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toy-mcp-server

toy-mcp-server

by kritikatripathi03
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

toy-mcp-server

一个从零构建的最小化 Model Context Protocol (MCP) 服务器，用来理解 MCP 实际的工作方式——不用脚手架生成器、不用模板，只需用到 SDK。

这是我的第一个动手实践 MCP 项目：包含两个工具和一个资源，通过 stdio 接入 Claude Desktop。

它能做什么

MCP 让 LLM 客户端（比如 Claude Desktop）调用在你本机上运行的函数，而不只是从训练数据中生成文本。本服务器提供：

工具（Claude 可以调用的函数）：

  • roll_dice — 掷 N 个骰子，骰子面数可配置

  • flip_coin — 掷 N 次硬币

资源（Claude 可以获取的只读数据）：

  • server-info — 服务器的基础元数据（名称、用途、启动时间）

Related MCP server: Random-Generator

为什么存在

LLM 无法访问训练数据之外的任何内容，并且默认情况下无法 执行 任何操作——它们只会生成文本。MCP 是一种以标准方式为模型提供以下能力的途径：

  • 能力 — 模型自身不具备的能力（例如真正的随机性——众所周知，LLM 在随机选数字方面表现非常糟糕）

  • 访问权限 — 访问模型无法知道的实时或私有数据

在把 MCP 服务器指向真实目标（数据库、带认证的 API 等）之前，这个项目是验证这一想法的一个安全小型沙箱。

技术栈

  • TypeScript

  • @modelcontextprotocol/sdk — 官方 MCP SDK

  • zod — 工具参数的运行时 schema 校验

  • stdio 传输（与 Claude Desktop 的本地子进程通信）

项目结构

toy-mcp-server/
├── src/
│   └── index.ts       # server setup, tools, and resource
├── build/              # compiled output (git-ignored)
├── package.json
├── tsconfig.json
└── README.md

设置

1. 安装依赖

npm install

2. 构建

npm run build

3. 连接到 Claude Desktop

找到你的 Claude Desktop 配置文件：

  • macOS：~/Library/Application Support/Claude/claude_desktop_config.json

  • Windows：通常位于 %LOCALAPPDATA%\Packages\<Claude package folder>\LocalCache\Roaming\Claude\claude_desktop_config.json —— 具体路径可能因安装方式不同（Microsoft Store 与直接安装）而异。可靠的查找方式是：打开 Claude Desktop → Settings → Developer → Local MCP servers → Edit Config，这会打开应用实际读取的确切文件。

在 mcpServers 下合并这个服务器（合并到已有文件中，而非覆盖整个文件）：

{
  "mcpServers": {
    "toy-mcp-server": {
      "command": "node",
      "args": ["/absolute/path/to/toy-mcp-server/build/index.js"]
    }
  }
}

请把路径替换为你机器上 build/index.js 的实际绝对路径。在 Windows 上，需要在 JSON 字符串中对反斜杠进行转义（\\）。

4. 重启 Claude Desktop

完全退出（不是只关闭窗口）后重新打开。检查 Settings → Developer → Local MCP servers，确认 toy-mcp-server 显示为已连接。

5. 试一试

在聊天中试着输入：

  • “把 3 个六面骰子掷一下”

  • “把一枚硬币抛 10 次”

你应该会在回复上方看到一个小的工具调用指示器（例如 Roll Dice），从而确认 Claude 确实调用了工具，而不是猜测一个答案。

简单工作原理

  • McpServer — 向任何连接过来的客户端声明服务器能力的对象

  • registerTool(name, config, handler) — 注册一个可调用函数。config.inputSchema 在 handler 执行前使用 Zod 校验模型发送的任何参数

  • registerResource(name, uri, config, handler) — 注册通过 URI 寻址的只读数据，无需参数即可获取

  • StdioServerTransport — 即通信格式：Claude Desktop 将该文件作为子进程启动，并通过 stdin/stdout 使用 JSON-RPC 通信。由于 stdout 是实际的协议通道，console.log 在这里绝对不能用于日志输出——改用 console.error（stderr）

