Marcus Halloway

Marcus has spent the last 9 years on Core Web Vitals, mostly on the browser side. He worked at Cloudflare on the Workers team, shipping early-hints and 103 response support for the Pages product, and before that did two years at Vercel debugging Next.js hydration regressions across enterprise customers. He still maintains a small open-source library for measuring CLS on client-side route transitions, which he refuses to rewrite in TypeScript on principle. His current obsession is third-party script governance: the embedded chat widgets, A/B testing tags, and CDP snippets that quietly destroy TBT on real devices. He consults part-time for two DTC brands and writes here about lab-vs-field discrepancies, the actual cost of a 200KB JS bundle on a Moto G Power, and why your synthetic Lighthouse score is lying to you.