You’d like the DeArrow browser extension.

DeArrow is an open source browser extension for crowdsourcing better titles and thumbnails on YouTube. The goal is to make titles accurate and reduce sensationalism. No more arrows, ridiculous faces, and no more clickbait.

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Titles can be any arbitrary text. Thumbnails are screenshots from specific timestamps in the video. These are user submitted and voted on. By default, if there are no submissions, it will format the original title to the user-specified format, and set a screenshot from a random timestamp as the thumbnail. This can be configured in the options to disable formatting, or show the original thumbnail by default.