MCP review

Tools

• Control: Model controlled
• Who decides: Claude alone decides when to run a tool
• Purpose: Add capabilities to Claude
• Use case: When you need the model to execute actions (e. g. , JavaScript execution, API calls)

Resources

• Control: App controlled
• Who decides: Application code decides when to fetch and use data
• Purpose: Get data into your app for UI display and content rendering
• Use cases:
• Provide autocomplete options in UI
• Augment prompts with fetched data
• List documents from Google Drive for user selection

Prompts

• Control: User controlled
• Who decides: User initiates by clicking buttons, menu options, or slash commands
• Purpose: Implement predefined workflows
• Use case: Pre-written, optimized workflows that users can trigger (e. g. , example buttons in chat interface)

Key Principle

Each primitive serves a different part of the application:

• Tools → serve the model
• Resources → serve the app
• Prompts → serve the users

Use these guidelines to determine which primitive to implement based on your needs.

Takeaways

• Tools give Claude autonomous decision-making power to execute actions; Resources let your app control when to fetch and display data; Prompts let users trigger predefined workflows
• Choose Tools when the model needs to take actions, Resources when you need data for UI/content, and Prompts when users should initiate preset workflows
• Each primitive serves a different stakeholder: Tools serve the model, Resources serve the app, Prompts serve the users