Thumbnail text can clarify a contrast, question, or result. It can also compete with the image and repeat information already supplied by the title. Decide what the words contribute before adding them.
Give the text a specific role
Use a short phrase that changes how the image is understood. A measurement, a brief question, or a meaningful label may help. A full sentence explaining the entire video often belongs in the title or description rather than inside a small graphic.
Write for quick recognition
Choose familiar wording and enough contrast to keep the letters distinct. Avoid elaborate fonts when they make the message slower to read. The phrase should remain meaningful if the viewer sees it briefly rather than studying it as a designed poster.
Check accuracy and placement
Do not cover the feature that proves your point. If the video compares two objects, place labels where their association is obvious. Keep every claim consistent with the footage. A large word such as free or instant should not hide a condition that materially changes the offer.
Compare with a text-free version
Make a copy of the design without the lettering and review both at small size. If the subject becomes clearer without text and the title already explains the missing context, the simpler version may communicate better. This is an editorial judgment, not a universal rule that thumbnails should always contain or always avoid words.