Using Prompts and Resources Efficiently

MCP has three primitives: Tools, Resources, and Prompts. While Tools get all the attention, Resources and Prompts serve distinct purposes that are often misunderstood.

The Three Primitives

Primitive	Control	Purpose	Client Support
Tools	Agent-driven	Actions with side effects	✅ Widely supported
Resources	User-driven	Read-only data attachments	⚠️ Limited support
Prompts	User or Agent	Instructions/templates	⚠️ Limited support

Resources and Prompts require client-side support. Not all MCP clients implement them. Tools are universally supported because they’re handled by LLM providers (Anthropic, OpenAI).

Resources: User-Controlled Data

What Are Resources?

Resources are read-only data that users can attach to their input. Key points:

User decides — not the agent
Agent cannot access resources directly — it must use Tools
Tools control access — authentication, scopes, permissions

Real-World Examples

The best example is the @ command in Cursor, Windsurf, and Android Studio:

Client	@ Command	What It Attaches
Cursor	`@file.ts`	File contents
Windsurf	`@PR #123`	Pull request diff
Android Studio	`@build.gradle`	Build configuration

When you type @file.ts, you’re adding a resource to your prompt. The user explicitly chooses what context to include.

When to Use Resources

import { Resource } from 'leanmcp';

@Resource({ description: "Current user's profile" })
async userProfile() {
  return {
    name: "John Doe",
    role: "Developer",
    preferences: { theme: "dark", language: "en" }
  };
}

@Resource({ description: "Project configuration" })
async projectConfig() {
  return {
    name: "my-app",
    version: "1.0.0",
    dependencies: { ... }
  };
}

Use resources for:

Configuration files
User profiles
Project metadata
Any read-only context users might want to attach

Resources are not for data the agent should fetch on its own. That’s what Tools are for.

Prompts: Instructions for Agents

What Are Prompts?

Prompts are instructions that tell the agent how to behave. They can be:

User-added — Explicitly attached by the user
Agent-picked — Agent selects relevant prompts when needed

Real-World Examples

The best example is Guidelines in Cursor and Windsurf:

Client	Feature	Purpose
Cursor	`.cursorrules`	Project-specific coding guidelines
Windsurf	`.windsurfrules`	Project-specific behavior
Both	Guidelines panel	Agent instructions

These are prompts — instructions that shape how the agent generates code.

When to Use Prompts

import { Prompt } from 'leanmcp';

@Prompt({ description: "Code review guidelines" })
codeReviewPrompt() {
  return {
    messages: [{
      role: "user",
      content: {
        type: "text",
        text: `You are a senior code reviewer. Follow these rules:
1. Check for security vulnerabilities
2. Ensure proper error handling
3. Verify edge cases are covered
4. Suggest performance improvements
5. Keep feedback constructive`
      }
    }]
  };
}

@Prompt({ description: "API documentation writer" })
apiDocPrompt() {
  return {
    messages: [{
      role: "user",
      content: {
        type: "text",
        text: `Generate API documentation with:
- Clear endpoint descriptions
- Request/response examples
- Error codes and meanings
- Authentication requirements`
      }
    }]
  };
}

Use prompts for:

Coding standards
Review guidelines
Documentation templates
Any reusable instructions

Tools vs Resources vs Prompts

Question	Answer
Who decides to use it?	Tools: Agent / Resources: User / Prompts: Both
Can it modify data?	Tools: Yes / Resources: No / Prompts: No
Needs client support?	Tools: No (LLM handles) / Resources: Yes / Prompts: Yes
Purpose?	Tools: Actions / Resources: Context / Prompts: Instructions

Client Support Reality

The hard truth: Most MCP clients only support Tools.

Client	Tools	Resources	Prompts
Claude Desktop	✅	✅	✅
Cursor	✅	✅ (@ files)	✅ (rules)
Windsurf	✅	✅ (@ files)	✅ (rules)
ChatGPT	✅	❌	❌
Custom clients	✅	Varies	Varies

If your MCP needs broad client support, focus on Tools. Use Resources and Prompts as progressive enhancements for clients that support them.

Best Practices

For Resources

Keep them read-only — Resources should never modify state
Make them user-relevant — Only expose what users would want to attach
Provide fallbacks — If resources aren’t supported, expose similar data via Tools

// Resource for clients that support it
@Resource({ description: "Project config" })
async projectConfig() {
  return await this.getConfig();
}

// Tool fallback for clients that don't
@Tool({ description: "Get project config" })
async getProjectConfig() {
  return await this.getConfig();
}

For Prompts

Keep them focused — One prompt per behavior/task
Make them reusable — Generic enough for multiple contexts
Don’t duplicate — If it’s in the prompt, don’t repeat in tool descriptions

// ❌ BAD: Overly specific
@Prompt({ description: "Review React TypeScript code on Monday" })

// ✅ GOOD: Reusable
@Prompt({ description: "Code review guidelines" })

Summary

Primitive	Control	Best For	Client Support
Tools	Agent	Actions, data access, auth	✅ Universal
Resources	User	Config, profiles, context	⚠️ Limited
Prompts	Both	Instructions, guidelines	⚠️ Limited

Key insight: Tools are LLM-focused (agent-driven). Resources and Prompts are UI-focused (user-driven). Build for Tools first, enhance with Resources/Prompts for supporting clients.

Tools Deep Dive

Learn about MCP tools

Resources Guide

Understanding resources

Welcome

CLI

Deployment

Best Practices

Platform Features

Security

Comparisons

Examples

Using Prompts and Resources Efficiently

The Three Primitives

Resources: User-Controlled Data

What Are Resources?

Real-World Examples

When to Use Resources

Prompts: Instructions for Agents

What Are Prompts?

Real-World Examples

When to Use Prompts

Tools vs Resources vs Prompts

Client Support Reality

Best Practices

For Resources

For Prompts

Summary

Tools Deep Dive

Resources Guide

​The Three Primitives

​Resources: User-Controlled Data

​What Are Resources?

​Real-World Examples

​When to Use Resources

​Prompts: Instructions for Agents

​What Are Prompts?

​Real-World Examples

​When to Use Prompts

​Tools vs Resources vs Prompts

​Client Support Reality

​Best Practices

​For Resources

​For Prompts

​Summary

Tools Deep Dive

Resources Guide

The Three Primitives

Resources: User-Controlled Data

What Are Resources?

Real-World Examples

When to Use Resources

Prompts: Instructions for Agents

What Are Prompts?

Real-World Examples

When to Use Prompts

Tools vs Resources vs Prompts

Client Support Reality

Best Practices

For Resources

For Prompts

Summary