Why I built codesize: enforcing function length limits with an AST

Every team I have worked on had some version of the rule: "keep functions short." It shows up in style guides, code review comments, and onboarding docs. It almost never shows up in CI. When it does get automated, the tooling usually reaches for wc -l on the whole file. That is a rough proxy at best. A 300-line file might contain five short, readable functions and a big block of comments. A 150-line file might contain one function that does the work of three. File length and function length are different problems. In the advent of AI, these constraints can be even more difficult to enforce. I built codesize to check the thing that actually matters: how long each function is. Why existing tools fall short cloc and similar tools count lines of code, but at the file level. Linters can flag long functions, but they are language-specific — you need a different one for every language in a polyglot repo, each with its own config format and output schema. What I wanted was a single binary that