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 URI every time it's accessed

Templated Resources

• Contain one or more parameters in the URI
• Example: docs://documents/{doc_id}
• Parameters are automatically parsed by the Python MCP SDK
• Parameter names become keyword arguments in the handler function
• Allow customization and variety in what clients can request

Implementation Flow

• Client types trigger a read resource request
• Request includes a URI (the "address" of the resource)
• MCP server receives request, matches URI to handler function
• Server executes function and returns result in read resource result message
• Client receives data and uses it (e. g. , display in autocomplete)

Defining Resources in Python MCP SDK

Decorator Syntax

• Use @mcp. resource() decorator
• First argument: URI string
• Second argument: MIME type (hints to client about data format)

MIME Types

• application/json - for structured JSON data
• text/plain - for plain text content
• SDK automatically serializes return values to strings

Function Parameters

• Templated resource parameters automatically become keyword arguments
• Parameter name in URI matches the function argument name
• Example: {doc_id} in URI → doc_id parameter in function

Practical Example

• List documents resource: Direct resource returning all available document names for autocomplete
• Fetch document resource: Templated resource returning contents of a specific document by ID
• Error handling: Validate requested resource exists before returning data

Takeaways

• Resources expose data to clients through URIs; define one resource per distinct read operation
• Resources can be static (fixed URI) or templated (parameterized URI with dynamic values)
• Use @mcp. resource() decorator with URI string and MIME type to define resources in Python MCP SDK
• Templated URI parameters automatically become function keyword arguments (e. g. , {doc_id} → doc_id parameter)
• Client requests trigger server to match URI to handler function, execute it, and return result in appropriate format