CloserCoach
Voice-AI Sales Coaching Platform · $60K+ MRR
Tech stack
Architecture highlights
- VAPI real-time voice + Langfuse prompt observability
- Firebase Realtime DB for live analytics
- Retry-safe webhook workers for 50K+ daily events
The problem
Sales reps had no scalable way to practice and get objective feedback — human coaching didn't scale past a handful of calls per week.
What I built
I architected the backend and infrastructure from scratch (Node.js, Express, Firebase) for an AI sales-coaching product that runs realistic voice roleplays and returns instant, structured feedback.
Key features
- Real-time voice roleplay via VAPI with < 1.5s feedback latency
- AI analysis of 10,000+ daily sales conversations
- Admin dashboard: analytics, user management, revenue tracking
- Webhook pipeline handling 50,000+ callbacks/day with retry logic
The hardest challenge
Guaranteeing sub-1.5s feedback while processing tens of thousands of voice callbacks daily — solved with an idempotent, self-healing webhook pipeline and Langfuse-tuned prompts.
The full story
Problem
Human sales coaching doesn't scale. Reps needed unlimited, realistic practice with objective, instant feedback.
Research
I evaluated real-time voice providers and prompt-observability tooling, landing on VAPI for voice and Langfuse for prompt engineering and tracing.
Architecture
Node.js + Express APIs, Firebase Realtime Database for live analytics, and a retry-safe webhook worker layer to absorb 50,000+ VAPI callbacks per day.
Implementation
I built the entire backend and infrastructure from scratch: voice session handling, the feedback pipeline, an admin dashboard with revenue tracking, and idempotent webhook processing.
Result
The product sustains 500+ daily signups and $60K+ in monthly recurring revenue, with 99.9% webhook reliability and sub-1.5s feedback latency.
Lessons learned
At real-time voice scale, idempotency and retry logic aren't nice-to-haves — they're the product. Designing the webhook layer to self-heal was the single highest-leverage decision.
Outcome
- $60K+ monthly recurring revenue enabled
- 500+ daily signups sustained
- 99.9% webhook reliability at 50K+ events/day