steve sparks
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ContentsPart III · Chapter 11

Chapter 11How it all fits together

The whole loop

The model thinks, the prompt tells it the situation, the harness runs the show, and the tools let it act. Take one away and you get either a clever text predictor that can't do anything, or a toolbox with no one deciding what to use.

Diagram of an AI system. You talk to the harness, never directly to the model. The harness builds a briefing (the prompt and context) and sends it to the model. The model replies with an answer or a tool request. For a tool request the harness checks permission, runs the tool (web search, files, code, company systems) and adds the result to the briefing, looping until the answer goes back to you. How an AI system fits together You Harness the body and workshop: the app around the model Builds the briefing instructions, your message, notes, earlier results Prompt the briefing folder Checks the rules allowed? risky? asks you first if needed Runs the tool and collects the result Model the brain: predicts the next words Tools the hands: web search, files, code, email, company systems 1 2 tool request 3 4 result added 5 the answer, handed back by the harness 6 Model thinks. Prompt informs. Harness manages. Tools act.

Step through it, or pick a part below to see what it does.

  1. You ask a question.
  2. The harness builds the briefing: its instructions, your message, notes it keeps and earlier results.
  3. The model reads the briefing and predicts a reply: either an answer, or a request for a tool.
  4. For a tool request, the harness checks the rules, asks you if needed, and runs the tool.
  5. The result goes back into the briefing, and the model reads it again. This loop repeats until the job is done.
  6. The harness hands the final answer back to you.

Use it in a slide: SVG · PNG (free to use in your own slides and talks, with credit to Steve Sparks and a link to aifromthepartsup.com)

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Using this book

© 2026 Steve Sparks. All rights reserved. You're welcome to quote short passages and cite any page, with a link back. To reuse diagrams or larger parts, ask through GitHub.

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