Gavior Journal · Website Development · 4 min read

Website Performance Acceptance Criteria to Put in an Agency Contract

Q: Which performance measures should a buyer use?

Core Web Vitals are useful shared measures: Largest Contentful Paint LCP reflects loading, Interaction to Next Paint INP reflects responsiveness, and Cumulative Layout Shift CLS reflects visual stability. Google publishes the metric definitions and thresholdshttps://web.dev/articles/vitals. Use those definitions rather than inventing an agency-only score, then agree on how you will interpret lab tests and real-user data.

Gavior Editorial Team

Product and web delivery editorial team

Published: 2026-10-07Updated: 2026-10-07

Specify measurable website speed and performance requirements with agreed pages, devices, test conditions and remediation ownership.

Website speed belongs in the development brief when it affects sales, search discovery or everyday usability. A vague promise of a “fast website” gives neither the buyer nor the agency a fair acceptance test. Specify representative pages, realistic devices, agreed metrics, test conditions and who fixes problems found before launch.

Contract item	Specify together	Why it prevents disputes
Page sample	Homepage, one service page, article and key transaction	One easy page cannot represent the whole site.
Device and connection	Agreed mobile and desktop profiles	Results vary widely by device and network.
Test method	Tool, settings and number of runs	One outlier run should not decide acceptance.
Third parties	Analytics, chat, video and consent tools included	External scripts can dominate load time.
Ownership	Who optimizes images, content and scripts	A slow supplied asset still needs an owner.
Remediation	Severity, deadline and retest process	Findings need a route to resolution.

Website Performance Acceptance Criteria to Put in an Agency Contract

Which performance measures should a buyer use?

Ready to turn a better idea into a better business?

Set targets with context

Test the page a visitor actually uses

Include performance in change control

Buyer checklist before signing

Gavior Editorial Team

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Accessible Business Website: A Buyer's Requirements and Acceptance Checklist

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