MCP Server Primitives: Tools

Tools are one of the Model Context Protocol's (MCP) three server primitives, representing executable actions that an agent can discover and invoke through the protocol, such as querying a database, creating a file, sending a message, or triggering a deployment. Each tool carries a name, description, and JSON Schema for its input parameters, following the same patterns as native function calling but standardized across MCP so any conforming client can use any conforming server's tools. Tools are the primary mechanism by which agents affect the external world through the protocol layer, which makes tool design decisions, including naming, scope, and error handling, directly determine how reliably agents can complete real tasks.