Understand
Playbook
Three things that belong together: the lessons, for how this actually works; the craft guides, for working with it without a surprise bill; and the glossary, which defines every term used anywhere on this site.
Never used one of these before?
Start at the beginning and read seven short pages.
About forty-five minutes end to end, in order, each one assuming the one before it and nothing else.
The lessons
In order. Each builds on the one before.
- What a language model actually isA next-token predictor, and why that description is both accurate and far too small.
- Tokens, and why everything is counted in themThe unit everything is counted and charged in, and why it is not words.
- Generative, agentic, and the gap between themThe difference between a model that writes and a model that acts, and why it matters for your bill.
- What it costs, and why the surpriseWhere the money actually goes, which is rarely where people expect.
- Vibe coding, honestlyBuilding by describing and steering, and the part of it that genuinely goes wrong.
- How a model gets madeFour stages, and the fact that almost all of the behaviour comes from the cheap ones.
- The landscape, brieflyWho makes these, how they differ, and what actually constrains your choice.
The craft guides
Practical, and each one comes with something you can move — using the real prices from the catalogue, not worked examples.
Start here
- Choosing a modelThere is no best model; there is a best model for a task at a price.
- Working inside a context windowA context window is a budget spent on every call, not a memory that accumulates.
- Keeping the bill downOutput usually costs three to five times input — long answers cost more than long questions.
Going deeper
- Running an agent without a surprise billThe context grows on every pass, so the last turn costs several times the first.
- Prompt caching, and when it costs you moneyReading from the cache is cheap; writing to it costs more than sending normally.
The glossary
33 terms, defined so each can be read without already knowing the other 32. Every one of them is linked from the word itself wherever it appears on this site — and the Explain jargon button in the header puts the definition inline, in the sentence.
33 terms.