MCP and Interoperability

One protocol instead of N integrations

The Model Context Protocol (MCP) is an open standard for connecting AI clients to external tools and data. Before it, every AI app needed a custom integration for every tool. With it, a server describes its tools once and any compliant client can use them. In practice: one MCP server works with Claude Desktop, Claude Code, Cowork, Codex, and other clients without custom code per client.

The roles are simple. An MCP server and client exposes tools; an MCP client is the AI application that connects, lists the tools, and calls them during a conversation or agent run. A tool is one named operation with typed inputs and outputs. In practice: the client asks the server what it can do, then invokes tools by name with structured arguments.

Granting access safely

Connecting an agent to your data raises an obvious question: what exactly did you just hand over? OAuth for agents answers it with a consent flow that issues a scoped, expiring, revocable token instead of a raw key. The API-key contrast matters: a raw key usually carries full account power and only dies by rotation. In practice: with OAuth you approve exactly what the agent may touch and can revoke it without breaking anything else.

Structured outputs make tool results dependable: the response is constrained to a defined schema, such as JSON with required fields, so downstream code either gets the shape it expects or fails loudly. In practice: a tool that must return a score and a flag list cannot silently drift into prose.

The Cromus Lens

Cromus hosts an MCP server at mcp.cromus.ai exposing fifteen deterministic tools: score_skill, simulate_cost, score_graph, simulate_graph_cost, validate_skill, validate_ethos, validate_memory, validate_agents, validate_mcp_deps, check_mcp_drift, check_model_drift, check_usage_waste, check_policy, reality_check_summary, and get_approved_skill. They produce reproducible results from their inputs; they do not use an LLM to make the check. Tool access is governed by the authenticated credential and scope; get_approved_skill retrieves approved Sync Center revisions and remains subject to its product access rules. Any compatible client can discover the server's available tools. The point for learners: interoperability lets the same reviewable checks travel with the agent.

The panel below gives you a copyable connect snippet for the Cromus MCP server. It is an honest connect exercise — pasting the snippet configures your client against the real endpoint; it does not run any tool or mutate anything on its own.