mcp-builder

mcp-builder is a cursor rule for Cursor from MN-Lizard-Team/aiyu-multi-agent. It costs 20 tokens per session (782 once invoked), scanned A, original, Apache-2.0.

A guide to building MCP servers. MCP, or Model Context Protocol, is a standard way for AI systems to connect to external tools and data.

In plain words
What is it for?
It is for planning MCP server structure, transport methods, tool schemas, resources, and prompt templates.
Why use it?
It helps developers design consistent tools, readable data resources, prompts, inputs, and outputs for AI integrations.

Cursor rule for Cursor

Written for Cursor: installed under .cursor/. Also seen: mentions Cursor.

Good fit It is for planning MCP server structure, transport methods, tool schemas, resources, and prompt templates.

Compare 6 cursor rules from other repositories ↓
Install with agentmods
npx agentmods add rules/mn-lizard-team/aiyu-multi-agent/mcp-builder
Install

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.

Clone the repo
git clone --depth 1 https://github.com/MN-Lizard-Team/aiyu-multi-agent

Made for: Cursor.

Wrote 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.

agentmods badge for mcp-builder

README.md
[![agentmods](https://agentmods.dev/badge/rules/mn-lizard-team/aiyu-multi-agent/mcp-builder.svg)](https://agentmods.dev/rules/mn-lizard-team/aiyu-multi-agent/mcp-builder)
Your own site
<a href="https://agentmods.dev/rules/mn-lizard-team/aiyu-multi-agent/mcp-builder"><img src="https://agentmods.dev/badge/rules/mn-lizard-team/aiyu-multi-agent/mcp-builder.svg" alt="Measured on agentmods" height="20"></a>
Per session 20 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 782 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00020 $0.00782
Opus 5 $0.00010 $0.00391
Sonnet 5 $0.00004 $0.00156
Haiku 4.5 $0.00002 $0.00078

Measured 4d ago against content hash e1c2921fee3d, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

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 4d 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.

.cursor/rules/skills/mcp-builder.mdc · 180 lines

How it starts

The opening of the file, as written. The whole thing — 180 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Skill: mcp-builder

Cursor Agent-Requested Rule — applied when AI determines relevance.


MCP Builder

Principles for building MCP servers.


1. MCP Overview

What is MCP?

Model Context Protocol - standard for connecting AI systems with external tools and data sources.

Core Concepts

Concept Purpose
Tools Functions AI can call
Resources Data AI can read
Prompts Pre-defined prompt templates

2. Server Architecture

Project Structure

my-mcp-server/
├── src/
│   └── index.ts      # Main entry
├── package.json
└── tsconfig.json

Transport Types

Type Use
Stdio Local, CLI-based
SSE Web-based, streaming
WebSocket Real-time, bidirectional

3. Tool Design Principles

Good Tool Design

Principle Description
Clear name Action-oriented (get_weather, create_user)
Single purpose One thing well
Validated input Schema with types and descriptions
Structured output Predictable response format

Input Schema Design

Field Required?
Type Yes - object
Properties Define each param
Required List mandatory params
Description Human-readable

4. Resource Patterns

Resource Types

Type Use
Static Fixed data (config, docs)
Dynamic Generated on request
Template URI with parameters

URI Patterns

Pattern Example
Fixed docs://readme
Parameterized users://{userId}
Collection files://project/*

5. Error Handling

Error Types

Situation Response
Invalid params Validation error message
Not found Clear "not found"
Server error Generic error, log details

Best Practices

  • Return structured errors
  • Don't expose internal details
  • Log for debugging
  • Provide actionable messages

Read the full file on GitHub · 180 lines

Changes

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.

  1. 4d ago First seen · 180 lines · 20 tokens per session scan A e1c2921fee3d

Subscribe to this mod's changes

mcp-builder is a cursor rule published in the GitHub repository MN-Lizard-Team/aiyu-multi-agent (7 stars, last pushed 3mo ago), licensed Apache-2.0. It adds 20 tokens to every session and 782 once invoked, about $0.0001 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 2026-09-03.