As search engine crawlers (and in particular Google) continue to integrate rendering into their crawling and indexing process, as SEOs we need to pay increasing attention to the effects of rendering on our web pages.
If the rendered HTML contains major differences to the response HTML, this might cause SEO problems. It also might mean that you are presenting web pages to Google in a way that differs from your expectation.
If these things are changing during rendering, why are they changing?
And perhaps more pertinent still: should they be changing?
All this is to say that differences in the rendered HTML is not inherently bad, and the intention of the comparison feature is twofold;
And one other thing, that might not be obvious - if you have a site whereby no content is changed during rendering, you don't need to concern yourself with this sort of thing, and crawling with the HTML Crawler is perfectly adequate for carrying out audits.
The first thing to note is that this report is only available using the Chrome Crawler, which you need to select during the initial audit setup:
Make your other data analysis selections, and start the audit running. When using the Chrome Crawler, it will automatically create the Response vs Render report, which is accessible in the left hand menu:
You will be presented with 6 pie charts, which show the effects of rendering on each of 6 key SEO elements: Meta robots, Canonical, Title, Meta Description, Internal Links, External links.
The pie chart segments correspond to:
Clicking on the corresponding chart segment (or number in the data table below) will bring you to a URL List showing you all the affected URLs, and the relevant data:
The 6 key elements are shown as different pie charts in the report:
You want to pay particular attention to:
Bear in mind that 'index' is the default status, and 'noindex' is an explicit instruction to not index the page content.
This is particularly important when you consider that if Google find 'noindex' in the response, they will not render the page at all. Any kind of mismatch in the meta robots should be investigated as a matter of priority, as it can impact indexing and therefore rankings.
With this one, if the canonical URL is different in the rendered HTML, the important question to ask is, 'is this the correct canonical URL?'.
After meta robots, this is possibly the most important of the elements analysed in this report, as link signals feed into Google's evaluation of page strength and relevancy.
For both internal and external links (below), the pie chart segments are actually slightly different: