Expense Tracker MCP Server
Expense Tracker MCP Server
Un servidor del Model Context Protocol (MCP) construido con FastMCP (v3.x) y Python, diseñado para proporcionar herramientas y recursos para el seguimiento de gastos a clientes compatibles con MCP, como Claude Desktop y MCP Inspector.
📋 Requisitos previos
Python: 3.10+ (probado con Python 3.14)
uv: instalador y resolvedor rápido de paquetes Python (astral.sh/uv)
Node.js:
v22.xov24.x(LTS) — Requerido para el UI del MCP InspectorClaude Desktop (opcional): para probar las herramientas directamente en Claude
Related MCP server: Demo MCP Server
🚀 Configuración e instalación
1. Inicializar el proyecto y el entorno
# Initialize uv project (if starting fresh)
uv init .
# Install FastMCP
uv add fastmcp2. Preparar Node.js para el UI del MCP Inspector
El MCP Inspector (@modelcontextprotocol/inspector) requiere Node.js v22.19.0+ o v24+. Si se usa nvm-windows:
nvm install lts
nvm use 24Instala el inspector globalmente o permite que npx lo obtenga:
npm install -g @modelcontextprotocol/inspector🛠️ Ejecución y desarrollo
Opción A: UI web interactiva (MCP Inspector)
Para ejecutar la UI web del MCP Inspector con recarga en caliente:
uv run fastmcp dev inspector main.pyMantén esta ventana de terminal abierta.
La consola mostrará una URL local con un token de autenticación:
MCP Inspector Web is up and running at: http://127.0.0.1:6274?MCP_INSPECTOR_API_TOKEN=<token>Abre ese enlace en tu navegador para probar herramientas, inspeccionar esquemas y ver registros de solicitudes/respuestas en tiempo real.
Opción B: Ejecutar el servidor directamente (STDIO)
Para ejecutar el servidor MCP en modo de entrada/salida estándar:
uv run fastmcp run main.py(o uv run python main.py)
🤖 Conexión con Claude Desktop
1. Ubicación del archivo de configuración
En Windows, la configuración de Claude Desktop se almacena en:
%APPDATA%\Claude\claude_desktop_config.json(Ruta completa: C:\Users\<YourUsername>\AppData\Roaming\Claude\claude_desktop_config.json)
2. Configuración
Agrega la definición de expense-server bajo mcpServers.
Nota: En Windows, las aplicaciones GUI como Claude Desktop suelen no heredar el
PATHde la consola. Especifica siempre la ruta absoluta auv.exe.
{
"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. Reinicia Claude Desktop
Cierra completamente Claude Desktop (asegúrate de salir desde la bandeja del sistema de Windows, junto al reloj).
Vuelve a abrir Claude Desktop.
Revisa Configuración > Desarrollador para verificar que
expense-serveresté conectado.
🧰 Herramientas disponibles (main.py actual)
Herramienta | Parámetros | Descripción |
|
| Lanza |
|
| Suma dos números y devuelve la suma. |
🔧 Solución de problemas
1. Unknown command "main.py". Available commands: inspector, apps.
En FastMCP 3.x, fastmcp dev es un grupo de comandos. Usa fastmcp dev inspector main.py en lugar de fastmcp dev main.py.
2. node:util does not provide an export named 'styleText'
La versión de Node.js es anterior a v20.12. Actualiza a Node v22+ o v24+ mediante nvm install lts && nvm use 24.
3. Cannot find native binding (npm optional dependencies bug)
Caché de npm dañada al cambiar de versiones de Node. Ejecuta:
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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