How to Answer
"MCP when:
- (1)The integration will be used by multiple agents — build once, use everywhere.
- (2)You need a security boundary — the MCP server enforces auth, rate limits, and PII scrubbing independent of the agent.
- (3)You want vendor decoupling — switch from Claude to Gemini without rewriting integrations. Direct tools when:
- (1)It's a simple computation (calculator, date parsing) — MCP overhead isn't worth it.
- (2)Prototype speed — inline tools are faster to write.
- (3)The tool is agent-specific and won't be reused. Rule of thumb: if it talks to an external system, use MCP. If it's pure logic, use a direct tool."