XML Sitemaps help search engines index your entire site, without having to rely on manual crawling. Usually, these can be programmatically generated, and we have working examples from Umbraco and Nuxt. Sometimes, you may have to generate it manually, or by using a tool like this one. This is especially useful for site rebuilds since you can get Google's index updated much faster by submitting your site to Google search console. Old URLs will be replaced by new ones in Google's search index.
From Google: "A robots.txt file tells search engine crawlers which pages or files the crawler can or can't request from your site. This is used mainly to avoid overloading your site with requests; it is not a mechanism for keeping a web page out of Google. To keep a web page out of Google, you should use noindex directives, or password-protect your page."
From Moz: "The meta description is an HTML attribute that provides a brief summary of a web page. Search engines such as Google often display the meta description in search results, which can influence click-through rates."
From Moz: "A title tag is an HTML element that specifies the title of a web page. Title tags are displayed on search engine results pages (SERPs) as the clickable headline for a given result, and are important for usability, SEO, and social sharing. The title tag of a web page is meant to be an accurate and concise description of a page's content."
From Moz: "A redirect is a way to send both users and search engines to a different URL from the one they originally requested. The three most commonly used redirects are 301, 302, and Meta Refresh."
If you have a testing GTM container and a production container, double-check that when you launch your site, it will use the production GTM key. Additionally, make sure the production GTM container has been published.
If your site uses a query parameter for search terms, you can easily connect this to Google Analytics.
Ideally, you will submit your XML sitemap to Google Search Console and Bing Webmaster Tools. This will alert you to issues with the crawlability of your site early, and provide valuable metrics to the analytics team. Google Search Console can also be linked to Google Analytics.
Note: Both services require some kind of verification to prove you are the owner.
The domain should work both with "www" and without "www", and one should forward to the other to avoid duplicate content issues with SEO.
So that you can assure there are no issues in production with its SSL, your staging site should also be secured. Check the console and the network developer tools in your browser to assure there are no SSL related errors.
You should have a Content Security Policy on your site. This is especially important on sites that allow user input.
From Moz: "The HTTP Content-Security-Policy response header allows web site administrators to control resources the user agent is allowed to load for a given page. With a few exceptions, policies mostly involve specifying server origins and script endpoints. This helps guard against cross-site scripting attacks (XSS)."
Make sure all of your empty states have appropriate messaging. If not, include a copywriter and designer to work on those states.
Items found by these tools may not all be fixable, but make sure you run this test and identify places you can improve your site's performance.
When in development, we sometimes install more fonts than we need. Make sure you are only requesting or only have installed font files that are actually used.
Make sure all of your images were optimized at some step in the workflow. Try to add further compression if reasonable. The technique you use may depend on your frameworks, CNDs, etc.
Use some kind of scanner to make sure you don't have any 404 errors on pages or assets.
Run your major template pages through W3Cs HTML Validator to make sure there are no errors that would hurt accessibility or other parsing issues. A CLI tool may also be an option.
Make sure your site works in the previous version of iOS's Safari browser and on the previous major version of Android in Chrome.
Review your site for any "custom widgets". Anything that updates, closes, expands, etc. that is not using native HTML functionality and add appropriate ARIA attributes.
Make sure content images have appropriate ALT attributes set, and decorative images have empty ALT attributes.
All form fields must have associated labels.
Make sure your forms have either native or custom validation and you're using the appropriate input types. Make sure invalid fields have clear error states.
The HTML tag should have an appropriate language set, according to the specifications.
Test your site for keyboard accessibility. You may find the Microsoft Accessibility Insights Tool useful for walking you through these specifications.
Check your site according to the specifications.
If deemed necessary, provide skip-to-content or skip navigation links.
Make sure your focus indicators are not turned off and visible, whether they are browser defaults or if they're styled via CSS.
It's usually a good idea if you're pulling in important JS libraries via a CDN, that you provide a local fallback.
Remove console.log and console.dir from your javascript. You might reveal data you don't want to, but it will also help if you need to ask a user to let you know what they see in their console (or take a screenshot). Leave your console.error statements though.
Make sure you've eliminated any errors, and for that matter, warnings, from the console log as possible.
If you've used a 3rd party plugin or library that requres a commercial license, make sure you're paid up and have the documentation saved in an appropriate place.
Determine if you'll have any CORS issues with any client side XHR requests.
Verify server-generated emails, like form notifications, are working.
Ideally, successful form submissions and errors can be tracked with analytics, alerting the analytics team to possible problems.
See above in accessibility, native validation is fine.
You have implemented ReCaptcha or something like it, and it will work in the production domain
Make sure you have at least a favicon for your site, but ideally, you would provide a full set of device icons.
If you think it will, or you want to encourage, social media sharing, make sure to include tags according to the Open Graph Protocol.
Check the spelling. Either in your code editor or in the browser.
Check the site and make sure there is no placeholder text, like lorem ipsum, or placeholder images.
If certain pages of your site are likely to be printed, or you encourage printing, make sure they print well by including a print stylesheet.
Verify analytics are working AND going to the correct Google Analytics account.
Use Browserstack or another computer to test this. If the webfonts are failing, but you have the fonts installed on your computer, you won't notice the failure.