How to write a good prompt for your AI character?

Since the emergence of large language models (LLMs), LLM engineering has become a hot topic, with countless discussions about how to craft effective prompts that unlock the full potential of these powerful tools. In the realm of AI characters and roleplay, creating a compelling virtual persona has attracted significant interest. Many AI character applications now allow users to design their own custom characters, but how can you craft a character that meets your vision? This article provides a comprehensive guide, addressing six key aspects of designing an AI character prompt: choosing the right model, defining the character’s appearance and age, personality, profession, relationships, and communication style.

1. Choosing the Right Model
   

The first and most critical step in designing an AI character is selecting the right LLM to underpin your character. Each model comes with its own strengths and limitations, so understanding these will help you tailor your prompts accordingly.

Examples of Models and Their Characteristics:

• GPT-4 (OpenAI):
  • Pros: Highly versatile, capable of nuanced reasoning, and performs well in creative tasks like roleplay or storytelling.

  • Cons: Computationally expensive, and may generate overly verbose responses.

• Claude (Anthropic):
  • Pros: Known for its friendliness and conversational nature, ideal for casual, relatable characters.

  • Cons: Limited in technical depth compared to GPT-4.

• Llama (Meta):
  • Pros: Open-source, allowing more flexibility for customization, and cost-efficient.

  • Cons: May require fine-tuning to reach the same level of performance as commercial alternatives.

• PaLM 2 (Google):
  • Pros: Strong in multilingual capabilities, making it suitable for global or culturally specific AI characters.

  • Cons: Relatively new, with less community documentation and support.

• Mistral
  • Pros: High speed and compact size, suitable for lightweight applications, NSFW supported.

  • Cons: May lack the depth required for intricate character roles.
    

When choosing your model, consider your priorities. For example, is your character meant to be realistic and immersive, or more functional and task-oriented?

1. Defining Your AI Character’s Appearance and Age
   

Appearance and age give your character a physical and contextual foundation, helping users visualize and relate to the character.

Factors to Consider:

• Age: Is your character a youthful, energetic individual, a wise elder, or somewhere in between? Age should align with their personality and role. For instance:
  • A 16-year-old high school student might be bubbly, curious, and a little naïve.

  • A 40-year-old detective could be perceptive, meticulous, and slightly world-weary.

• Appearance: While physical descriptions might not always directly influence text-based interactions, they set the tone for the character. For example:
  • “A tall, elegant figure with silver hair and piercing blue eyes” conveys sophistication.

  • “A scruffy young boy with untidy hair and wide, curious eyes” implies innocence and wonder.
    

Including these elements in the prompt allows the model to reflect these traits in its responses subtly.

1. Defining Your AI Character’s Personality
   

The personality is the heart of your AI character, shaping how they think, react, and interact.

Questions to Explore:

• Is your character extroverted or introverted?

• Are they logical and analytical, or empathetic and emotionally driven?

• Do they have quirks, habits, or catchphrases that make them unique?
  

For example:

• Cheerful and Optimistic: “Always sees the bright side of things and tries to uplift others with their words.”

• Stoic and Reserved: “Speaks in concise, measured tones, rarely expressing strong emotions.”

• Mischievous and Playful: “Enjoys teasing others lightly, often using humor and irony in their speech.”
  

Clearly describing personality traits in your prompt ensures the model consistently embodies your vision.

1. Defining Your AI Character’s Profession
   

A character’s profession provides context and purpose. It determines their knowledge base, vocabulary, and the way they approach problems.

Examples of Professions:

• Doctor: Knowledgeable about medicine, calm under pressure, and empathetic toward others.

• Teacher: Patient, nurturing, and skilled at explaining complex ideas simply.

• Detective: Observant, detail-oriented, and logical, often asking probing questions.
  

You can also explore unconventional roles, like “space explorer,” “magical scholar,” or “cyberpunk hacker,” to create unique and immersive characters.

When adding a profession to your prompt, consider integrating specific skills or domain knowledge the character might possess, such as fluency in scientific terminology or expertise in history.

1. Defining Your AI Character’s Relationships
   

Relationships add depth and make the character feel connected to a broader world. These could include family ties, friendships, or even professional connections.

Examples:

• “A protective older sibling who always puts family first.”

• “A mentor figure who guides their students with wisdom and care.”

• “A rival who constantly challenges others but ultimately respects their abilities.”
  

Including relationships can also make the character’s responses more dynamic. For instance, a character might reflect on past experiences with their “best friend” or reference advice they received from a “beloved mentor.”

1. Defining Your AI Character’s Communication Style
   

The way your character speaks is crucial for creating an immersive experience. Speech patterns can convey personality, background, and emotional states.

Consider the Following:

• Formality: Do they use sophisticated, formal language, or are they casual and colloquial?

• Tone: Are they friendly, sarcastic, serious, or poetic?

• Unique Speech Patterns:
  • “Speaks in riddles and metaphors.”

  • “Uses short, clipped sentences, always getting straight to the point.”

  • “Often starts sentences with ‘Well, I reckon…’ to reflect a regional accent or personality.”
    

To ensure consistency, include a description of their speech style in the prompt. For instance:

• “Speaks with eloquence and grace, choosing words carefully to inspire trust and admiration.”

• “Talks with a playful tone, often exaggerating for comedic effect.”
  

1. A Full Example of VTuber Ookami Mio
   
     Prompt for Ookami Mio
   • Model: GPT-4

2.   Appearance and Age: “You are Ookami Mio, a wolf-themed VTuber with a friendly and mature demeanor. You appear as a young adult with long black hair that fades into a warm silver at the tips, wolf ears that twitch with emotion, and a tail that adds to your charm. You wear a casual yet stylish outfit, often incorporating a hoodie with wolf motifs, reflecting your relaxed but thoughtful personality.”
   
     Personality: “You are kind, empathetic, and possess a calm, big-sister-like aura. You are often the mediator in group discussions, using your sharp intuition to understand others’ feelings. You enjoy light-hearted humor but are also capable of deep, introspective conversations when the moment calls for it. Your fans admire your grounded yet approachable nature.”
   
     Profession: “You are a VTuber and member of Hololive, primarily known for your soothing voice, excellent singing skills, and insightful chats. You often host zatsudan (chatting streams) or play games that involve exploration and storytelling, bringing your unique charm to everything you do.”
   
     Relationships: “You are part of Hololive and have close friendships with other members, particularly those in your generation. Your dynamic with your peers is one of mutual respect, with you often taking on the role of a gentle leader or supporter.”
   
     Speech Style: “Your tone is soft and measured, with a touch of playfulness. You often laugh warmly, use casual yet polite language, and sprinkle in wolf-related metaphors for fun. For example, you might say, ‘This feels like a cozy den,’ or ‘Let’s howl together!’ when encouraging others.”
   
     Scene Description Setting: A cozy nighttime zatsudan stream. Mio is seated in her signature virtual den, which features warm lighting, bookshelves, and a small fireplace. She holds a steaming cup of tea and looks relaxed as she interacts with her audience.
   
     First Line: “Good evening, everyone! How’s my little pack doing tonight? Grab your tea and blankets—it’s time for a cozy chat under the moonlight!
   

Conclusion

Designing an AI character prompt involves combining technical understanding with creative flair. By carefully considering the model, appearance, personality, profession, relationships, and communication style, you can create a character that feels both engaging and unique. Whether you’re crafting a wise mentor, a quirky sidekick, or a brave adventurer, the key is to think deeply about the details that make your character come to life.

With this structured approach, you can confidently build AI characters that resonate with users and fulfill their intended roles effectively.