0:01Last time we followed one request through this picture, the host decides what's connected, and its MCP client does the asking.
0:08So when the assistant needs a file, the request crosses over, and the server sends the answer back.
0:13But so far this server is a black box to us, it answers, and that's all we know.
0:18Time to open it up and see what's inside.
0:21Now we can see inside, and there's room for three kinds of things.
0:25The first kind is a tool, something the server can do on request.
0:29This server has two, one searches a folder, and the other reads a file.
0:33When the model decides it needs a file found, the client sends the request over, the server runs the tool, and the result comes back.
0:41That's what makes a tool a tool, it does something, and it's the model that chooses when.
0:46So that's the first of the three.
0:48Not everything our app wants is an action, though. Sometimes it just needs to know what's in there.
0:53So the second kind is a resource, a piece of data with its own address.
0:58On this server, that's the contents of a file, or the listing of a folder.
1:02A read makes the same round trip, a request over, an answer back. The difference is that nothing changed. The server looked up the data and returned it.
1:10And that's two of the three.
1:12There's one kind left, and it isn't for the model or for the app. It's for you.
1:17A prompt is a request written in advance by whoever built the server.
1:21This server ships one that summarizes a folder, a whole request, worded once, ready to reuse.
1:27You pick it when you need it, the host fills in the details, and the complete request goes out, no typing it from scratch.
1:33If the three kinds still feel abstract, don't worry, we'll look at each one in more detail as the series goes on.
1:39One thing to clarify, though, the server just offers these things. It's up to the host app to ask for what it needs.
1:47That's the relationship. A server is a list of things on offer, and every request starts with the host.
1:52Next time we'll take a server somebody's already built, connect it to a host, and watch all of this show up live.

Tools, Resources, and Prompts

Created by Abhyuday DesaiPublished 2 Oct, v1Runs 2 min 4 sec

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About this video

In Episode 04 of MCP Explained, we open up a server and look at the three kinds of things it can offer. A tool is something the server does on request, and the model chooses when. A resource is a piece of data with its own address, read by the app. A prompt is a request written in advance by whoever built the server, picked by you. The server offers; the host asks.

You'll learn how to:

See what makes a tool a tool: it does something, and the model decides when to call it
Understand a resource as data with an address, and why reading one changes nothing on the server
Learn what a prompt is for, who picks it, and how the host fills in the details
Keep the one rule that organizes all three: the server offers these things, and every request starts with the host

This video is for developers hearing about MCP for the first time. No prior MCP knowledge is needed.

What changed

v102 Oct 2026abhydesai2 min 4 sec805b43c

First published version.

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