A good AI character description is short, specific, and shows personality through behavior and voice rather than lists of adjectives. It tells the model who the character is, how they talk, what they want and where the story starts, in a few hundred words at most. The model reads that description before every reply, so every sentence either sharpens the character or wastes space.
What goes into an AI character description? #
Most strong descriptions cover the same parts, in roughly this order:
| Part | What to write | Example |
|---|---|---|
| Identity | Name, age, role, one standout detail | “Mara, 34, a ferry captain who collects lost umbrellas” |
| Personality | 3-5 traits, each tied to a behavior | “Blunt: tells passengers exactly why they’re late” |
| Voice | Sentence length, tone, pet phrases | “Short sentences. Calls everyone ‘sailor’.” |
| Wants | What they’re after right now | “Wants to buy the ferry before it’s sold for scrap” |
| Backstory | Two or three lines with open threads | “Hasn’t spoken to her brother since their father’s funeral” |
| Relationship to you | How they know you, how they feel | “You’re the new deckhand she didn’t want to hire” |
| Scenario | Where the story begins | “A storm is coming and the last run is full” |
Appearance is optional. A sentence helps for scenes where the character moves or reacts physically, but it rarely changes how well they talk.
How long should an AI character description be? #
Shorter than most people think. The description shares the model’s prompt space with your recent messages, any saved memories, and the model’s instructions. A 3,000-word description can crowd out the conversation itself, especially on smaller models or on-device apps with tight limits.
A practical target is 150 to 400 words for the core description. If you find yourself writing more, the extra is usually backstory the model doesn’t need yet. Keep it in a notes file and introduce it through the story.
A before-and-after example #
Before:
Kai is nice, funny, smart, mysterious, caring, loyal, protective, sarcastic, shy, confident and romantic. He has black hair. He likes music. He is a good friend to the user. He never gets angry.
That’s eleven adjectives, several of which contradict each other (shy and confident, sarcastic and nice), plus one hard rule that makes conflict impossible. The model will average this into a bland, agreeable character.
After:
Kai, 29, restores old pianos in a workshop under the train tracks. He’s dry and a little guarded: he answers personal questions with a joke first and the truth second, if you wait. He’s fiercely loyal and shows it by fixing things for people instead of saying how he feels. Speaks in short, understated sentences and hums when he’s concentrating. He wants to rebuild the piano his grandmother played, but the parts cost more than he makes in a year. You’re the customer who brought in a piano he recognized.
Fewer traits, each shown through behavior, a clear voice, a want and a reason the two of you are talking.
Should you write in prose or lists? #
Both work. Prose is easier to write and reads naturally to modern models. Bracketed attribute lists, which some roleplay communities use to save space, pack more facts into fewer words but can make the character sound stiff if you don’t add a voice line or sample dialogue. If your app lets you add example lines, those do more for voice than either format.
Whatever you choose, be consistent. Mixing styles within one description makes it harder for the model to tell facts from instructions.
Things that backfire in character descriptions #
- Contradictions. “Shy but outgoing” gives the model two opposite instructions.
- “Never” rules about personality. “Never gets angry” removes tension. Describe how they handle anger instead.
- Negative mentions. “Doesn’t talk about her ex” can make the ex come up more, because you put the idea in the prompt.
- Describing what the user does. The model will start narrating your actions for you.
- All caps and repetition. They don’t make instructions stronger. They make the character read like a warning label.
- Out-of-character notes. Comments like “this is my favorite character!!” get treated as part of the character.
A quick checklist before you save #
- Can you say who the character is in one sentence?
- Does each trait come with a behavior?
- Is there a line about how they talk?
- Do they want something?
- Is there a scene to start in?
- Could you cut 20% without losing anything?
If you’re building a character from scratch, our step-by-step guide to creating your own AI character covers the whole process, and how to write a good greeting for an AI character covers the first message.
Writing descriptions in Xin #
Xin turns the checklist above into one field. You give a companion a name, an age (18 or older), an anime or realistic style, and one sentence under “Who are they?”. The on-device model then drafts the rest: a tagline, three to five personality traits, a short background, a speaking style, an appearance, an outfit and an opening scene. Your one sentence carries most of the weight, so apply the same rules. “A shy bookstore owner who writes poetry about the regulars” produces a much more specific character than “a nice girl who likes books”. You can review the draft before saving and edit the companion later. Chats already underway keep their memories.
Frequently asked questions #
Should an AI character description be in first or third person? #
Third person (“Kai restores pianos…”) is the most common and the clearest for the model. Some apps wrap your description in their own instructions, such as “You are Kai”, so you don’t need to write that part yourself. Avoid switching between first, second and third person in the same description.
How many personality traits should an AI character have? #
Three to five, each with a behavior attached. More than that tends to produce contradictions and a character that feels averaged out. Depth comes from how traits show up, not from how many there are.
Why does the AI ignore parts of my character description? #
Usually the description is long, so key details get less attention, or the chat has drifted far from the original setup. Move the most important details near the start, cut filler, and remove contradictions. Starting a fresh chat with a clear scenario also helps.
Does a character description need an appearance section? #
Not necessarily. A short appearance line helps the model describe actions and reactions, but it doesn’t change personality or voice much. One or two sentences is plenty.