Tools, Resources and Prompts

Who decides what runs

Tools are functions the model can choose to call (model-controlled), such as "create issue". Resources are read-only data the application can attach, such as a file or a database row (application-controlled). Prompts are reusable templates the user picks, such as a slash command (user-controlled). Choosing the right primitive keeps control where it belongs.

Comparing the three

Use a tool when an action or computation is needed, a resource when you only supply data, and a prompt when the user triggers a ready-made workflow.

Primitive   Controlled by   Example
Tool        the model       create_issue(title, body)
Resource    the app         file:///reports/q3.csv
Prompt      the user        /review-pull-request

Do not make everything a tool

Too many tools confuse the model and use context. Expose static reference data as resources, and keep each tool small and clearly named.

Quick check: Which MCP primitive is chosen by the user, like a slash command?

• Tool
• Resource
• Prompt
• Transport