Turn a Repeated Codex Task Into a Tested Skill

If you paste the same cleanup instructions every week, the reusable asset is the procedure and its examples, not the conversation history.

Start with one narrow task such as checking the required columns in a synthetic expense file. Write a skill that names the input, the checks and the output location. Keep a valid fixture and a malformed fixture with it, and test both after changing the instructions.

Leave unrelated jobs outside the skill. A column checker should not quietly become a payment approver because an expense looks reasonable. Codex can load a skill when its description matches the task, so make that description specific. Reuse becomes useful when the next run follows the same inspectable contract with less explanation.

OpenAI documentation.