Short answer: Don’t use them, except in special circumstances.

HTML title attributes are often perceived as an accessibility (and SEO) bonus, but the opposite is true. For screen reader users the content included inside of the title attribute is typically unnecessary, redundant, and possibly not even used. Conversely, content being put in the title attribute is being hidden from the (probable) majority of your users. If information is being hidden from the majority of your users, then it’s probably not necessary.

There are a few times when using a title attribute is appropriate:

Rule of Thumb: Serve all users equal content.

Further reading

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