fastmcp

SKILL.md preview

---
name: fastmcp
description: Build, test, inspect, install, and deploy MCP servers with FastMCP in Python. Use when creating a new MCP server, wrapping an API or database as MCP tools, exposing resources or prompts, or preparing a FastMCP server for Claude Code, Cursor, or HTTP deployment.
version: 1.0.0
author: Hermes Agent
license: MIT
platforms: [linux, macos, windows]
metadata:
  hermes:
    tags: [MCP, FastMCP, Python, Tools, Resources, Prompts, Deployment]
    homepage: https://gofastmcp.com
    related_skills: [native-mcp, mcporter]
prerequisites:
  commands: [python3]
---

# FastMCP

Build MCP servers in Python with FastMCP, validate them locally, install them into MCP clients, and deploy them as HTTP endpoints.

## When to Use

Use this skill when the task is to:

- create a new MCP server in Python
- wrap an API, database, CLI, or file-processing workflow as MCP tools
- expose resources or prompts in addition to tools
- smoke-test a server with the FastMCP CLI before wiring it into Hermes or another client
- install a server into Claude Code, Claude Desktop, Cursor, or a similar MCP client
- prepare a FastMCP server repo for HTTP deployment

Use `native-mcp` when the server already exists and only needs to be connected to Hermes. Use `mcporter` when the goal is ad-hoc CLI access to an existing MCP server instead of building one.

## Prerequisites

Install FastMCP in the working environment first:

```bash
pip install fastmcp
fastmcp version
```

For the API template, install `httpx` if it is not already present:

```bash
pip install httpx
```

## Included Files

### Templates

- `templates/api_wrapper.py` - REST API wrapper with auth header support
- `templates/database_server.py` - read-only SQLite query server
- `templates/file_processor.py` - text-file inspection and search server

### Scripts

- `scripts/scaffold_fastmcp.py` - copy a starter template and replace the server name placeholder

### References

- `references/fastmcp-cli.md` - FastMCP CLI workflow, installation targets, and deployment checks

## Workflow

### 1. Pick the Smallest Viable Server Shape

Choose the narrowest useful surface area first:

- API wrapper: start with 1-3 high-value endpoints, not the whole API
- database server: expose read-only introspection and a constrained query path
- file processor: expose deterministic operations with explicit path arguments
- prompts/resources: add only when the client needs reusable prompt templates or discoverable documents

Prefer a thin server with good names, docstrings, and schemas over a large server with vague tools.

### 2. Scaffold from a Template

Copy a template directly or use the scaffold helper:

```bash
python ~/.hermes/skills/mcp/fastmcp/scripts/scaffold_fastmcp.py \
  --template api_wrapper \
  --name "Acme API" \
  --output ./acme_server.py
```

Available templates:

```bash
python ~/.hermes/skills/mcp/fastmcp/scripts/scaffold_fastmcp.py --list
```

If copying manually, replace `__SERVER_NAME__` with a real server name.

### 3. Implement Tools First

Start with `@mcp.tool` functions before adding resources or prompts.

Rules for tool design:

- Give every tool a concrete verb-based name
- Write docstrings as user-facing tool descriptions
- Keep parameters explicit and typed
- Return structured JSON-safe data where possible
- Validate unsafe inputs early
- Prefer read-only behavior by default for first versions

Good tool examples:

- `get_customer`
- `search_tickets`
- `describe_table`
- `summarize_text_file`

Weak tool examples:

- `run`
- `process`
- `do_thing`

### 4. Add Resources and Prompts Only When They Help

Add `@mcp.resource` when the client benefits from fetching stable read-only content such as schemas, policy docs, or generated reports.

Add `@mcp.prompt` when the server should provide a reusable prompt template for a known workflow.

Do not turn every document into a prompt. Prefer:

- tools for actions
- resources for data/document retrieval
- prompts for reusable LLM

…