Link to explanations

[googlechrome]

Link to explanations

[paullewis]

Yeah since this was based on @PaulKinlan's logic, I'm wondering if he can elaborate. First I've come across it as a criterion for a Progressive Web App.

[Garbee]

@paulirish Just pushed commit 71c4680 which added an inline note about this.

imo if that note is accurate and it is "just a warning" then:

1. We should have an "intermediate" state for things like this. Yellow icon and warning triangle.
2. Anything like this should not show Red since they aren't necessary.
3. As Rob is asking for, let's link to documentation to help developers along in deciding whether or not they should apply a given practice. Whether intermediate or outright failure of error states.

[paullewis]

Yeah we need some version of severity in here.

[Garbee]

btw, I think canonical URLs are an SEO aspect.

[robdodson]

yeah I was less concerned about the severity and just a general explanation of how I fix the problem :)

[Garbee]

Webmaster docs on the topic. Should be very enlightening.

cc @PaulKinlan in case there is other relevant documentation to add here to explain why Canonical URLs are encouraged.

[addyosmani]

Fwiw, a lot of the existing PWAs we've shipped pass all of the tests minus the canonical URL one. It's unclear to me why it's a must-have vs. nice to have for SEO purposes :)

[cwilso]

It would be nice to more clearly describe the canonical URL one. For building a simple site, where you DON'T have multiple ways to get to the content, you still have to put in a rel=canonical link, with "".

[paulirish]

these are mostly in now.