A set of guidance for designing and building MCP servers with FastMCP, a Python framework for MCP tools.

Planning MCP architecture, designing agent tools, using middleware, managing context, composing FastMCP servers, and adding Logfire observability.

It helps address decisions about tool design, server structure, context usage, and monitoring.

How dsfaccini/siigo-mcp configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to dsfaccini/siigo-mcp. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/dsfaccini/siigo-mcp/main/.claude/skills/technical/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/dsfaccini/siigo-mcp

Made for: Claude Code.

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/dsfaccini/siigo-mcp/technical/github.svg)](https://agentmods.dev/skills/dsfaccini/siigo-mcp/technical)

Your own site

<a href="https://agentmods.dev/skills/dsfaccini/siigo-mcp/technical"><img src="https://agentmods.dev/badge/skills/dsfaccini/siigo-mcp/technical/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/dsfaccini/siigo-mcp/technical"><img src="https://agentmods.dev/badge/skills/dsfaccini/siigo-mcp/technical.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 35 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 587 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.

Model	Per session	Once invoked
Fable 5.1	$0.00035	$0.00587
Opus 5.5	$0.00014	$0.00235
Sonnet 5.5	$0.00007	$0.00117
Haiku 4.5	$0.00003	$0.00059

Measured 2mo ago against content hash 19a1bcc6c29c, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

technical 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 2mo 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.

.claude/skills/technical/SKILL.md · 87 lines

How it starts

The opening of the file, as written. The whole thing — 87 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Technical MCP Expert

Research-First Implementation skill for MCP/FastMCP best practices.

When to Use

Invoke this skill when working on:

MCP server architecture decisions
Tool design and progressive disclosure
Context management optimization
FastMCP middleware and composition
Logfire observability patterns

Key Resources

FastMCP

FastMCP Docs - Official documentation
FastMCP GitHub - Source and examples
Tool Transformation - Making tools LLM-friendly
Middleware - Cross-cutting concerns

MCP Protocol

MCP Best Practices - Architectural guidelines
MCP Spec - Latest protocol specification

Progressive Disclosure

Lazy MCP Proxy - 85-93% context reduction
Pattern: Discover → Load → Execute (don't expose all tools upfront)
Use gateway pattern for 5+ related capabilities

FastMCP Patterns

Server Composition

# Dynamic composition (live links)
mcp.mount("customers", customer_server)

# Static composition (snapshot)
mcp.import_server(shared_utils)

Dependency Injection

@asynccontextmanager
async def get_client() -> AsyncIterator[Client]:
    client = Client()
    try:
        yield client
    finally:
        await client.close()

@mcp.tool
async def my_tool(client: Client = Depends(get_client)) -> str:
    return await client.fetch()

Context Usage

@mcp.tool
async def long_task(query: str, ctx: Context) -> str:
    ctx.log.info(f"Processing: {query}")
    ctx.report_progress(0.5)
    return "result"

Logfire Integration

import logfire
logfire.configure()

# Automatic instrumentation for:
# - HTTP requests (httpx)
# - Async operations
# - Custom spans with @logfire.instrument

Read the full file on GitHub · 87 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.

2mo ago First seen · 87 lines · 35 tokens per session scan A 19a1bcc6c29c

Subscribe to this mod's changes

technical is a skill published in the GitHub repository dsfaccini/siigo-mcp (1 stars, last pushed 10mo ago), licensed MIT. It adds 35 tokens to every session and 587 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-08-31.

Building agents

technical next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
technicaldsfaccini/siigo-mcp	Skill	1	10mo ago	MIT	A	35	Claude Code
imagegenopenai/codex	Skill	133k	yesterday	Apache-2.0	A	113	Codex
playwright-climicrosoft/playwright	Skill	99k	yesterday	Apache-2.0	A	19	Claude Code
local-ai-agentsmicrosoft/ai-agents-for-beginners	Skill	79k	4d ago	MIT	A	200	Claude Code, Codex
systematic-debuggingobra/superpowers	Skill	313k	3d ago	MIT	A	21	Claude Code
next-cache-components-adoptionvercel/next.js	Skill	143k	yesterday	MIT	A	95	Claude Code
next-partial-prefetching-adoptionvercel/next.js	Skill	143k	yesterday	MIT	A	103	Claude Code

siigo-mcp: Skill for Claude Code