Expense Tracker MCP Server
Expense Tracker MCP Server
FastMCP (v3.x) と Python で構築された Model Context Protocol (MCP) サーバーで、Claude Desktop や MCP Inspector などの MCP 準拠クライアントに、経費記録用のツールとリソースを提供するように設計されています。
前提条件
Python: 3.10+ (Python 3.14 でテスト済み)
uv: 高速な Python パッケージインストーラー兼リゾルバー (astral.sh/uv)
Node.js:
v22.xまたはv24.x(LTS) — MCP Inspector UI に必要Claude Desktop (任意): Claude 内でツールを直接テストするため
Related MCP server: Demo MCP Server
セットアップとインストール
1. プロジェクトと環境を初期化する
# Initialize uv project (if starting fresh)
uv init .
# Install FastMCP
uv add fastmcp2. MCP Inspector UI 用の Node.js を準備する
MCP Inspector (@modelcontextprotocol/inspector) には Node.js v22.19.0+ または v24+ が必要です。nvm-windows を使用している場合:
nvm install lts
nvm use 24インスペクターをグローバルにインストールするか、npx にフェッチさせます:
npm install -g @modelcontextprotocol/inspector🛠 実行と開発
オプション A: インタラクティブな Web UI (MCP Inspector)
ホットリロード 付きで MCP Inspector の Web UI を起動するには:
uv run fastmcp dev inspector main.pyこのターミナルウィンドウは開いたままにしてください。
コンソールに、認証トークン付きのローカル URL が表示されます:
MCP Inspector Web is up and running at: http://127.0.0.1:6274?MCP_INSPECTOR_API_TOKEN=<token>ブラウザでそのリンクを開くと、ツールのテスト、スキーマの確認、リクエスト/レスポンスログのリアルタイム表示ができます。
オプション B: サーバーを直接実行する (STDIO)
標準 I/O モードで MCP サーバーを実行するには:
uv run fastmcp run main.py(または uv run python main.py)
🤖 Claude Desktop への接続
1. 設定ファイルの場所
Windows では、Claude Desktop の設定は次の場所に保存されています:
%APPDATA%\Claude\claude_desktop_config.json(完全なパス: C:\Users\<YourUsername>\AppData\Roaming\Claude\claude_desktop_config.json)
2. 設定内容
mcpServers の下に expense-server の定義を追加します。
注: Windows では、Claude Desktop のような GUI アプリケーションは、シェルの
PATHを引き継がないことが多いため、常にuv.exeの絶対パスを指定してください。
{
"mcpServers": {
"expense-server": {
"command": "C:\\Users\\hp\\AppData\\Local\\Python\\pythoncore-3.14-64\\Scripts\\uv.exe",
"args": [
"run",
"--directory",
"g:\\Projects\\expense-tracker-mcp-server",
"fastmcp",
"run",
"main.py"
]
}
}
}3. Claude Desktop を再起動する
Claude Desktop を完全終了します (時計の近くの Windows システムトレイから終了されることを確認してください)。
Claude Desktop を開き直します。
Settings > Developer で、
expense-serverが接続されていることを確認します。
🧰 利用可能なツール (現在の main.py)
ツール | パラメータ | 説明 |
|
|
|
|
| 2 つの数値を加算し、その合計を返します。 |
トラブルシューティング
1. Unknown command "main.py". Available commands: inspector, apps.
FastMCP 3.x では、fastmcp dev はコマンドグループです。fastmcp dev main.py の代わりに fastmcp dev inspector main.py を使用してください。
2. node:util does not provide an export named 'styleText'
Node.js が v20.12 より古いです。nvm install lts && nvm use 24 で Node v22+ または v24+ に更新してください。
3. Cannot find native binding (npm optional dependencies bug)
Node のバージョン切り替えによる npx キャッシュの破損です。次を実行してください:
npm cache clean --force
Remove-Item -Recurse -Force "$env:LOCALAPPDATA\npm-cache\_npx" -ErrorAction SilentlyContinue
npm install -g @modelcontextprotocol/inspectorAvailable Tools
2 toolsadd_numbersA
Add two numbers together.
| Name | Required | Description | Default |
|---|---|---|---|
| a | Yes | ||
| b | Yes |
Output Schema
| Name | Required | Description |
|---|---|---|
| result | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It states the operation but does not explicitly mention that it is pure, has no side effects, or what the return value is. While obvious for addition, it falls short of full transparency.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, direct sentence with zero filler. It is front-loaded and every word earns its place, exemplifying appropriate conciseness.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a trivial addition tool with a clear input schema and an output schema (as indicated by the signal), the description is largely sufficient. It lacks explicit mention of edge cases or preconditions, but none are expected for this operation, making it nearly complete.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0%—the description does not mention parameters by name or add any nuance. The schema already declares a and b as required numbers, but the description adds no value beyond that, failing to compensate for the low coverage.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description 'Add two numbers together' uses a specific verb and resource, clearly stating exactly what the tool does. It is distinct from siblings like roll_dice and add_expense, so agents can easily differentiate.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description gives no guidance on when to use this tool versus alternatives, nor any exclusions. There is no context about when addition is appropriate or not, leaving the agent to infer usage from the name and schema alone.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
roll_diceA
Roll n_dice 6-sided dice and return the results.
| Name | Required | Description | Default |
|---|---|---|---|
| n_dice | No |
Output Schema
| Name | Required | Description |
|---|---|---|
| result | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden of behavioral disclosure. It correctly implies a random stochastic process and states the output ('return the results'), but does not explicitly mention randomness, the range of outcomes (1–6 per die), or that subsequent calls produce independent results. This is adequate for a simple tool but lacks any deeper context.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single sentence, front-loaded with the core action, and contains no filler words. Every term contributes to understanding the tool's behavior.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the low complexity (one parameter, simple output) and the presence of an output schema, the description is complete enough. It explains the parameter's role and the action's purpose. It could mention the non-deterministic nature more explicitly, but that is implicit for a dice-rolling tool, and the output schema likely covers return formatting.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The input schema has zero description coverage for the parameter n_dice, so the description must compensate. It does so by framing n_dice as the number of dice to roll, adding semantic meaning to an otherwise bare integer field. However, it does not specify constraints like minimum value or positivity, which would have improved clarity further.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description states a clear, specific action: 'Roll n_dice 6-sided dice and return the results.' The verb 'Roll' and resource 'dice' are unambiguous, and the tool is easily distinguished from siblings like add_numbers or list_expenses, which handle arithmetic or expense management.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
There is no guidance about when to use this tool versus alternatives, nor any exclusions or prerequisites. Sibling tools are unrelated, but the description provides no context for selection, leaving the agent to infer its suitability from the name alone.
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.
2 tool updates
v0.1.0- First observed
add_numbers - First observed
roll_dice
TDQS
Scored across 2 tools
The two tools have completely disjoint purposes—one rolls dice and the other adds numbers. There is no ambiguity between them and no chance of an agent misselecting one for the other.
Both tool names follow the same verb_noun snake_case pattern: roll_dice and add_numbers. The naming is predictable and straightforward.
A server named 'Expense Tracker' offers only two tools that perform unrelated operations (dice rolling and arithmetic). This is a severe mismatch between scope and purpose, making the count completely inappropriate.
The tools do not cover any expense tracking functionality whatsoever—no add expense, list expenses, delete expense, or summaries. The surface is entirely incomplete for the stated domain.
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