A Skill packages procedural knowledge — instructions, conventions, reusable scripts — that Claude loads when a task matches. MCP exposes live capability — tools, data, and actions in an external system. Most production setups end up using both.
Skills package how, not what.
A Skill is a folder with a SKILL.md file and, optionally, supporting scripts or reference material. It doesn't grant Claude any new ability to reach the outside world — it teaches Claude how to do something well within the tools it already has: a house style for commit messages, a checklist for running an audit, a template for drafting a weekly report.
Skills are model-loaded context, not infrastructure. There's no server to deploy, no auth flow, no uptime to manage. That makes them cheap to write and cheap to iterate on.
MCP grants reach.
MCP servers expose live tools and resources — read a database, call an internal API, send a Slack message, query a CRM. They're the layer that lets Claude act on systems outside the conversation, with real authentication and real side effects.
That comes with the obligations of any service: deployment, secrets management, rate limits, and a security boundary around what the tool is allowed to touch.
The test: does Claude need new knowledge, or a new door?
If the task is "Claude already has the tools, it just needs to do this consistently" — that's a Skill. House style, internal conventions, a multi-step procedure your team already follows by hand.
If the task is "Claude needs to read or write something it currently has no access to" — that's MCP. A live system, a private data source, an action with a side effect outside the conversation.
In our own stack, Skills carry the conventions (how we structure a campaign brief, how we format a client report) and MCP servers carry the access (BossHub, Nexudus, internal Workers). Skills tell Claude how to use the tools well; MCP is what makes the tools exist in the first place.
They compose.
A well-designed Skill often references an MCP tool by name, instructing Claude on the right sequence, the right arguments, and the right judgment calls when using it. The Skill is the playbook; the MCP server is the equipment. Neither replaces the other.
If you're writing instructions, write a Skill. If you're writing a server, you're building MCP. Most mature setups need both, and conflating them is the fastest way to over-engineer a simple need.