Character Prompt: Definition and Where Each App Uses It

Quick answer

A character prompt is the standing instruction that defines a character: personality, backstory, speaking style and scenario.
It is the community name for what developers call a system prompt, written as a character definition.
Documented sizes differ: Character.AI allows up to 32,000 characters; SpicyChat advises about 900 to 1,100 tokens; Janitor AI advises under 2,500 permanent tokens.
For how to write one, see our creator guide on writing a character prompt.

What Is a Character Prompt?

A character prompt is the standing set of instructions that sets a chatbot's role, tone and rules for a character, sent to the model ahead of the conversation. The general idea is the system prompt. Anthropic's documentation says: "Setting a role in the system prompt focuses Claude's behavior and tone for your use case. Even a single sentence makes a difference." In companion and roleplay apps the same idea is written as a character definition.

"Character prompt" is community terminology, not a term defined by a standards body. In the character card format the material is split into fields such as description, personality, scenario and system_prompt. The V2 spec says frontends should by default replace the user's global system prompt with the card's system_prompt value.

Character Prompts in Named Apps

App	Where it goes	Documented size guidance
Character.AI	Character Definition: personality, backstory, speech patterns, rules, example dialogue with {{char}} and {{user}} placeholders	0 to 32,000 characters
SpicyChat	Personality, plus optional Scenario and Example Dialogue	Personality up to 5,000 characters; whole definition about 900 to 1,100 tokens advised
Janitor AI	Personality (required, include example dialogue), scenario, initial message	Under about 2,500 permanent tokens, best under 1,500
CrushOn.AI	Description, which acts as permanent memory	Around 1,500 tokens recommended
Kindroid	Personality and Backstory, Response Directive, Key Memories, Example Messages	Personality 2,000 characters (2,500 for subscribers)
Nomi	Backstory+ sections such as Backstory, Inclination and Current Roleplay	Field limits not found

These are the official fields and sizes from each app's help pages, checked October 2026. Replika uses a free-text backstory, and its help text advises third-person, positive wording. The fields behind each platform are compared in apps with custom characters, and the app pages (Character.AI, SpicyChat, Janitor AI) list the rest.

Why Length Matters

Because the character prompt is sent ahead of the conversation, it shares the context window with the chat. Janitor AI's guidance counts the definition as "permanent tokens" against a context of about 8 to 9K tokens. As general advice, put the traits that decide behavior first and keep the rest short. For tone and consistency, see AI character personality design, and for the AI behind it, how AI girlfriend apps work. More terms are in the glossary.

FAQ

Is a character prompt the same as a system prompt?

Close. A system prompt is the general term for standing instructions to a model. A character prompt is that idea written as a character definition. In the card format it can also be a separate system_prompt field.

How long should a character prompt be?

It depends on the app. SpicyChat advises about 900 to 1,100 tokens, CrushOn.AI around 1,500 and Janitor AI under 2,500, while Character.AI allows far more characters. Check the platform's own guidance first.

Can I reuse a character prompt in another app?

Often by copying the text into the matching fields. SpicyChat and CrushOn.AI also import character files; see the card format entry.

Sources

Official pages and store listings we read for this page (last check October 20, 2026).