Claude Code, MCP Servers, and Cursor Rules: What These AI Coding Tools Actually Do
These three file types keep showing up in "AI developer tooling" listings. Here's what each one actually configures, in plain terms.
Why this category exists now
AI coding assistants — Claude Code, Cursor, and similar tools — became genuinely useful once they could be configured for a specific codebase or workflow instead of starting from a blank slate every session. That configuration takes a few standard forms now, and each one is different enough that it's worth knowing what you're actually buying when you see it listed.
MCP servers: giving an AI model access to real tools and data
The Model Context Protocol (MCP) is an open standard, introduced by Anthropic, for connecting an AI application to external tools and data sources in a consistent way — described in Anthropic's own materials as similar to what USB-C did for hardware: one standard connector instead of a custom integration for every pairing of AI app and external system. An MCP server exposes a specific set of tools (read this database, search this internal wiki, query this API) that a client application like Claude Code or Claude Desktop can then use directly, instead of a person copy-pasting data back and forth by hand. A pre-built MCP server config, sold as a template, saves the real engineering work of building and testing that integration yourself.
SKILL.md files: packaged, reusable instructions for Claude
A SKILL.md file is a structured instruction set that tells Claude how to approach a specific, recurring type of task — the equivalent of writing a very good, tested prompt once and packaging it so it loads automatically whenever it's relevant, instead of re-explaining the same context every session. A well-built skill file encodes real hard-won detail: which edge cases to check, which output format to use, which mistakes to avoid — the kind of institutional knowledge that otherwise lives only in one person's head.
Cursor / Windsurf rules files: persistent context for a codebase
A rules file tells an AI coding assistant the standing facts about a project that would otherwise need repeating in every prompt: the tech stack, the naming conventions, which patterns are banned, how tests are structured. Without one, every session starts from zero context and the assistant has to be told the same things repeatedly. With a good one, suggestions match the codebase's actual conventions from the first message.
What to actually check before buying one
These are text files, not compiled software, so quality varies enormously and isn't visible from a screenshot. Before buying an MCP server config, a SKILL.md file, or a rules file, check: does the listing show the actual file content or a real example of it in use, does it document exactly which tools/permissions it grants (for MCP servers, this matters for security), and is there a changelog or version note — these tools are unusually current-events-sensitive, since both Anthropic's and Cursor's own conventions have shifted more than once. A file written against an outdated convention can silently do nothing.
Source: Anthropic — "Introducing the Model Context Protocol".