Prompt character limit: how much text each model takes
The prompt character limit is set by the model, not by the site as a whole: on MarketVideo, Kling 3.0 takes up to 2,500 characters, while Seedance 2.5 Omni and the Nano Banana models accept 20,000.
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A counter under the field tracks the length as you type. So the useful question is less how to phrase things beautifully and more what has to fit. Below are the ceilings, the order in which to trim when space runs out, and a way to name your uploaded photos inside the text so the model knows which is which.
Character ceilings by model
Kling 3.0 cuts the field off at 2,500 characters. Seedance 2.5 Omni and the Nano Banana family go up to 20,000, and a few special modes stop much earlier, around 500 to 1,000. Near the edge the counter lights up; past it the run button goes grey and nothing is sent, so overshooting spends no stars. Trust the counter of the field you are in rather than a figure from memory.
What to cut first when you run out of room
Trim by priority, not evenly. Evaluative words such as beautiful, professional or atmospheric go first: they name no visible feature but eat space that background or framing could use. Light goes next, then secondary detail. Subject and action stay. The last line to survive is the request to keep a person's face unchanged; without it the likeness drifts and every other detail loses value.
Pointing the text at your uploaded photos
With several photos attached, the text can refer to each one. Where the form numbers its upload slots as image1, image2 and so on, put that tag right into the sentence, written exactly as the slot shows it: image1 walks down the street in the jacket from image2. The model then knows which picture holds the person, the object and the background. First and last frame modes need no tags.
How the templates spend their space
The cards below are full prompts written by people who hit the same ceilings. Vintage Oil Paint Portrait opens with an instruction to preserve the face and proportions from your photo, and only then describes the pose. Bold Flat Character Poster splits its text into labeled parts such as a format lock. Borrow that order for your own prompt: likeness, subject, setting, light.
Three characters or twenty thousand
The lower edge is almost a joke: three characters. The form accepts such a prompt and returns a result, and everything left unnamed is the model's choice. That is useful only as a probe, to see whether a model takes on a theme at all. At the other end, 20,000 characters is about ten pages, and text that long usually describes two scenes that belong in two separate runs.
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FAQ
Do spaces and line breaks count toward the limit?
Yes. The counter adds up every character, spaces, line breaks and punctuation included. A prompt laid out as a vertical list therefore fills the field faster than the same idea written as one running paragraph.
What happens if I paste text longer than the limit?
The field takes the whole paste, the counter goes over, and the run button stays inactive until you remove the excess. The tail is never trimmed silently, so the model never receives half a task.
Is the limit the same for photos and videos?
No, it belongs to the model, not to the type of result. Among video models you will find both 2,500 and 20,000, and the Nano Banana photo models also take 20,000. Check the counter under the field you are actually using.
How long should an AI prompt be?
Long enough to name the subject, the action, the setting and the light, plus a line about keeping a face if a person is in the shot. Most images need far less than the ceiling; a prompt that keeps growing often holds two ideas that work better as two runs.