HTML Structure
Valid DOCTYPE declaration
Every page starts with <!DOCTYPE html>. Without it, browsers switch to quirks mode and render inconsistently.
Check with HTML ValidatorNo unclosed tags
Every opening tag has a matching closing tag. Unclosed divs and spans cascade layout bugs.
Check with HTML ValidatorProper nesting
Tags are nested correctly. No <div><p></div></p> patterns that break document structure.
No duplicate IDs
Every id attribute is unique on the page. Duplicate IDs break JavaScript selectors and accessibility.
Valid character encoding
<meta charset='UTF-8'> is the first tag in <head>. Prevents garbled characters on international content.
Language attribute set
<html lang='en'> is set. Helps screen readers pronounce content correctly and search engines serve the right version.
SEO Essentials
Unique title tag on every page
Under 60 characters, primary keyword first. The most important on-page SEO element.
Check with Meta Tag CheckerMeta description present
Under 160 characters, compelling, includes target keyword. Affects click-through rate from search results.
Check with Meta Tag CheckerCanonical URL set
<link rel='canonical'> points to the preferred URL. Prevents duplicate content issues.
Heading hierarchy is correct
One H1 per page, followed by H2s, then H3s. No skipped levels (H1 directly to H3).
All images have alt text
Descriptive alt attributes on every img tag. Required for accessibility and image SEO.
Check with Accessibility Checkerrobots.txt is valid
No accidental disallow rules blocking important pages. Sitemap URL is declared.
Check with Robots.txt CheckerXML sitemap is submitted
Sitemap.xml lists all important pages and is submitted to Google Search Console.
Social Sharing
Open Graph tags present
og:title, og:description, og:image, og:url, and og:type are set on every page.
Check with OG CheckerOG image is 1200x630px
The recommended size for all major platforms. Must be an absolute URL.
Twitter card tag set
At minimum twitter:card is set to summary_large_image for full-width previews.
Social preview tested
Check how your page looks when shared on Facebook, LinkedIn, and Twitter before launch.
Check with OG CheckerAccessibility
All images have alt attributes
Screen readers need alt text to describe images to visually impaired users.
Check with Accessibility CheckerForm inputs have labels
Every input, select, and textarea has an associated <label> element.
Color contrast is sufficient
Text has at least 4.5:1 contrast ratio against its background (WCAG AA).
Page is keyboard navigable
All interactive elements can be reached and activated with keyboard only.
Performance
No render-blocking resources
CSS and JS in <head> block rendering. Use async/defer for scripts, inline critical CSS.
Images are optimized
Use WebP/AVIF, proper dimensions, lazy loading on below-fold images.
Page weight is reasonable
Total page size under 3MB for good mobile performance. Check with our tool.
Check with Page Size CheckerCSS is valid
Invalid CSS is silently ignored by browsers, causing invisible bugs.
Check with CSS ValidatorRun All Checks Automatically
Our tools automate most of these checks. Start with the HTML validator and work through the list.
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