MCP Server Primitives: Resources

Resources are one of the Model Context Protocol's (MCP) three server primitives, representing data that a server exposes for an agent to read, such as files, database records, API responses, or live system state, identified by URIs that the agent or client retrieves on demand. Unlike tools, which perform actions, resources are passive data sources that let agents dynamically discover and pull in relevant information rather than requiring everything pre-loaded into the initial context. This primitive addresses the context engineering problem at the protocol level: instead of stuffing everything into a system prompt, a developer exposes resources that the agent requests as needed, keeping the context window focused on what actually matters.