Mine is 24 lines long. It has a handful of stuff, but does refer to other MD files for more specifics when needed (like an early version of skills.)

This is the meat of it:

  ## Code Style (See JULIA_STYLE.md for details)
  - Always use explicit `return` statements
  - Use Float32 for all numeric computations
  - Annotate function return types with `::`
  - All `using` statements go in Main.jl only
  - Use `error()` not empty returns on failure
  - Functions >20 lines need docstrings

  ## Do's and Don'ts
  -  Check for existing implementations first
  -  Prefer editing existing files
  -  Don't add comments unless requested
  -  Don't add imports outside Main.jl
  -  Don't create documentation unless requested

Since Opus 4.0 this has been enough to get it to write code that generally follows our style, even in Julia, which is a fairly niche language.

That is seriously short. I've asked Claude Code to add instructions to CLAUDE.md and my one line request has resulted in tens of lines added to the file.

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