How you shape an AI assistant's personality and guardrails is more important than which model you pick.
The single biggest factor in how useful Woodhouse is day-to-day is not the AI model — it is the instructions that define how he thinks and behaves. Get this right and even a smaller model performs surprisingly well. Get it wrong and a frontier model will still frustrate you.
Woodhouse has a SOUL.md file — literally a document describing his personality, values, and style. Sharp. Direct. Dry. No filler. Trusted colleague energy, not eager assistant. This sounds abstract but it has a real effect on every response he gives. When I changed “be helpful” to “be genuinely helpful, not performatively helpful”, the quality of responses noticeably improved.
Beyond personality, AGENTS.md covers operating rules: when to ask before acting, how to handle memory, what counts as a hard line. The hard rules section is particularly important — things like “never commit to GitHub without explicit permission in the current conversation” exist because I learned the hard way what happens without them.
The takeaway: spend time on your instruction files. They are the most leveraged investment you can make. A well-crafted SOUL.md outperforms model upgrades for day-to-day quality.