FastMCP is a Python framework for building Model Context Protocol applications, which connect language models with tools and data through servers and clients. Developers use it to expose Python functions as tools, connect to local or remote MCP servers, and build interactive tool interfaces. The catalogue includes eight skills, three instructions, two rules, one setting, and one hook for FastMCP.
Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add PrefectHQ/fastmcp --skill fastmcp-servergit clone --depth 1 https://github.com/PrefectHQ/fastmcpWrote 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.
[](https://agentmods.dev/skills/prefecthq/fastmcp/fastmcp-server)<a href="https://agentmods.dev/skills/prefecthq/fastmcp/fastmcp-server"><img src="https://agentmods.dev/badge/skills/prefecthq/fastmcp/fastmcp-server/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.
<a href="https://agentmods.dev/skills/prefecthq/fastmcp/fastmcp-server"><img src="https://agentmods.dev/badge/skills/prefecthq/fastmcp/fastmcp-server.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00027 | $0.01099 |
| Opus 5.5 | $0.00011 | $0.00440 |
| Sonnet 5.5 | $0.00005 | $0.00220 |
| Haiku 4.5 | $0.00003 | $0.00110 |
Grade A, and why
fastmcp-server 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 2d 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.
How it starts
The opening of the file, as written. The whole thing — 97 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Authoring MCP servers with FastMCP
Find the current API
Check the project's installed FastMCP version and dependency constraints.
Fetch the documentation index and read the
relevant pages for that version. The index includes versioned documentation;
select /v3/ pages for FastMCP 3 and unversioned pages for FastMCP 4. Read
individual pages through their .md URLs instead of loading llms-full.txt.
For APIs newer than the installed release, check that release's source or
signatures. Preserve the project's dependency constraints unless an upgrade is
part of the request. For a new project, check the current stable release before
choosing a dependency.
Use the standalone fastmcp package. Its API differs from
mcp.server.fastmcp in the Python MCP SDK.
Author the server
Choose the MCP interface to suit what the server exposes: tools for callable
operations, resources for addressable content, and prompts for reusable message
templates. FastMCP derives tool schemas from Python annotations and descriptions;
use Literal or enums for finite choices and Field descriptions for parameter
semantics. SDK wrappers need to preserve signatures and docstrings, for example
with functools.wraps, or discovery loses that information. Inspect the schema
the client receives, especially after transforms or custom discovery rendering:
requiredness, enum values, and nested fields can disappear from a summary.
Let the intended client tasks guide tool boundaries, descriptions, and result shape. Give clients enough context to use results and recover from errors. The right granularity depends on the service; generated API tools, custom tools, and compositions can all be appropriate.
For paginated or bounded results, expose whether the answer is complete and how
to continue. An upstream failure is not an empty result. Return useful recovery
information through tool errors rather than a successful-looking payload. Use
ToolError, ResourceError, or PromptError from fastmcp.exceptions for
intentional client-facing messages. With mask_error_details=True, ordinary
exceptions such as ValueError lose their messages; do not put sensitive backend
details in the explicit error types, whose messages remain visible.
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.
- 2d ago First seen · 97 lines · 27 tokens per session scan A 00d619fded80
fastmcp-server is a skill published in the GitHub repository PrefectHQ/fastmcp (28,184 stars, last pushed today), licensed Apache-2.0. It adds 27 tokens to every session and 1,099 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 2026-10-22.
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MCP Integration Assistant
Helps design and implement Model Context Protocol (MCP) server integrations for AI agents.
MCP Server Builder
Step-by-step guidance for creating a new MCP server with FastMCP or the TypeScript SDK — tool definitions, resource handlers, error responses, and usage examples.
cor-auth
Authentication cheat sheet for the COR MCP Server — covers both auth modes (email/password and client credentials) step by step, token refresh mechanism, and common auth errors.