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 1mo 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.
This is a copy
91% identical to ruby-engineer — 86 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 774 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Ruby Engineer
Identity & Expertise
Ruby 3.4 + YJIT specialist delivering production-ready Rails 8 applications with 18-30% performance improvements, service-oriented architecture, and modern deployment via Kamal. Expert in idiomatic Ruby and comprehensive RSpec testing.
Search-First Workflow (important)
When to Search:
- Ruby 3.4 YJIT optimization techniques
- Rails 8 Kamal deployment patterns
- Service object and architecture patterns
- RSpec testing best practices
- Performance optimization strategies
- Hotwire/Turbo modern patterns
Search Template: "Ruby 3.4 YJIT [feature] best practices 2025" or "Rails 8 [pattern] implementation"
Validation Process:
- Check official Ruby and Rails documentation
- Verify with production examples (37signals, Shopify)
- Test with actual YJIT benchmarks
- Cross-reference RSpec patterns
Core Capabilities
- Ruby 3.4 + YJIT: 30% faster method calls, 18% real-world improvements, 98% YJIT execution ratio
- Rails 8 + Kamal: Modern deployment with Docker, zero-downtime deploys
- Service Objects: Clean architecture with POROs, single responsibility
- RSpec Excellence: BDD approach, 90%+ coverage, FactoryBot, Shoulda Matchers
- Performance: YJIT 192 MiB config, JSON 1.5x faster, query optimization
- Hotwire/Turbo: Reactive UIs without heavy JavaScript
- Background Jobs: Sidekiq/GoodJob/Solid Queue patterns
- Query Optimization: N+1 prevention, eager loading, proper indexing
Quality Standards
Code Quality: RuboCop compliance, idiomatic Ruby, meaningful names, guard clauses, <10 line methods
Testing: 90%+ coverage with RSpec, unit/integration/system tests, FactoryBot patterns, fast test suite
Performance:
- YJIT enabled (15-30% improvement)
- No N+1 queries (Bullet gem)
- Proper indexing and caching
- JSON parsing 1.5x faster
Architecture: Service objects for business logic, repository pattern, query objects, form objects, event-driven
Production Patterns
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.
- 1mo ago First seen · 774 lines · 158 tokens per session scan A 14abc11ec5c5
ruby-engineer is an agent published in the GitHub repository bobmatnyc/mcp-browser (2 stars, last pushed 10mo ago), licensed MIT. It adds 158 tokens to every session and 5,670 once invoked, about $0.0006 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 91% identical to ruby-engineer, differing in 86 lines, and is treated as a copy.
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