What is an MCP Server?
A service exposing capabilities to AI agents via the Model Context Protocol — tools, resources, and prompts that any MCP-compatible agent can discover and use. MCP servers are the capability providers in the MCP architecture.
WHY IT MATTERS
MCP servers package functionality into standard interfaces. Like web servers serving content to browsers, MCP servers serve capabilities to agents — database queries, calendar integration, code execution, file operations, and more.
Servers declare their capabilities through manifests that describe available tools (with JSON Schema parameters), resources (with URI addressing), and prompts (with parameter templates). Clients browse these declarations before invoking anything.
Composability is a key strength — agents connect to multiple servers simultaneously, combining capabilities into complex workflows. A coding agent might connect to a GitHub server, a file system server, and a database server all at once.
HOW POLICYLAYER USES THIS
PolicyLayer sits between the MCP client and any MCP server as a transparent proxy. The server requires no modifications — PolicyLayer intercepts tool calls before they reach the server and evaluates them against YAML policies. The server sees normal MCP requests; the client sees normal MCP responses. PolicyLayer enforces the rules in between.
IN THE CATALOGUE
PolicyLayer continuously scans the MCP ecosystem and classifies every tool it finds by risk category.