MCP tools vs resources — CCA-F Exam Prep

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REAL STORY A developer staring at their MCP server code. On screen: a tool called 'get_customer_profile' that fetches data but doesn't change anything. Next to it, a tool called 'send_invoice' that sends a real invoice. Both are registered as 'tools.' A thought bubble: 'These are completely different things. Why are they the same type?' Clean desk, warm lighting.

A developer staring at their MCP server code. On screen: a tool called 'get_customer_profile' that fetches data but doesn't change anything. Next to it, a tool called 'send_invoice' that sends a real invoice. Both are registered as 'tools.' A thought bubble: 'These are completely different things. Why are they the same type?' Clean desk, warm lighting.

You register get_customer_profile as a tool. You register send_invoice as a tool. They look the same to Claude.

One is read-only -- it fetches data for Claude to use in its response. The other sends a real invoice to a real customer. One is harmless to call ten times. The other bills someone ten times.

Claude treats them identically. It calls both the same way. But they have fundamentally different risk profiles. One provides context. The other performs an action.