Audisto Crawler Hints
HTML Validation & Markup Checker Technical SEO Tool
What is the HTML markup checker for
Validate HTML Implementation: Find critical markup errors like malformed URLs, invalid attributes, and improper tag usage that affect browser rendering and SEO.
Ensure Head Section Integrity: Detect issues with meta tags, canonical links, and other head elements that impact how search engines interpret your content.
Maintain Semantic Structure: Identify problems with heading hierarchy, document language settings, and HTML element relationships that affect accessibility and SEO.
Monitor Markup Quality: Track HTML validation issues across your website to maintain clean, standards-compliant code and prevent technical debt.
How to check HTML markup issues at scale
Clean markup matters
Invalid HTML markup can severely impact how search engines and browsers interpret your content. Our analysis helps you maintain clean, standards-compliant code across your website. While our quick check gives you immediate insights for single pages, our full crawler ensures consistent HTML quality across your entire website.
Critical HTML Markup related hints
<*> has malformed or empty src attribute
This hint identifies all occurrences of html elements that contain an invalid target URL in the src attribute.Learn more
<a> has malformed href
If a malformed href is found, the URL is flagged with this hint.Learn more
<a> links to fragment by name attribute on non-anchor
The anchor contains a fragment link, but the target is defined by a name attribute and is not an anchor itself.Learn more
<a> links to fragment that was not found
The anchor contains a fragment link, like "#top", but there was no corresponding id or name attribute found in the document.Learn more<base>: Contains malformed or empty href
A <base> tag was found, but its href attribute contains an invalid URL, or a URL that is neither HTTP nor HTTPS.Learn more<base>: Found more than once and differs
More than one <base> directive are found with a differing href attribute value.Learn more<base>: Href contains a path only
The <base> tag's href attribute contains a path, not an absolute URL.Learn more<base>: Occurs more than once
More than one <base> tag was found.Learn more<form> has malformed or empty action
This hint identifies all occurrences of <form> elements that contain an empty or invalid target URL.Learn more<html> contains too many uncommon non-printable characters
The HTML documents contains too many uncommon non-printable characters, and not all of them will be shown in live analysis.Learn more<html> contains uncommon non-printable characters
If uncommon non-printable characters are detected, the URL of the document containing the character is flagged.Learn more<html> starts with BOM
There is a unicode byte order mark (BOM) at the top of the HTML.Learn more<img> has no alt attribute
If an image without an alt attribute is found, the URL is flagged with this hint.Learn more<link rel=canonical>: Contains malformed or empty href
This hint identifies all occurrences of canonical elements that contain an invalid target URL.Learn more<link rel=canonical>: Found outside <head>
A canonical element was placed outside the <head> section and so search engines will ignore it.Learn more<link rel=canonical>: Found twice
More than one canonical element was found, either as a <link> tag with rel="canonical" or an according link header.Learn more<link rel=canonical>: Found twice and differs
More than one canonical element has been found, either as a <link> tag with rel="canonical" or an according Link header. Additionally, they specify different targets.Learn more<link> found outside <head>
A not allowed <link> tag was placed outside the <head> section where it may have no effect.Learn more<link> has empty, unknown or forbidden rel
This hint identifies all occurrences of <link> elements that contain rel attributes which are unknown, empty or forbidden.Learn more<link> has malformed or empty href
This hint identifies all occurrences of <link> elements that contain an empty or invalid target URL.Learn more<link> has rel and itemprop attribute
This hint identifies all occurrences of <link> elements that contain both a rel and an itemprop attribute.Learn more<meta description> occurs more than once
If a meta description is found more than once in the HTML, the URL is flagged with this hint.Learn more<meta> found outside <head>
A <meta> tag was placed outside the <head> section, where it may have no effect.Learn more<object> has malformed or empty data attribute
This hint identifies all occurrences of <object> elements that contain an empty or invalid target URL.Learn more<title> found outside <head>
A <title> tag was placed outside the <head> section, where it may have no effect.Learn more<title> missing or empty
If the <title> tag is missing, the URL is flagged with this hint.Learn more<title> occurs more than once
If the <title> tag is found more than once, the URL is flagged with this hint.Learn moreCharset: Invalid charset in Document
This hint identifies all HTML documents where the charset declaration in the HTML document specifies an invalid charset.Learn moreDuplicate id attributes
The same ID was assigned to several elements.Learn moreHreflang: Found outside <head>
An hreflang link was placed outside the <head> section and so search engines will ignore it.Learn moreHreflang: Language tags in HTML and hreflang self link differ
