Defining resources

Overview

• Resources allow MCP servers to expose data to clients
• Define one resource for each distinct read operation
• Accessed through the MCP client via read resource requests

Resource Types

Direct (Static) Resources

• Have a static URI that never changes
• Example: docs://documents
• Same format every time

Templated Resources

• Contain one or more parameters in the URI
• Example: docs://documents/{doc_id}
• Parameters are automatically parsed by Python MCP SDK and provided as keyword arguments to functions
• Keyword argument names match the parameter names in the URI

Implementation Details

Decorator Syntax

• Use @mcp. resource() decorator
• First argument: URI (the resource address/route)
• Second argument: mime_type (hints to client about data format)
• application/json for structured JSON data
• text/plain for plain text content

MIME Types

• Tells the client what type of data is being returned
• Client uses this to determine how to deserialize the data
• Examples: application/json, text/plain, binary data

Function Return Values

• Return native Python data types (lists, strings, dictionaries)
• Python MCP SDK automatically serializes to string format
• No need to manually convert to JSON or other formats

Practical Example: Document System

Resource 1 (Direct): List all documents

• URI: docs://documents
• MIME type: application/json
• Returns: list of document names/IDs

Resource 2 (Templated): Fetch single document

• URI: docs://documents/{doc_id}
• MIME type: text/plain
• Returns: document contents as string
• Includes error handling for non-existent documents

Testing

• Use MCP Inspector to test resources
• List direct resources separately from templated resources
• Verify returned data structure and MIME type

Takeaways

• Resources expose data to MCP clients through static or templated URIs, with one resource per distinct read operation
• Templated resources use parameters in the URI (e. g. , docs://documents/{doc_id}) that are automatically parsed and passed as keyword arguments to handler functions
• Use the @mcp. resource() decorator with a URI and mime_type argument to define resources; the SDK automatically serializes Python return values to strings
• MIME types (application/json, text/plain, etc. ) tell clients how to deserialize the returned data
• Test resources with MCP Inspector to verify data structure and MIME type correctness