Building an AI Agent Platform with Next.js 16 and Claude: A Technical Deep-Dive

Last month I shipped AgentDesk — a SaaS platform where consultants and agencies can run pre-built AI agents for client intake, proposal generation, and reporting. The stack is Next.js 16, Claude Sonnet 4 with tool use, Stripe subscriptions, and Vercel. This post walks through the architecture decisions and actual code that powers it. The Problem Every consulting firm does the same repetitive work: qualifying inbound leads, writing proposals from call notes, generating client reports. These tasks follow predictable patterns, which makes them perfect candidates for AI agents — not chatbots, but structured agents with defined tools and outputs. I wanted to build a platform where each agent has a specific job, uses typed tools, and produces structured output that plugs directly into existing workflows. Architecture Overview The project uses Next.js 16.2.1 with the App Router, React 19, TypeScript, and Tailwind CSS 4. The core is a central agent engine that defines agent configurations and