One sentence beats a character sheet
A character needs a role, a want, a way of speaking and a limit. Those 4 fit in a sentence and they determine almost everything the character does. Longer descriptions dilute them, because every extra adjective competes for the same attention.
The instinct is to write a page: appearance, history, favourite colour. Almost none of it shows up in the dialogue, and the parts that would have shown up are buried among the parts that do not.
The role sets the vocabulary
A dock worker and a diplomat use different words for the same idea, and the role is what supplies that. Naming an occupation or a position does more for the voice than any list of traits, because vocabulary is the first thing a reader notices and the first thing a model gets right.
The want drives every scene
A character with no want reacts; a character with a want acts. This is the element most often missing, and its absence is why a well-described character still feels passive. One clause is enough: wants to be believed, wants the money, wants out.
The way of speaking is not the accent
Sentence length, directness, whether they answer the question asked. These carry more than a written accent, which tends to arrive as spelling tricks and gets tiring in 3 lines. Short and blunt is an instruction; gruff is an adjective.
The limit is what makes them a person
Something the character will not do, and it should cost them. A limit creates the only interesting moments in a scene, because it is the thing the story can push against. Without it a character agrees to everything, which is the most common failure of all.
Before you start
What about appearance?
Include it only where it changes behaviour. A limp changes how a character crosses a room; an eye colour changes nothing that appears in dialogue.
Can I add more later?
Yes, and adding as it becomes relevant works better than front-loading. Detail introduced in a scene sticks; detail listed in advance is often ignored.
Does a longer sheet ever help?
For a long story with continuity to maintain, a short reference list of facts helps. That is a memory aid rather than a character description.
Write one sentence with a role, a want, a voice and a limit.
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