Building a Reusable Custom Assistant for a Repeated Task

Any task you repeat more than weekly is worth packaging. The gain is not just time; it is consistency of output.

Pick the right task

Good candidates are narrow and repetitive: converting a weekly report into a fixed format, drafting replies in a house style, reviewing submissions against a checklist. Broad assistants with vague purposes do not get used.

Write instructions as rules

• State the output format explicitly, with a short example.
• List what to never do — invent numbers, change quoted text, alter terminology.
• Specify behaviour when information is missing: ask, or mark as unknown.
• Keep it short. Every line is loaded on every request.

Attach reference material as files

Style guides, templates and glossaries belong in uploaded files rather than in the instruction text. Files are cheaper to maintain and easier to replace when they change.

Test with three real cases

Run one typical case, one edge case and one that should be refused. Adjust the instructions until all three behave. Then share it with the people who will use it and ask which outputs they had to fix.

Review quarterly

Instructions accumulate cruft and reference documents go stale. A short review keeps the assistant trustworthy, which is the only reason anyone will keep using it.