下一步

  • 将 toy 工具替换为真正连接数据库的工具（通过 Prisma 连接 Postgres）

  • 添加一个基于 GitHub 的工具（如 list_open_prs），练习基于 token 的认证

  • 探索 Streamable HTTP 传输，将服务部署到远端而非本地运行

许可证

MIT

Available Tools

2 tools
flip_coinFlip CoinB

Flip a coin one or more times

NameRequiredDescriptionDefault
timesNoNumber of flips

TDQS

B3.2/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full burden of disclosing behavior. It merely says 'Flip a coin one or more times' without mentioning that the outcome is random, what the return format is (e.g., 'heads'/'tails'), or any side effects. The agent is left to guess the result structure.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, efficient sentence that states the action and the parameter scope. There is zero wasted text, and the core information is front-loaded. It is appropriately concise for a trivial tool.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given there is no output schema, the description should explain what the tool returns (e.g., results of each flip). It omits any mention of return values or randomness, leaving the agent with incomplete information to use the tool correctly. For a tool this simple, more context is still needed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The single parameter 'times' is fully described in the schema ('Number of flips'), covering 100% of parameters. The tool description repeats the concept ('one or more times') but adds no extra meaning beyond what the schema already provides, so the baseline score of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource ('Flip a coin') and adds the scope 'one or more times', which distinguishes it from the sibling roll_dice by naming the object of the action. An agent can clearly identify what this tool does.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance is given about when to use this tool versus roll_dice. The description only states the action, leaving the agent to infer from the name that this is for coins rather than dice. No exclusions, prerequisites, or alternative-routing hints are provided.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

roll_diceRoll DiceB

Roll one or more dice with a given number of sides

NameRequiredDescriptionDefault
countNoNumber of dice to roll
sidesNoNumber of sides per die

TDQS

B3.2/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries full responsibility for behavioral disclosure. It does not mention that the result is random, that it is a safe non-mutating operation, or any other behavioral trait beyond the literal act of rolling. This is a significant gap for a tool whose entire purpose is random generation.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single concise sentence with no waste. The core action is front-loaded. It is appropriately sized for a tool with only two parameters, though it could have been slightly more informative without losing conciseness.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple tool with two parameters fully documented in the schema, the description is reasonably complete. However, the lack of any mention of randomness or return behavior (even though no output schema is provided) leaves a small but notable gap. An agent might not know the outcome is random without prior knowledge.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents both parameters (count and sides) with defaults, minimums, and maximums. The description adds no semantic meaning beyond what the schema provides, which meets the baseline of 3.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states exactly what the tool does: 'Roll one or more dice with a given number of sides'. It uses a specific verb (roll) and resource (dice), and clearly distinguishes from the sibling flip_coin, since dice and coins are different objects.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance on when to use this tool versus the sibling flip_coin. The context implies dice vs coin, but the description does not explicitly state that this is for dice and flip_coin is for coins, nor does it mention any exclusions or alternative conditions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections.

  1. 2 tool updatesv1.0.0
    • First observedflip_coin
    • First observedroll_dice
Deploy Server
One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

TDQS

A3.6/5.0

Scored across 2 tools

Disambiguation5/5

The two tools, roll_dice and flip_coin, are completely distinct in their purpose and behavior. There is no overlap or ambiguity, making it trivial for an agent to select the correct tool.

Naming Consistency5/5

Both tool names follow the same verb_noun pattern (roll_dice, flip_coin), using snake_case and clear action-object structure. This is perfectly consistent and predictable.

Tool Count4/5

With only 2 tools, the server is minimal, but given its explicit 'toy' purpose and narrow domain (random chance events), this count is appropriate and focused. It is slightly thin by general standards but well-scoped for a toy.

Completeness4/5

The tool surface covers the two most common random generators (dice and coin flips). While a generic random number generator or card draw might be expected in a broader utilities server, for a toy server focused on simple chance, these tools are sufficient and leave no obvious dead ends.

Maintenance

ActivityStale
ResponsivenessNo recent community issues

Resources

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