Use this tool to check if one or more URLs are valid Accelerated Mobile Pages (AMP) or not. If a page is not a valid AMP, click on to expand and get the detailed errors. This testing tool is using the official AMP Project validator included in the AMP JS library.
In addition to be valid according to the AMP Project specifications, "Google requires an AMP page to define the schema.org NewsArticle structured data element in order to show the page with AMP-specific display features." (Source: Google Search Console AMP report). The tool below detects the presence of such markup on the page but not its validity. To verify your structured data element, please use Google structured data testing tool.
You can also check the implementation of your AMP URLs: does the referenced canonical URL point back to the AMP with a rel="amphtml" tag?
Looking for a validator with online HTML editor? Here you go: AMP HTML Code Testing Tool