Understanding MCP servers changeddocs/2025-03-26/learn/server-concepts
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99Servers provide functionality through three building blocks:
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11| Feature | Explanation | Examples | Who controls it |
12| ------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------ | --------------- |
13| **Tools** | Functions that your LLM can actively call, and decides when to use them based on user requests. Tools can write to databases, call external APIs, modify files, or trigger other logic. | Search flights<br />Send messages<br />Create calendar events | Model |
14| **Resources** | Passive data sources that provide read-only access to information for context, such as file contents, database schemas, or API documentation. | Retrieve documents<br />Access knowledge bases<br />Read calendars | Application |
15| **Prompts** | Pre-built instruction templates that tell the model to work with specific tools and resources. | Plan a vacation<br />Summarize my meetings<br />Draft an email | User |
11| Feature | Explanation | Examples | Who controls it |
12| - | - | - | - |
13| **Tools** | Functions that your LLM can actively call, and decides when to use them based on user requests. Tools can write to databases, call external APIs, modify files, or trigger other logic. | Search flights<br />Send messages<br />Create calendar events | Model |
14| **Resources** | Passive data sources that provide read-only access to information for context, such as file contents, database schemas, or API documentation. | Retrieve documents<br />Access knowledge bases<br />Read calendars | Application |
15| **Prompts** | Pre-built instruction templates that tell the model to work with specific tools and resources. | Plan a vacation<br />Summarize my meetings<br />Draft an email | User |
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1717We will use a hypothetical scenario to demonstrate the role of each of these features, and show how they can work together.
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2626
2727**Protocol operations:**
2828
29| Method | Purpose | Returns |
30| ------------ | ------------------------ | -------------------------------------- |
29| Method | Purpose | Returns |
30| - | - | - |
3131| `tools/list` | Discover available tools | Array of tool definitions with schemas |
32| `tools/call` | Execute a specific tool | Tool execution result |
32| `tools/call` | Execute a specific tool | Tool execution result |
3333
3434**Example tool definition:**
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109109
110110**Protocol operations:**
111111
112| Method | Purpose | Returns |
113| -------------------------- | ------------------------------- | -------------------------------------- |
114| `resources/list` | List available direct resources | Array of resource descriptors |
115| `resources/templates/list` | Discover resource templates | Array of resource template definitions |
116| `resources/read` | Retrieve resource contents | Resource data with metadata |
117| `resources/subscribe` | Monitor resource changes | Subscription confirmation |
112| Method | Purpose | Returns |
113| - | - | - |
114| `resources/list` | List available direct resources | Array of resource descriptors |
115| `resources/templates/list` | Discover resource templates | Array of resource template definitions |
116| `resources/read` | Retrieve resource contents | Resource data with metadata |
117| `resources/subscribe` | Monitor resource changes | Subscription confirmation |
118118
119119#### Example: Getting Travel Planning Context
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180180
181181**Protocol operations:**
182182
183| Method | Purpose | Returns |
184| -------------- | -------------------------- | ------------------------------------- |
185| `prompts/list` | Discover available prompts | Array of prompt descriptors |
186| `prompts/get` | Retrieve prompt details | Full prompt definition with arguments |
183| Method | Purpose | Returns |
184| - | - | - |
185| `prompts/list` | Discover available prompts | Array of prompt descriptors |
186| `prompts/get` | Retrieve prompt details | Full prompt definition with arguments |
187187
188188#### Example: Streamlined Workflows
189189
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