One thousand, not five thousand
Search for the YouTube description limit and almost every result says 5,000. That number is correct for the box under a video and wrong for the box on your channel, which stops at 1,000. People write a long About section somewhere else, paste it in, and lose the end of it with no warning.
One thousand characters is more generous than it sounds. It is around 150 words, which is enough for what the channel is, who it is for, when you upload and where to start. Most channels that fill all of it are padding.
The first sentence is the whole job
Your channel appears in search results with a snippet of roughly 100 to 150 characters taken from this box. That snippet is read by someone deciding whether to click at all. Everything you write past it is read only by people who already decided.
So the structure that works is unglamorous. Sentence one: what the channel is and who it is for, under 150 characters, no preamble. Everything else after. Starting with "Welcome to my channel!" spends a third of the snippet on a greeting.
Where the fold falls in a video description
About 150 characters show above the "more" button, and the exact point moves with screen width. Anything you genuinely need seen, a correction, a sponsor disclosure, a link to the thing you just demonstrated, has to be above it.
Below the fold is the right home for chapters, credits, gear lists and your standard block of links. Chapter timestamps need a 0:00 entry to become clickable chapters, and they want to be in order.
Write it for a person, not a keyword tool
Description text is indexed and it is shown in results, so using the words people actually search is simply sensible. Naming the software, the trade or the subject beats a clever phrase that nobody types.
The failure mode is the paragraph of comma separated phrases at the bottom. It reads as spam to a visitor and YouTube treats keyword stuffing as a policy problem rather than a ranking trick. One honest sentence containing the term does more than thirty repetitions of it.
Emoji as signposts, not as decoration
A long video description is a wall of text that people scan rather than read. A single emoji at the start of each section, one for chapters, one for links, one for gear, genuinely helps the eye find the part it wants.
What does not help is a row of them at the very top of a channel About box, because those characters come out of the 150 that search shows. Browse by meaning on our emoji keyword pages if you want one that matches the section rather than one that is merely bright.
What belongs in the About box
Four things earn their place. What the channel is, in one searchable sentence. Who it is for, if that is not obvious. When you upload, because it sets an expectation you can then meet. And where a new viewer should start, which is the single most underused line in the field.
A business email belongs there too if you want one. What does not earn its place: your life story, a list of every topic you might cover one day, and "donโt forget to smash that subscribe button", which has never persuaded anybody.