A prompt library is any place where you keep your reusable prompts: a Word document, an Excel sheet or a notebook page all work. Save a prompt once it gives you good results, then swap the details the next time you use it. That saves rewriting the same instructions again and again.
- When a prompt is good and you use it a lot, turn it into an agent.
More in Prompting tips
What should I write in Custom Instructions?
Describe how you work and communicate, and let the AI draft the instructions for you, because it explains things to itself better. In Copilot, a strong approach is to ask it to analyse your sent emails and write instructions that match your style. Then paste the result into the custom or draft instructions box.
What is the difference between Custom Instructions and Memory in AI?
Custom instructions hold your stable preferences, such as language, tone and role, and are sent with every message. Memory holds things that change over time. If the two contradict each other, the newest memory usually wins, but a memory is never created without you, so you stay in control.
Is there a limit on how many Memories AI can save?
It depends on the tool. In paid Copilot you are unlikely to hit a limit on memories, while tools like Claude and Mistral do cap them. Custom instructions are limited to about 8,000 characters because they are sent in full with every message. Memories are separate items, and only the relevant ones are pulled in.