Ask HN: Why does Google use server side rendering for search results?

People who run online ads use A/B testing. You might ask them, "why do you use that yucky shade of green?" and they will laugh and tell you they tried a few different colors and that one got the most clicks and conversions.

If Google's ranking formula was deterministic, you could do the same thing for your search rankings. You could make changes to your page, see if your rankings get better or worse, and repeat.

If you try to do this you will find all sort of phenomena designed to gaslight you. For instance, one form of personalization is that if you click on a link that is lower down, it might move up. Well if you are always clicking on your own site it will rise higher in your rankings and you might think you've won, but really you've lost.

Other countermeasures are more conjectural, but looking from the outside I believe I've observed that Google uses randomness both on a day-to-day and a long-term basis, has different rules for sites in different parts of their lifecycles. It may be a superstition, but I have many sites that I haven't updated in years because it seems that changing a high-producing site is likely to make your site a low-producing site.

The last thing they want to do is provide an API that would make it easier to research what they do on a large scale.

People who work for Google will deny all that, but some of them are the gaslighters, while the rest are gaslit.

There is a huge industry devoted to knowing the patterns and logic behind google search to sell expertise around changing the results behind google search. A business would want this to ensure that they could be the first result when a potential customer searches for something that would indicate that they are ready to make a specific purchase that the business can handle. Politicians and other public figures would want to know how to make sure that given pages or topics do not show up like how some people theorize Boris Johnson does: https://kottke.org/19/10/boris-johnson-shady-seo-master

The issue with the industry around Search Engine optimization is that if commercial and marketing interests are too good at determining what get shown to a user, then Google loses it's value to a user. API's by design are machine readable, so if Google built its site in a way where other people can query this api directly, then marketing and PR firms would be able to query this api to build datasets on the relationships between different site, their content, and their pagerank to create rough models on how to 'game the system'. Instead by only offering a server-side rendered page for search, to collect the same information for data-mining purposes, you would need to 'scrape' the page and hope that format of the page's html is consistent for a long enough period to build a scraper, and then collect the data that they need. This combined with html and css obfuscation which is common with ssr apps and webpack in general, as well as rate-limiting and some other techniques, it can quickly become infeasible for somebody to data-mine google search for these kind of uses, and Google gets to keep their value.

With Ajax, definitely not, though I imagine some wizard will mention some mode where it can be done. Fundamentally, imagine if you started running code on partially downloaded JSON. Imagine an array of objects is partially downloaded, then the JSON is parsed, the code starts running, then suddenly more objects are added to the array later? That would be a runtime nightmare.