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 vibeinging/YiYi --skill mcp_buildergit clone --depth 1 https://github.com/vibeinging/YiYiWrote 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/vibeinging/yiyi/mcp_builder)<a href="https://agentmods.dev/skills/vibeinging/yiyi/mcp_builder"><img src="https://agentmods.dev/badge/skills/vibeinging/yiyi/mcp_builder.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 | $0.00037 | $0.00345 |
| Opus 5 | $0.00018 | $0.00172 |
| Sonnet 5 | $0.00007 | $0.00069 |
| Haiku 4.5 | $0.00004 | $0.00034 |
Grade A, and why
mcp_builder 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.
What it actually says
MCP Server Development Guide
Overview
Create MCP (Model Context Protocol) servers that enable LLMs to interact with external services through well-designed tools.
High-Level Workflow
Phase 1: Deep Research and Planning
- Study MCP Protocol Documentation:
https://modelcontextprotocol.io/sitemap.xml - Recommended stack: TypeScript with Streamable HTTP for remote, stdio for local
- Load framework docs from
reference/directory
Phase 2: Implementation
- Set up project structure (see language-specific guides in
reference/) - Implement core infrastructure: API client, error handling, response formatting, pagination
- Implement tools with proper input/output schemas and annotations
Phase 3: Review and Test
- Code quality review (DRY, error handling, type coverage)
- Build and test with MCP Inspector:
npx @modelcontextprotocol/inspector
Phase 4: Create Evaluations
- Create 10 complex, realistic evaluation questions
- Output as XML evaluation file
Reference Files in reference/ directory:
mcp_best_practices.md- Core guidelinesnode_mcp_server.md- TypeScript patterns and examplespython_mcp_server.md- Python patterns and examplesevaluation.md- Evaluation creation guide
What ships with it
7 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.
- 8d ago First seen · 45 lines · 37 tokens per session scan A d99179e0238b
mcp_builder is a skill published in the GitHub repository vibeinging/YiYi (51 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 37 tokens to every session and 345 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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