<link> tag with hreflang attribute points to current URL, but the language is different than the one set in the HTML.Learn moreHreflang: Self link missing
<link> tags with hreflang-attribute were found, but none of them points to the current URL.Learn moreHreflang: URL empty or malformed
<link> tag with hreflang attribute was found, but the URL it points to is invalid.Learn moreLanguage: Content-Language http-equiv meta element found
A Content-Language declaration was found as http-equiv meta elementLearn moreLanguage: Invalid
Language found does follow some basic rules for language tags.Learn moreLanguage: Set multiple times and differs
The document language was set multiple times and differs.Learn moreRobots: Specified more than once
Robots directives are specified more than once. If a document contains more than one robots definition, it will be flagged.Learn moreRobots: nofollow differs across specifications
There is more than one source for robots, either a robots meta tag or a X-Robots-Tag header, and at least one specifies "nofollow" while another does not.Learn moreRobots: noindex differs across specifications
There is more than one source for robots directives, either a robots meta tag or a X-Robots-Tag header, and at least one specifies "noindex" while another does not.Learn moreSafe HTTPS webpage loads unsafe resource
If an HTTPS webpage contains an unsafe resource that is loaded using HTTP, it is flagged with this hint.Learn moreURL too long for some browsers
If a URL longer than 2,000 characters is encountered, it is flagged with this hint, since some browsers are unable to handle URLs of this size.Learn more
Problem indicating HTML Markup related hints
<a> has no content
If a link without content is found, the URL is flagged with this hint.Learn more<a> href attribute has leading or trailing whitespace characters
If a leading or trailing whitespace gets dicovered in an HTML anchor tag, the linking URL gets flagged with this hint.Learn more<a> links to fragment by name attribute, not id
The anchor contains a fragment link, like "#top", but the target is defined by a name attribute.Learn more<h1> and <h2> not found
If no h1 and h2 headings are found, the URL is flagged with this hint.Learn more<h1> not found
If the HTML does not have an h1 heading, the URL is flagged with this hint.Learn more<h1> occurs more than once
If more than one <h1> tag is found, the URL is flagged with this hint.Learn more<html> contains more than 1500 nodes
The HTML of a page has an excessive DOM size of more than 1.500 nodes.Learn more<html> contains unencoded Left-To-Right-Mark or Right-To-Left-Mark
A Left-To-Right or Right-To-Left-Mark was found, but it is not encoded as HTML entity.Learn more<html> contains unencoded joiner chars
A zero-width joiner or zero-width non-joiner was found, but it is not encoded as HTML entity.Learn more<link rel=canonical>: URL is not absolute
If the canonical element specifies a URL relative to the document's URL, the document's URL is flagged with this hint.Learn more<meta description> missing or empty
If the meta description is missing or empty, the URL is flagged with this hint.Learn more<meta description> too long for Google snippet
If the meta description is too long to be displayed in search result snippets, the URL is flagged with this hint.Learn more<meta refresh> found
If a meta refresh is found, the URL is flagged with this hint.Learn more<title> too long for Google snippet
If the title of a document is too long to be displayed in search result snippets, the URL is flagged with this hint.Learn moreHreflang: Self link found, but document has no language
<link> tag with hreflang attribute points to current URL, but the document itself has no language set.Learn moreLanguage: Not set on document
No proper language definition was found for the HTML document.Learn moreRobots: Directive probably misspelled
A directive which is likely a misspelling of the robots meta tag was found.Learn more
Informational HTML Markup related hints
<a> has both href and onclick attributes
If a link with an href attribute and an onclick attribute is found, the URL is flagged with this hint.Learn more<a> link uses an unknown protocol
An anchor's href uses a protocol that is unknown to our crawler.Learn more<base>: Is same as URL
A <base> tag was found, but it points to the same URL, thereby rendering itself useless.Learn more<base>: Points to other URL
A <base> tag was found and it points to another URL.Learn more<h1>-<h6> chain broken
If the HTML contains a broken <h1>-<h6> chain, the URL is flagged with this hint.Learn more<html> contains unencoded soft hyphen (SHY)
A soft hyphen was found, but it is not encoded as HTML entity.Learn more<img> alt attribute exists but empty
If an image with an empty alt attribute is found, the URL is flagged with this hint.Learn more<meta keywords> found
If the HTML contains meta keywords, the URL is flagged with this hint.Learn more<meta language> found
<meta name=language> was found. Use the lang-attribute in the <html> tag instead.Learn moreHreflang: Found
<link> tag with hreflang attribute was foundLearn moreHreflang: URL is not absolute
If the hreflang element specifies a URL relative to the current URL, it is flagged with this hint.Learn moreLinks: Non-standard rel attribute value found
The rel attribute has a value without predefined meaningLearn more