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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteMCP defines three server primitives: prompts, which people select and customize; resources, which applications read as context; and tools, which a model can invoke. The response depends on the server and the data it handles. Two official examples make that concrete: an in-memory orders server returns text, JSON resource content, and a completed prompt message, while the filesystem reference server shapes its results according to the file type.
What are the three MCP primitives?
MCP primitives are different ways for a server to make capabilities or context available to a client. Their usual control patterns help distinguish them: people choose prompts, applications manage resources, and models can invoke tools. These are design defaults, not rules that require every MCP client to use one particular interface.
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| Primitive | What it provides | Typical control pattern |
|---|---|---|
| Prompts | Server-provided templates or instructions that can be filled with arguments | User-selected |
| Resources | Content identified by URIs, such as file contents or application data, for use as context | Application-managed |
| Tools | Executable functions that may retrieve information, query APIs, or take actions | Model-invoked |
For tools, the official specification says they are “designed to be model-controlled,” so a model may discover and invoke them based on the conversation. It also recommends a human-visible interface and a way for a person to deny invocations. A tool call is therefore distinct from a resource read or a prompt selection: it asks the server to execute a function.
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MCP defines the protocol envelope and supported forms of content; it does not prescribe one universal answer for every server. A tool result might contain readable text, structured data, image or audio content, or embedded resource content. A resource read or prompt response has its own shape, and the actual values depend on the implementation and the data available to it.
To compare servers, look at which primitives they expose, each tool’s name and input/output schema, the result content type and any structured content, the data or actions the server can reach, and whether you are looking at an example implementation or a deployed service.
What does the in-memory orders server return?
The official TypeScript SDK client guide demonstrates an in-memory SDK example paired with an orders server. Its documented outputs illustrate a tool call, a resource read, and a prompt request; they are not evidence of a separately running order system or live production data.
Rank #2
Tools: names and a text result
The example advertises three tools: lookup-order, order-total, and export-orders. The guide shows lookup-order called with {"id":"A-1041"}. Its result contains one text item: A-1041: 3 items, shipped.
Resource: JSON content
Reading orders://recent returns content labeled application/json, with the order IDs A-1041 and A-1042. This is resource content supplied by that example server, not a standard list of orders that other MCP servers must return.
Rank #3
Prompt: a filled-in message
The prompt named summarize-order takes arguments and returns a user-role text message. With the order ID substituted, the example message is: Write a terse status update for order A-1041. The server supplies the template output; the client presents the prompt for a person to select and customize.
What does the filesystem reference server return?
The official filesystem reference server exposes tools for working with local files, including read_text_file, read_media_file, read_multiple_files, write_file, and list_directory. Its README and implementation document read and mutation operations, their output schemas, and access limited to configured or root-provided allowed directories.
Text files
A text-file read returns a text content block containing the file text, along with structuredContent that has a content field. The text is the file data handled by that server; MCP does not make different servers return identical file contents.
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For image and audio MIME types, media reads return base64 image or audio content blocks. Other binary files are returned as embedded resource content with a URI and MIME type. The response form therefore reflects the kind of file being read rather than always flattening the result into a plain string.
Quick Recap
How should you interpret these server examples?
- They demonstrate concrete protocol response shapes, not universal outputs for every MCP server.
- The orders guide is an in-memory SDK example; the filesystem project is a reference implementation. Neither example establishes the behavior or production readiness of an unrelated deployed service.
- The MCP servers repository describes its maintained servers as demonstrations of protocol features and SDK usage, not production-ready solutions.
- For a real deployment, inspect the server’s declared capabilities and schemas, the permissions and data it can access, and the content blocks it actually constructs.
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