If you have spent any time building on Claude lately, you have run into the same fork in the road. Something needs to work better, and there are now two obvious ways to fix it. Write a Skill, or stand up an MCP server.
The two get discussed as rivals, which is the wrong frame and leads people to build the wrong thing. They are not competing implementations of the same idea. They solve genuinely different problems, and the difference is easy to state once you see it.
A Skill changes what Claude knows. An MCP server changes what Claude can reach.
Everything else follows from that. Here is how each one works, the test I use to decide, and why the strongest setups end up using both.
- Skills package expertise. A folder with a SKILL.md file of instructions, plus optional scripts and reference files. No server, no network.
- MCP packages capability. A running server that exposes tools and data, so Claude can query live systems and take real actions.
- The deciding test: does Claude need to know something, or does it need to reach something? Knowledge is a Skill. Reach is MCP.
- They compose. The server provides the tools, the Skill teaches Claude when and how to use them well.
- Skills are far cheaper to build. A useful one is a markdown file. An MCP server is software you have to host and maintain.
What a Claude Skill actually is
A Skill is a folder. At minimum it contains a file called SKILL.md, which holds a name, a description, and a body of instructions written in plain markdown. It can also carry scripts, templates, reference documents, or example files that Claude can open when it needs them.
The clever part is how Claude loads it. Only the name and description sit in context at first, costing you almost nothing. When a task looks like it matches that description, Claude pulls in the full body. If the Skill points at extra files, those get read only when they become relevant.
That progressive loading is why you can install a lot of Skills without drowning your context window. The metadata is tiny, and the expensive content is fetched on demand.
What a Skill cannot do is go and get anything. It has no network access of its own and no connection to your systems. It is knowledge, expressed as instructions, sitting on disk waiting to be relevant.
Good Skill candidates: your team’s code review conventions. The exact structure your reports must follow. A brand voice guide. A multi-step process that Claude keeps doing in a slightly different order every time. The tribal knowledge that currently lives in one person’s head and gets re-explained weekly.
What an MCP server actually is
An MCP server is a program that runs, either locally over stdio or remotely over HTTP. It advertises a set of tools to any MCP client, and when Claude calls one, real code executes and returns real data.
That is the categorical difference. A Skill cannot tell you today’s search rankings, because it is a text file. An MCP server can, because it makes a live API call when asked.
MCP also handles the parts that get awkward fast: authentication, rate limiting, structured inputs and outputs, and errors. Because it is an open protocol, one server works across Claude, Cursor, Windsurf, VS Code, and every other compliant client, so you build the integration once.
Good MCP candidates: anything behind an API or a login. Live data that changes. Your database. Your ticketing system. Actions with side effects, like sending an email or deploying a build. Anything where the answer depends on the state of the world right now.
For a concrete example I can speak to directly, the tools I build are MCP servers precisely because they have to be. ContextBolt SEO returns live keyword volumes, difficulty scores, and SERP positions, and none of that can live in a markdown file because it changes daily. Same for the bookmarks server, which searches a library that grows every time you save something.
Claude Skills vs MCP side by side
| Dimension | Claude Skills | MCP servers |
|---|---|---|
| What it provides | Knowledge and procedure | Data access and actions |
| Form | A folder with SKILL.md | A running server process |
| Live external data | No | Yes |
| Can take real actions | Via bundled scripts only | Yes |
| Authentication handling | Not applicable | Built in |
| Build effort | Minutes, write markdown | Days, plus hosting |
| Ongoing maintenance | Edit a file | Uptime, versions, keys |
| Context cost | Tiny until invoked | Tool definitions always loaded |
| Portable across clients | Claude ecosystem | Any MCP client |
| Works offline | Yes | Depends on the service |
The one question that decides it
When someone asks me which to build, I ask one thing back. Where does the missing piece live?
If it lives in someone’s head, in a wiki, in a style guide, or in a process nobody wrote down, that is a Skill. The information already exists. Claude just needs it present and needs to follow it the same way every time.
If it lives in a database, an API, a SaaS product, or anywhere with an access token, that is MCP. No amount of instruction gets Claude to data it cannot reach.
Two follow-ups usually settle the remaining cases.
Does the answer change without anyone editing anything? Live rankings, open tickets, yesterday’s revenue. If yes, it is MCP, because a static file goes stale the moment you write it.
Would a competent new hire be able to do this from a written document? If yes, it is a Skill. That document is the Skill.
How Skills and MCP work together
This is the part that gets missed, and it is where most of the real value sits.
An MCP server hands Claude a set of tools with descriptions. That tells Claude what each tool does. It does not tell Claude which tool to reach for in a given situation, what order to call them in, or how to read the results in your particular context.
A Skill fills exactly that gap.
Take a concrete case. An SEO MCP server might expose tools for keyword research, difficulty scoring, SERP inspection, and backlink lookups. Given a vague request like “should we write about this topic”, Claude will do something reasonable, but it will do something slightly different each time.
Now add a Skill that says: check volume first, discard anything under 50 searches a month, pull the SERP and count how many results are forum threads, look up the referring domains of the top three, and only recommend the topic if our own domain has at least half that many. Same tools, same server. But now it is a repeatable process with your judgment baked in, and the output is consistent enough to act on.
The general pattern is MCP for reach and Skills for judgment. The server can do a hundred things. The Skill encodes which five matter to you and in what order.
Common mistakes on both sides
Building an MCP server for static information: if the content does not change and needs no authentication, you have built a server to serve a text file. A Skill does this with no hosting and no uptime worry.
Writing a Skill that needs live data: instructions cannot fetch. If your Skill says “look up the current price”, it will either hallucinate a number or tell you it cannot. Add the tool.
Treating them as competitors: the choice is rarely either-or. Most mature setups have a small number of MCP servers for reach and several Skills for procedure.
Overstuffing one Skill: a Skill covering five unrelated jobs triggers at the wrong moments and pollutes context. Split by task, keep descriptions specific, and let the matching work properly.
Forgetting MCP tool definitions cost context permanently: unlike a Skill’s body, every connected server’s tool list sits in context for the whole conversation. Ten servers with a dozen tools each is a real tax. Connect what you use.
Start with a Skill, add MCP when you hit the wall
If you are genuinely unsure, write the Skill. It takes an afternoon at most, costs nothing to host, and you will learn precisely where it falls short.
That failure point is informative. The moment your Skill wants a number it cannot get, or an action it cannot take, you have found the boundary and you know exactly which MCP tool you need. You will build a much better server for having hit the wall first, because you will build the two tools the workflow actually needs instead of the twelve you imagined.
The reverse order wastes more time. People start by building a server, expose everything the API offers, then discover Claude uses three endpoints and needs guidance rather than more surface area.
Skill first, then reach. It is the cheaper way round, and it usually produces a smaller and better-designed server at the end of it.