Skills or MCP servers: which to pick, and when to use both
What a skill does, what an MCP server does, how much context each costs, their risks, and how to combine them in one project.
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A skill and an MCP server do different jobs. The skill teaches your agent a method; the MCP server gives it access to an outside system. They are often compared, but they complement each other.
What each one does
A skill is a folder with a SKILL.md file: instructions, and sometimes templates, examples or reference files. It is written know-how that the agent follows. The format is an open standard, Agent Skills, adopted by many agents.
An MCP server exposes tools, data and workflows to the agent. The Model Context Protocol is an open standard for connecting an AI application to external systems: local files, databases, search engines, online services. In Claude Code you add one with claude mcp add, over HTTP for a remote service or over stdio for a process that runs on your machine.
A concrete example: a skill describes how to write a bug report following your team's rules. An MCP server connected to your ticket tracker lets the agent read the ticket and write the report into it.
Context cost
Both load in stages, but not in the same way.
- Skill. At startup the agent reads only each skill's name and description. The full
SKILL.mdenters context only when your request matches. Once loaded, it stays in context for the session, so every line is a recurring cost. In Claude Code, the skill listing has a character budget that scales with the context window, and each description is truncated at 1,536 characters. - MCP server. In Claude Code, tool search defers loading definitions: at startup only tool names and server instructions are loaded. The cost comes mostly from the results. Claude Code shows a warning when a tool's output exceeds 10,000 tokens and caps it at 25,000 by default, adjustable with the
MAX_MCP_OUTPUT_TOKENSvariable.
Other agents may load MCP tools differently: check your agent's documentation.
Security
Skill. Installing a skill means copying files, and you can read all of them first. Two points to watch, according to the Claude Code documentation: a skill can include scripts, and its allowed-tools field lets listed tools run without asking you during the turn where the skill is invoked. A skill committed to a repository can therefore grant itself broad access, so review it before opening an unfamiliar project. The details are in Using resources safely.
MCP server. A stdio server runs on your machine; an HTTP server sends your requests to a third party. The Claude Code documentation asks you to verify that you trust each server before connecting it, and notes that servers that fetch external content can expose you to prompt injection. A project-scoped server is stored in .mcp.json and shared with the team through version control: read it before you accept.
Comparison table
| Criterion | Skill | MCP server |
|---|---|---|
| Provides | A method, templates, examples | External tools and data |
| Form | A folder with SKILL.md | A local process or a remote service |
| Loading | Description at start, content on demand | Tool names at start (Claude Code), definitions on demand |
| Main cost | The skill text, once loaded | The results the tools return |
| Reaches the outside world | No, except through scripts or other tools | Yes, that is its purpose |
| Risk to watch | Scripts and rights granted by allowed-tools | Trust in the server, prompt injection |
| Setup | Copy files | Configure the server, sometimes authenticate |
When to use one, the other, or both
- Skill alone: a way of working you want repeated (audit, writing guide, deliverable format), with no external data.
- MCP alone: raw access to a system, with no particular guidance on how to use it.
- Both: the tool provides access, the skill says how to use it. For example, an MCP server pointing at your database and a skill that describes your query conventions and the report format you expect. The skill keeps the agent from improvising with the tool.
To start, browse the skills catalog and follow Install your first resource.
Sources
Frequently asked questions
Can a skill replace an MCP server?
Only if the task needs no external data or service. A skill describes how to do something; an MCP server gives access to a system (database, API, tool). To read your tickets or query a database, the agent needs access, so it needs a tool.
Does an MCP server weigh down every conversation?
Less than it used to: in Claude Code, tool search loads only tool names and server instructions at the start, and full definitions arrive when Claude needs them. Very large results are still a real cost.
Which one is safer?
Neither is neutral. A skill is a folder of files you can read before installing. An MCP server can run as a local process or be remote, and a server that fetches external content exposes you to prompt injection. Review both.