Once your website has been developed and content added to it. Next step is to check your website for different errors & accessibility issues.
Below are some helpful sites & tools for this purpose.
The W3C Markup Validation Service:-
Website Markup Validation Services
Website Speed Test:-
Website Loading Speed Checking Tool
If you have used CSS (Cascading Style Sheets) on your website, this CSS Validator Tool will help you finding errors (if any) in your CSS code.
Link Checker Tool:-
Check your site links/anchors for errors with Link Checking Tool
Feed Validation Service:-
Check the syntax of atoms or rss with Feed Validation Service
Check your website’s color contrast and color brightness to make sure the contrast is high enough for people with visual impairments. Color Contrast Checking Tool
Website Accessibility Checker:-
With Website Accessibility Checking Tool, you can check the accessibility of Web pages according to the Guidelines by Web Content Accessibility specifications.
Cross Browser Testing:-
Check your website how it looks on different browsers with Cross Browser Check
Mobile Friendly Test:
Check how your website looks like on mobile….Google Mobile Friendly Test
Note: Don’t worry if your website is unable to pass on all of these sites, but try to make sure your site clears most of the compatibility tests on the checking tools mentioned here as it will improve your website usability, user experience & increase traffic in result.