MCP Budget Enforcement: A Practical Guide to Controlling AI Tool Spend

MCP (Model Context Protocol) is becoming the standard way AI agents interact with tools. But MCP has no built-in concept of cost. A tools/call request to a cheap lookup function and a $2 code execution tool look identical at the protocol level. This guide shows how to add economic governance to any MCP server. The Problem with Unmetered MCP When you connect an AI agent to MCP servers, the agent can call any tool it has access to, as many times as it wants. There's no protocol-level mechanism for: Assigning costs to different tool calls Tracking cumulative spend per agent Enforcing a budget ceiling Attributing costs to teams or departments Delegating budget from a parent agent to sub-agents Most MCP gateways solve the connectivity problem — routing, auth, discovery. But connectivity without cost control is like an open highway with no toll booths. Step 1: Define Per-Tool Costs Map tool calls to costs with a cost profile: mcp : costProfile : defaultCostCredits : 1 tools : - name : " web_