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 hoblin/claude-ruby-marketplace --skill mcp-servergit clone --depth 1 https://github.com/hoblin/claude-ruby-marketplaceWrote 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/hoblin/claude-ruby-marketplace/mcp-server)<a href="https://agentmods.dev/skills/hoblin/claude-ruby-marketplace/mcp-server"><img src="https://agentmods.dev/badge/skills/hoblin/claude-ruby-marketplace/mcp-server.svg" alt="Measured on agentmods" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00098 | $0.01759 |
| Opus 5 | $0.00049 | $0.00879 |
| Sonnet 5 | $0.00020 | $0.00352 |
| Haiku 4.5 | $0.00010 | $0.00176 |
Grade A, and why
mcp-server 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 8d 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 — 185 lines — stays where its author put it; the contents beside it link to each section on GitHub.
MCP Ruby SDK - Server Development Guide
Build Model Context Protocol servers in Ruby using the official mcp gem (maintained by Anthropic and Shopify).
Design Philosophy
Information Provider, Not Analyzer
MCP servers provide structured data; LLMs do the reasoning. Return comprehensive frameworks and raw information—let the client perform analysis and context-dependent decisions.
"The MCP server's job is to be the world's best research assistant, not a competing analyst." — Matt Adams
Context Preservation
Agents have limited context windows. Every byte returned that wasn't requested is a byte that could have held useful context. Treat context preservation as a first-class design constraint.
Principles:
- Never return data that wasn't explicitly requested
- Mutations are quiet—return confirmations, not data dumps
- Explicit over implicit—associations only when asked
- Filter large datasets before returning (10,000 rows → 5 relevant rows)
Domain-Aligned Vocabulary
Tools should speak the language of your domain, not database/CRUD terminology. Agents are collaborators in your domain process, not database clients.
Example: A visual novel asset server uses create_image, make_sprite, place_character, explore_variations, compare_images—not generate, remove_background, composite, batch_generate, get_diff.
Tool Budget Management
Too many tools overwhelm agents and increase costs. Design toolsets around clear use cases, not API endpoint mirrors.
- Group related functionality intelligently
- Use lazy loading for large tool sets (150K tokens → 2K via on-demand discovery)
- Tool names ≤64 characters, descriptions narrow and unambiguous
Security: The Lethal Trifecta
Three capabilities that, when combined, create vulnerabilities (Simon Willison):
- Access to private data
- Exposure to untrusted content
- External communication capabilities
Required: Explicit user consent before tool invocation, clear UI showing exposed tools, alerts when tool descriptions change.
What ships with it
13 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.
- examples/dynamic_tools.rb 1012 B runs code
- examples/file_manager_tool.rb 2.3 KB runs code
- examples/http_client.rb 1.1 KB runs code
- examples/http_server.rb 2.3 KB runs code
- examples/rails_integration.rb 2.3 KB runs code
- examples/stdio_server.rb 2.6 KB runs code
- examples/streaming_client.rb 2.2 KB runs code
- references/gotchas.md 4.3 KB
- references/prompts.md 2.0 KB
- references/resources.md 1.2 KB
- references/server.md 3.8 KB
- references/tools.md 3.6 KB
- references/transport.md 2.8 KB
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.
- 8d ago First seen · 185 lines · 98 tokens per session scan A deef01101760
mcp-server is a skill published in the GitHub repository hoblin/claude-ruby-marketplace (37 stars, last pushed today), licensed MIT. It adds 98 tokens to every session and 1,759 once invoked, about $0.0005 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.
Other skills, from other repositories
ruzzy
Use when asked to set up and run coverage-guided fuzzing of Ruby code or C extensions with Ruzzy, producing crash reports or clean campaign summaries. Not for C/C++ fuzzing: use libfuzzer or libfuzzer.
rb:dry-rb-patterns
Applying dry-rb gems: dry-validation contracts, dry-types coercion, dry-monads Result/Maybe, dry-struct value objects, dry-transaction pipelines, dry-system DI.
rb:sequel-patterns
Applying Sequel ORM patterns: datasets, migrations, associations, plugins, transactions, Sequel-vs-AR boundary decisions.
rb:async-patterns
Implementing Ruby fiber concurrency: async gem, Falcon server, I/O-bound parallelism, fiber-safe locking.
rb:compound
Capturing a solved Ruby/Rails/Grape problem as reusable knowledge. YAML solution doc. Triggers: "compound this", "save this solution", "capture this fix".
ruby-idioms
Plain Ruby idioms: value objects, error handling, pattern matching, ractors, YJIT. Triggers: "frozen string literal", "plain Ruby code", "endless method", "value object". Do NOT use for: Rails patterns.