Keep Files Small

It has been long debated about at what size a code file is too big. Some say that it should be based on single responsibility principle (one class per file), others say that large files can be situationally OK and it depends on if it is causing problems.

Do not make files that are too large, if your RAG system for feeding code context can only operate on a per-file level, you will blow out your context; also, IDEs like Cursor will start failing to apply the patch created by the LLM (and even when it succeeds, it can take quite a long time to apply the patch anyway–for example, on Cursor 0.45.17, applying 55 edits on a 64KB file takes). At 128KB, you will have trouble getting Sonnet 3.7 to actually modify the entire file (Sonnet’s context window is only 200k tokens).

There is also little excuse for not keeping your files small; the LLM can handle all the drudgery of getting the imports right on your split out file.

Examples

• I asked Sonnet 3.7 in Cursor to move a small test class from a 471KB Python file to another file. Although the individual edits were small, Sonnet 3.7 did not propose well formed edits that Cursor’s patcher was able to apply.