# Builder

For agents that write and change code from a brief: a command, a site, a page or a migration.

## What is in it

*Figure: lever: When the work isn't trivial, it has your agent write the script that does it, rerun it on the first unit and diff the result against the hand version. prove-it: Before your agent says it is done, it runs the real program from outside and reads what it prints, instead of trusting a compile, a cached screenshot or its own word. first-principles: When a rule changes, it redesigns the type model or module from the start instead of adding another special case. error-messages: Rewrites a vague error or validation message so it names exactly what went wrong, which rule failed and what to do next, without blaming the person. eval-design: It turns 'is the agent better now?' into a question asked of many items of real work, with a named judge and a figure you can track. encode-lessons: When the same correction comes up a second time, it picks the cheapest guard that holds it (a type, a lint rule, a hook or a script) instead of adding another line of text. state-machines: Design each module as a state machine.*

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Published 2026-10-29. Web page: https://www.mackenziebowes.com/kits/builder Part of [Kits](https://www.mackenziebowes.com/kits).