Engineers write prompts as part of the job now, and being able to refer to them in an efficient manner is a valuable improvement to your workflow. Skip pasting file contents into Claude entirely: open find-file (C-x C-f) to surface the path Emacs already knows, select it and cut it …

When Claude delegates a prompt to a sub-agent, it pastes the whole prompt text into that sub-agent's context by default — thousands of tokens, duplicated, every time. Tell it to hand over a file reference instead of the copied text, and that one change alone can cut input tokens 25-40%.

I got my ⭐️...

I am not committing to the Advent of Code 2025 this year. I'm working on too many side projects checksmix, snipren, emomtimer. In fact I don't even have time to write this blog. On the other hand, I used some holiday downtime to work through Day 1 …

Blazing Fast MMIX Emulator

I like learning computer architectures by running code. MIX is good fun, but it’s dated and awkward for writing anything beyond small examples. MMIX, on the other hand, is a complete computer architecture—much closer to machines that were genuinely pleasant to program, like MIPS …

I rename a lot of files. So do you.

I respect the Unix way — mv file1 file2 — but in practice, file1 and file2 are usually the same name failing by one to three characters. Re-typing 97% of a filename feels ceremonial rather than intentional, especially when what I want is …

C-x C-x is teleport for your mark.

C-x h is “select literally everything right now”!