Topic collection
Website Performance
Find the causes of slow pages and make measured improvements for real visitors.
guide · 11 min read
Why Is My Website Slow?
Diagnose slow hosting, oversized images, JavaScript, third-party scripts and Core Web Vitals with a prioritised website speed checklist.
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Build your understanding
Why Is My Website Slow?
Diagnose slow hosting, oversized images, JavaScript, third-party scripts and Core Web Vitals with a prioritised website speed checklist.
What Are Core Web Vitals?
Understand LCP, INP and CLS, the difference between field and laboratory data, and how to improve real website experience without chasing scores.
How to Test Website Speed Properly
Use website speed tests without confusing one synthetic run with real-user performance or guaranteed Core Web Vitals.
How to Check SSL and HTTPS
Understand public SSL checks, expiry warnings, redirects, mixed content and why HTTPS is not a complete security assessment.
How to Optimise Images for a Website
Choose dimensions, quality and formats that reduce transfer size without damaging important visual detail.
How to Use the Core Web Vitals Checker
Prepare reliable inputs, understand the Core Web Vitals Checker output and review its limitations before applying the result.
How to Use the Redirect Checker
Prepare reliable inputs, understand the Redirect Checker output and review its limitations before applying the result.
How to Use the Broken Link Checker
Prepare reliable inputs, understand the Broken Link Checker output and review its limitations before applying the result.
How to Use the Mobile Friendliness Checker
Prepare reliable inputs, understand the Mobile Friendliness Checker output and review its limitations before applying the result.
How to Use the Favicon Checker
Prepare reliable inputs, understand the Favicon Checker output and review its limitations before applying the result.
How to Use the DNS Lookup Tool
Prepare reliable inputs, understand the DNS Lookup Tool output and review its limitations before applying the result.
How to Use the Domain Expiry Checker
Prepare reliable inputs, understand the Domain Expiry Checker output and review its limitations before applying the result.
How to Use the HTTP Header Checker
Prepare reliable inputs, understand the HTTP Header Checker output and review its limitations before applying the result.
Free tools
Put the advice to work
Website Speed Checker
Run a limited live response and page-weight check, with PageSpeed support when configured.
SSL Checker
Check public HTTPS availability, redirects and visible mixed-content indicators.
Image Optimiser
Resize and convert an image locally using the browser canvas, with no upload.
Core Web Vitals Checker
Check public PageSpeed laboratory data when the PageSpeed integration is configured.
Redirect Checker
Follow a safe public request and compare the submitted and final addresses.
Broken Link Checker
Test a limited sample of same-site links found in a public page’s initial HTML.
Mobile Friendliness Checker
Review selected mobile-readiness indicators available in a page’s initial HTML.
Favicon Checker
Find favicon declarations and resolve their public URLs from a page’s HTML.
DNS Lookup Tool
Look up selected public A, AAAA, MX, NS and TXT records for a website domain.
Domain Expiry Checker
Request current registration events from a fixed public RDAP service when available.
HTTP Header Checker
Review selected public response, cache and content headers for a webpage.