Last month I led a workshop on writing tooltips, and I was tempted to make a one-slide presentation that said "How to use tooltips: Don't."
Tooltips can be helpful, but more often than not they're used inappropriately. The mindset of Well I don't know where to put this, so I'll throw it in a tooltip is an all too common one, but I get it. Minimalism is a design heuristic that argues that everything on a screen should be there for a reason; users are trying to accomplish a goal, and the most straight-forward route is the one to take. Just think about trying to merge into the correct lane on a highway when a dozen signs are overhead—it's overwhelming.
Tooltips are the worst of both worlds: they're invasive, often block important content, and usually contain information that no one really needs to know; they're also hidden, inaccessible, and sometimes hide info that's needed to move forward.
What an enigma, the old tooltip.
And therein lies the problem: UX writers need to make sure that everything on the page has earned its place, but a tooltip's very nature dictates that it's extra. If the two big problems are unnecessary info and vital info, what's the happy medium?
The answer's in the name. Tip. Tooltips are designed as a nice to have item, like a side dish or a condiment to a meal: not necessary but can add a little something extra, and the experience is still okay even if it's overlooked.
Wix has a great article on writing tooltips, and one of my favorite examples is their regional tooltip. If a user doesn't hover over it, fine; they get the main idea from the field alone. But the tooltip explains how the setting works in more detail, and what exactly will be affected. For users with a business or international audiences, this could be good to know.
Consider an example from NNG, which focuses on a password creation flow. It's common enough to see password requirements hidden within a tooltip, but look how placing the info in a subtitle makes it so much easier to read and discover.
Kill the tooltip with fire. Honestly, it's how I feel most days, because most tooltips that currently exist...shouldn't. If you're considering adding a tooltip to your design, ask yourself if the copy lies within that sweet spot of being complementary but not repetitive, overkill, or central. If it passes that test, fine: it's earned its place in your design.
But deciding if it should exist is only half the battle. When it comes to writing tooltips:
Keep it short. No, seriously. I always say that good UX writing is often short, but it doesn't have to be; it should just aim to be clear and concise. With tooltips, short is the word of the day. No more than a sentence or two.
Stay accessible. Tooltips just aren't accessible. Most are only activated on hover or on a timer. That said, you can lessen the damage by leaving out rich content (bold, italics, etc.) and links.
Test it out. If you're able to test the flow, check out how many people actually read the tooltip and, out of those who do, whether they understood it and found it helpful. If not, go back to the notebook for a rewrite.
Put all your tooltips through that test, and you'll come to love the ones that stick around.