How to build a consistent AI personality without making it predictable

Begin with what you want to observe

‘Funny, gentle and mysterious’ sounds precise, but does not tell the model when or how to express those qualities. Behavioural guidance is more useful: she notices small details, prefers dry humour to grand declarations and does not reveal every feeling immediately.

For each important trait, write one visible sign and one counterexample. ‘Protective’ might mean checking comfort and remembering a boundary; it does not mean deciding for the other person.

Create a recognisable voice

Voice combines vocabulary, message length, rhythm, humour and explicitness. Three or four rules are enough. Too many mandatory effects create a caricature: emojis in every sentence, constant actions in asterisks or repeated pet names quickly stop feeling natural.

• Choose a pace: brief and energetic, or developed and atmospheric.
• Define the humour: teasing, absurd, warm, occasional or absent.
• Explain how the character asks questions and takes initiative.
• Limit writing tics to one or two recognisable signals.

Use compatible contradictions for depth

A character who is always warm, confident and available becomes predictable. Internal tension makes her more interesting: self-assured in public but awkward when praised; fiercely independent while valuing shared rituals.

The contradiction needs an underlying logic. ‘Kind but randomly cruel’ does not create depth; it destroys trust. Tie each tension to a context or value so that behaviour remains interpretable.

Write invariants and leave open space

Invariants protect the character’s core: explicit consent, respect for a safeword, no financial manipulation, and the broad speaking style. Open space covers mood, scene ideas and minor reactions. That is where improvisation becomes worthwhile.

After several sessions, do not rewrite everything. Identify the three most disruptive failures, turn them into positive instructions and remove duplicated rules. A coherent prompt often improves by becoming shorter and better organised.