What is the best way to keep a URL from appearing in search results?
Use the META robots NOINDEX tag
Google's Page Speed Insights, WebPageTest.org, GTMetrix, Pingdom, DevTool's (Network panel, LightHouse, coverage report), checkgzipcompression.com, (specific reports in Google analytics)
HTTP Strict Transport Security
Activates your voice-based digital assistants (Example: Alexa , Echo, Amazon, Ok Google)
Sitemap: 50,000 URLs, 50MB uncompressed (52,428,800 bytes)
Index Sitemap: not list more than 50,000 Sitemaps
Where should the X-Robots-Tag be located
In the HTTP header
Google Webmaster Central Blog
The Keyword
Google Research Blog
Google Analytics Solutions
Language (in ISO 639-1 format)
Region (in ISO 3166-1 Alpha 2 format) [optional]