Realtime Collab
A collaborative editor with granular permissioning and low-latency updates using WebSockets and event-sourcing.
React • WebSocket • Node.js
Discuss
Build fast, reliable web experiences.
I'm Kai Mercer — a full-stack developer focused on performance, accessible design, and scalable systems. I craft interfaces and APIs that teams love and users trust.
Selected Case Study
Designing a realtime collaboration platform — performance, security, and delightful UX.
About Me
I build modern web applications with a focus on performance, reliability, and human-centered design. With a background in both product and backend engineering, I bridge the gap between design intent and robust implementation.
Frontend
React, TypeScript, Tailwind CSS, accessibility, component libraries.
Backend
Node.js, Go, PostgreSQL, scalable APIs, authentication & observability.
Architecture
Cloud-native patterns, event-driven systems, performance optimization.
Design
Design systems, prototyping, inclusive interactions, motion design.
Selected Projects
A curated selection showcasing technical depth and product focus.
Health Analytics
End-to-end stack for capturing, processing, and visualizing telemetry from mobile devices with privacy-first architecture.
Go • PostgreSQL • Kafka
Discuss
Commerce Platform
Scalable headless commerce with modular APIs for catalogs, orders, and checkout optimizing for conversion and speed.
TypeScript • PostgreSQL • Vercel
Discuss
Observability Suite
Distributed tracing and metric pipelines with a lightweight UI to detect regressions and alert intelligently.
Elasticsearch • Prometheus • React
Discuss
Design System
Reusable components, tokens, and accessibility guidelines used across multiple products to accelerate delivery.
Storybook • Tokens • Accessibility
Discuss
Serverless Platform
Efficient serverless pipelines to manage bursts in traffic with low operational overhead and clear SLAs.
AWS • Lambda • Step Functions
Discuss
Services & Expertise
From audits to full product delivery — I partner with product teams and founders to ship impactful software.
Product Engineering
End-to-end delivery: planning, architecture, implementation, and scaling with measurable outcomes.
Performance Audits
Comprehensive audits with prioritized recommendations and fixes to improve load and interaction times.
Architectural Reviews
Scalability and reliability guidance for growing systems, including cost-performance trade-offs.
Mentorship & Training
Team training on modern workflows, testing, and pragmatic coding standards.
What clients say
Trusted by founders and engineering leaders.
Jessica ParkCEO, Finix"Kai transformed our product velocity — shipping clean, maintainable code and a design system that scaled across teams."
Marco SilvaCTO, Healthline"Reliable, pragmatic, and great at communicating trade-offs. Helped us re-architect critical systems with minimal disruption."
Anika RoyProduct Lead, Shoply"An excellent balance of design sensibility and technical rigor. The improvements directly increased conversions."
Get in touch
Interested in working together? Tell me about your project and I’ll get back within 48 hours.
Typical engagements
2–6 week audits · 3–6 month engagements · fractional CTO
Response time
Initial reply within 48 hours + detailed proposal within one week
Want a tailored audit? I offer a focused 2-week performance & accessibility audit that surfaces high-impact improvements.