Your agent writes Python. The Ruby rule cuts that by a third.

Lucian Ghinda published a post arguing you should tell your coding agent to write its throwaway scripts in Ruby. Here is the block he tells you to paste into your agent's instruction file, in full: ## Scripts Write throwaway and utility scripts (data munging, one-off migrations, file renames, glue code) in Ruby, even in projects written in another language. If it needs a pipe, a loop, a conditional, or more than one line, it is a script: write it in Ruby, not Python, Node, or bash. Single self-contained commands ( `grep` , `git status` ) are fine as-is. Use only the Ruby standard library. If a gem would clearly save significant effort, stop and ask before using it. Put temporary scripts in a scratch or temp directory, not the repo root, and delete them when done unless asked to keep them. I pasted it into my global CLAUDE.md the same evening. His argument is about review: he reads Ruby daily, so when the agent writes Ruby he stays a reviewer instead of nodding at a diff. He gives three reasons and not one of them is cost. So I went looking for the number he left out. "Does the rule save tokens" only means something against what the agent writes otherwise, so the first thing I had to do was take the block back out of my global config. An agent that already carries the rule cannot tell you what it would do without it. Measuring an agent without your config in the room Every arm below runs through claude --safe-mode on Claude Opus 5, which loads no CLAUDE.md , no skills, no plugins and no hooks. Two arms deliberately skip that flag, and I name them where they appear: they are the ones that measure what my own setup does to the result. It is worth knowing that my global config alone still carries a line telling the agent to write the minimum code that does the job, and another preferring bun over node. Four tasks, one for each kind of script the rule names: munge a log, rename a key across a tree of config files, renumber a pile of screenshots, turn one CSV into another