MCP Tools and Resources
An MCP server exposes its capabilities through a few defined categories. Learning these categories helps a learner read any MCP server's documentation with confidence, instead of guessing what each listed item actually does.
Tools: Actions the Model Can Trigger
A tool represents something the model can actively do, such as sending a message, creating a record, or running a calculation. Picture a tool as a button on a remote control. Pressing it causes something to happen immediately, out in the real world.
| Tool Example | What Happens |
|---|---|
| send_email | Sends an email to a specified address |
| create_task | Adds a new task to a project board |
| convert_currency | Calculates a currency conversion on demand |
Resources: Data the Model Can Read
A resource represents information the model can pull in without triggering any action. Picture a resource as a book sitting on a shelf, ready to read whenever needed. Reading the book changes nothing about the book itself.
| Resource Example | What It Provides |
|---|---|
| company_handbook | The full text of an internal policy document |
| current_inventory | A live snapshot of stock levels |
| user_profile | Basic account details for the current user |
Prompts: Ready-Made Instructions
Some MCP servers also expose prompts, which are pre-written instruction templates for common tasks. Picture a prompt as a recipe card handed to a cook, laying out the exact steps for a specific dish. The model can use this template instead of writing instructions from scratch every time it faces a similar task.
Three Categories Side by Side
Putting the Three Together
| Category | Everyday Comparison | Changes Anything? |
|---|---|---|
| Tool | Pressing a remote control button | Yes, it triggers an action |
| Resource | Reading a book on a shelf | No, it only provides information |
| Prompt | Following a recipe card | No, it only guides the process |
A Combined Example
A travel assistant reads the "loyalty_status" resource to check a customer's membership tier. It then uses the "book_flight" tool to reserve a seat. Along the way, it follows a "refund_policy" prompt template to explain any cancellation terms clearly. Three separate categories work together inside one smooth conversation.
One Task, Three Categories Working Together
A Second Combined Example
A helpdesk assistant reads a "known_issues" resource to check if a problem is already documented. It then calls a "create_ticket" tool only if the issue is new. This order avoids creating duplicate tickets for problems the support team already knows about, saving time for both the customer and the support staff.
Why This Structure Helps Developers
Clear categories keep an MCP server organized and predictable. A developer building a new server knows exactly where to place each new capability, and a model calling that server knows exactly what kind of behavior to expect from each item it sees, reducing confusion and mistakes on both sides.