MCP Academy · Lesson

Idempotent, Side-Effect-Aware Tools

Make repeated calls safe and predictable.

Models May Call Twice

An AI client can retry a tool after a timeout or a dropped link. Your tool might run twice for what the user meant once.

What Idempotent Means

A tool is idempotent when calling it again with the same input changes nothing further. The second call is safely a no-op.

All lessons in this course

  1. Layered Server Architecture
  2. Config & Secrets via Environment
  3. Idempotent, Side-Effect-Aware Tools
  4. Versioning Tools & Schemas
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