Skills
Also called agent skills, Claude Skills, Gemini Skills
Saved instructions, sometimes with files, that teach an AI how to do one recurring task; it uses them when the task comes up.
Custom instructions apply to everything. A skill applies to one kind of job. It's a written recipe (steps, rules, a template, maybe an example or two) that the AI reads when you ask for that job, or when it recognises the job on its own.
The useful part is that skills are small and combine. You might have one for your company's tone of voice, one for expense reports and one for meeting notes, and the assistant pulls in the right ones as the conversation moves. That's why the big apps are moving to them from all-in-one custom bots.
Good skills are short and specific. Write them the way you'd brief a new colleague: what good looks like, what to avoid, and why.
For example
A "monthly report" skill holds your template and rules, so "do this month's report" comes out in your format every time.
Put it to use
Where you'll meet skills in ChatGPT, Gemini and Claude, how to use it there, and the mix-up most people make.
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