Simon Willison’s Weblog

My LLM codegen workflow atm (via) Harper Reed describes his workflow for writing code with the assistance of LLMs.

This is clearly a very well-thought out process, which has evolved a lot already and continues to change.

Harper starts greenfield projects with a brainstorming step, aiming to produce a detailed spec:

Ask me one question at a time so we can develop a thorough, step-by-step spec for this idea. Each question should build on my previous answers, and our end goal is to have a detailed specification I can hand off to a developer. Let’s do this iteratively and dig into every relevant detail. Remember, only one question at a time.

The end result is saved as spec.md in the repo. He then uses a reasoning model (o3 or similar) to produce an accompanying prompt_plan.md with LLM-generated prompts for the different steps, plus a todo.md with lower-level steps. Code editing models can check things off in this list as they continue, a neat hack for persisting state between multiple model calls.

Harper has tried this pattern with a bunch of different models and tools, but currently defaults to copy-and-paste to Claude assisted by repomix (a similar tool to my own files-to-prompt) for most of the work.

How well has this worked?

My hack to-do list is empty because I built everything. I keep thinking of new things and knocking them out while watching a movie or something. For the first time in years, I am spending time with new programming languages and tools. This is pushing me to expand my programming perspective.

There's a bunch more in there about using LLMs with existing large projects, including several extremely useful example prompts.

Harper ends with this call to actions for the wider community:

I have spent years coding by myself, years coding as a pair, and years coding in a team. It is always better with people. These workflows are not easy to use as a team. The bots collide, the merges are horrific, the context complicated.

I really want someone to solve this problem in a way that makes coding with an LLM a multiplayer game. Not a solo hacker experience. There is so much opportunity to fix this and make it amazing.