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Performance obsession
The best agencies treat Core Web Vitals (LCP < 2.5s, INP < 200ms, CLS < 0.1) as contractual requirements, not aspirational targets. Run their portfolio through PageSpeed Insights.
2026
Updated
A great web design agency builds sites that convert visitors into customers. A mediocre one builds pretty sites nobody visits. Here's how to tell the difference.
The best agencies treat Core Web Vitals (LCP < 2.5s, INP < 200ms, CLS < 0.1) as contractual requirements, not aspirational targets. Run their portfolio through PageSpeed Insights.
Pretty design is table stakes. The best agencies use heatmaps, scroll maps, A/B testing, and conversion rate data to engineer sites that actually generate leads and sales.
Beware agencies that only build on one platform. The best recommend Webflow, Next.js, Shopify, or WordPress based on your needs — not what they prefer to build in.
Schema markup, responsive images (AVIF/WebP), clean URL structure, and AI Overview optimisation should be standard — not a £2,000 add-on.
Domain, hosting, CMS login, code repository, analytics accounts. Any agency that builds on their infrastructure is creating lock-in.
The first 30 days after launch always require tweaks. The best agencies include a post-launch support window at no extra cost.
London has over 2,000 web design agencies ranging from solo freelancers to 200-person studios. Average project costs run £8,000-£25,000 for a 10-15 page site. The market is fragmented — quality varies enormously. The best indicator of quality is the agency's own site performance.
See how you compare to the top web design businesses in London. 12-page PDF in 90 seconds.
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