The system prompts that coding agent harnesses pass to language models are massive. They describe every available tool in detail — even the ones you never use.So I wondered, what if I built something more minimal?I tend to work on small projects where all the code fits in the context window. So I built a harness with a single tool: the ability for an LLM to edit my files.The core algorithm:1. Read every file in the project directory2. Concatenate them with the user's prompt into a single message3. Send it to any language model, instructed to respond with a message and a list of edits — each edit being a search and replace on a specific file4. Apply the editsI tried getting the LLM to generate unified diffs, but it kept producing malformed ones. Search and replace turned out to be far more reliable — the model copies text verbatim from the files already in its context.This can be extended with a few more features:1. A CLI that lets you continue the conversation or reset it. Dumber LLMs ...