Defining resources

MCP Resources: Document Mention Feature

Goal: Implement a feature allowing users to mention documents (e. g. , @report. pdf) to automatically fetch and insert the document's content into the prompt sent to the LLM (Claude).

Core Components:

• Two Features:
• Autocomplete: When the user types @, the MCP server must provide a list of all available document names.
• Content Fetching: When the user submits the message, the MCP server must retrieve the content of the mentioned document.
• Mechanism: The MCP server uses Resources to expose specific data and read operations to the client.

Resource Definitions:

• Purpose: Define one resource for each distinct read operation.
• Required Resources:
• A resource to return a list of all document names (for autocomplete).
• A resource to return the content of a single document based on its ID.

Resource Types:

• Direct (Static) Resources:
• Have a fixed, unchanging URI (e. g. , docs://documents).
• Used for operations that do not require user input parameters.
• Templated Resources:
• Contain one or more parameters/wildcards in the URI (e. g. , docs://documents/{doc_id}).
• The MCP SDK automatically parses these parameters and passes them as keyword arguments to the associated function.
• Used when customization or selection is needed (e. g. , fetching a specific document).

Client-Server Interaction Flow (Autocomplete Example):

• User types @ in the client.
• Client → MCP Client sends a Read Resource Request.
• The request includes the specific URI defined for the resource.
• MCP Server uses the URI to locate and execute the corresponding function.
• Server returns a Read Resource Result message to the client.
• Client displays the returned data (e. g. , the list of document names) in the autocomplete window.

Implementation Details (Code Structure):

• List Documents Resource (Static):
• URI: docs://documents
• MIME Type: application/json (Indicates structured data).
• Function returns: A list of strings (document IDs/names).
• Fetch Document Resource (Templated):
• URI: docs://documents/{doc_id}
• MIME Type: text/plain (Indicates raw, unstructured text content).
• Function receives: doc_id as a keyword argument.
• Function returns: The string content of the requested document.

Takeaways

• The document mention feature relies on MCP Resources to perform two core functions: providing a list of available document names (autocomplete) and retrieving the content of a specific document.
• Resources are defined as either Direct (Static) or Templated, where Templated resources use parameters (like {doc_id}) to allow for dynamic data retrieval.
• The client initiates the process by sending a Read Resource Request containing the specific URI to the MCP server, which then executes the corresponding function.
• A static resource (e. g. , docs://documents) is used to return a list of all document IDs, while a templated resource (e. g. , docs://documents/{doc_id}) is used to fetch the raw text content of a single document.