Developer Builds Couples Therapy App with Claude, Shares Prompt Engineering Insights

A developer has built TherapAI (therapai.health), a progressive web app for couples where each partner gets a private AI companion that helps process emotions and share when ready. The app runs on Claude Sonnet.

Key Prompt Engineering Learnings

The developer shared specific techniques learned while making Claude feel like an actual therapist rather than a chatbot:

• Tell it what NOT to say: Banning phrases like "I hear you," "that's valid," and "thank you for sharing" was the single biggest quality improvement. These phrases create an "instant uncanny valley" effect.
• Trust tiers: Session 1 Thera doesn't pretend to know the user, while Session 30 Thera can push back and call out patterns. This creates conversations that feel like an actual developing relationship.
• Trait blending: Users pick 2-3 personality traits (Honest, Calm, Deep, etc.), with each trait implemented as a separate instruction block. Claude blends them naturally without flip-flopping between personalities.
• Inject mood, don't ask about it: Users pick their mood before the session, and the AI adapts its tone silently without explicitly stating "I see you're frustrated."
• Shorter = deeper: Explicitly instructing Claude: "If they share something vulnerable, respond shorter, not longer. Weight, not volume."

Technical Implementation

The app has a minimal stack: the entire application is a single HTML file, using Supabase for data and a Netlify function as an API proxy to Claude. The app is live at therapai.health with a 7-day free trial.