[SEO Audits] Write documentation

Some SEO audits point to existing support documentation and other external sources. We want to have documentation of all of Lighthouse’s audits in one canonical place (d.g.co/tools/lighthouse or jsdoc). Additionally, we should use these LH-specific docs to describe the exact pass/fail conditions for each audit and guidance on how to fix common failure reasons.

@kaycebasques, feel free to work with @kdzwinel on any implementation details of the audits and reach out to Lizzi for peer reviews.

Documentation checklist:

• Document has a <title>
• Images have alt text
• Has a <meta viewport>
• Page has successful HTTP status code
• Document has a <meta description>
• Document has a valid hreflang code
• Document has a rel=canonical
• Anchors have descriptive text
• Avoids plugins
• Document uses legible font sizes
• Page is not blocked from indexing
• robots.txt is valid
• Tap targets are sized appropriately
• JSON-LD structured data is valid

This list will be updated as we add more SEO audits.

[mfriesenhahn]

@mfriesenhahn should #9537 close this? Does web.dev have full coverage of all the bullet points above?

Yep, web.dev has a doc for each bullet. #9537 takes care of most of them, with the following exceptions:

• #9084 includes “Document has a <title>” and “Images have alt text.”
• #9539 includes “Has a <meta viewport>.”

I’m still tidying up the web.dev docs to address feedback from the Lighthouse team, but I expect to have the SEO ones done in the next day or two.

[kaycebasques]

Yes, I can work on the robots.txt doc