hreflang annotations can be hard to implement properly. This tool allows you to quickly check if hreflang tags for a page (HTML and HTTP headers), and/or in an XML Sitemap, are correct.
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hreflang tags help indicate Google and Yandex in what language the content of a page is written and what audience (region) this content is targeting. This allows those search engines to serve the right content to the right user.
Certain search engines, such as Bing, do not support the rel="alternate" hreflang="x" annotations. There are three methods that can be used to help these search engines determine which language is being targeted.