Guillermo Casanova

I'm a senior software engineer with 5+ years across startups, fintech, e-commerce, and AI-native products. I build agent infrastructure, fast web and mobile interfaces, and observable, cost-aware systems.

My work centers on three areas. AI systems: agent workflows, tool calling, structured outputs, prompt caching, model routing, LLM evaluations, and production observability loops. Product engineering: TypeScript, React, Next.js, TanStack Start, React Native, Expo, Node.js, NestJS, Supabase, and Redis. Platform and quality: Vercel, GCP, Terraform, Playwright, Vitest, PostHog, Sentry, performance budgets, and release automation.

I own outcomes across product surfaces rather than only ticket boundaries, treat performance and cost as metrics to observe, and prefer direct architecture until real system pressure justifies more complexity. For operating beliefs and influences, see Essence. For writing, see Thoughts. To get in touch, see Contact.