When to use which

Every recurring instruction comes down to two questions.

1. Is it a constraint or a procedure?

• A constraint (what must or must not be true) is a rule. Always on, so keep it short.
• A procedure (how to do something) is a skill. Loaded when relevant or when you invoke it.
• Guidance that only matters sometimes is a skill too, even if it reads like a constraint. Rules load every session; skills cost almost nothing until they're needed.

2. Who needs it?

• Only this repo: commit it to the repository.
• Only you: your personal level.
• Your team across repos: your organization.
• Everyone, by policy: the enterprise.

Everything else stays in the prompt. A one-off detail about this task, like the ticket, the bug, or the file to change, belongs in the prompt and nowhere else.

Already using playbooks? Keep running them, but write new procedures as skills.

Start small and let it compound. Capture a rule when Devin gets something wrong. Write a skill when you repeat yourself or when Devin figures something out. Every addition makes the next session more autonomous and shorter, which means fewer ACUs.