// GLOSSARY -- MCP & TOOL INFRASTRUCTURE

What is an MCP Server?

2 min read Updated

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

Intercept sits between the MCP client and any MCP server as a transparent proxy. The server requires no modifications — Intercept 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. Intercept enforces the rules in between.

FREQUENTLY ASKED QUESTIONS

How does Intercept work with existing MCP servers?
No changes to the server are needed. Intercept acts as a transparent proxy — you configure the client to connect to Intercept, and Intercept forwards approved requests to the upstream server. The server is unaware that a policy layer exists.
Can I use Intercept with multiple MCP servers?
Yes. Intercept can proxy connections to multiple upstream MCP servers, applying different YAML policy files to each. This lets you enforce distinct policy rules per server.
Can I build custom MCP servers?
Yes — MCP is open and well-documented. Custom servers can expose any functionality. Intercept will enforce policies on tool calls to your custom server just as it does for any other.

FURTHER READING

Enforce policies on every tool call

Intercept is the open-source MCP proxy that enforces YAML policies on AI agent tool calls. No code changes needed.

npx -y @policylayer/intercept
github.com/policylayer/intercept →
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