That wasn't my point. My point was: a lot of a website's costs are hidden from a web scraper (e.g. database load), so a scraper can't claim, based on the variables they can observe (bandwidth), that they're costing the website less than normal traffic.
I was basically responding to statements like this:
> In fact, scrapers usually cause less impact because they usually don't download images or execute JavaScript.
There's really no way for a scraper to know that unless the website tells them. Their usage pattern is different than typical users and raw bandwidth (for stuff like static images) may not matter to the website.
Your argument is basically boiling down to "scrapers could hit one load-heavy endpoint too fast", but so could desktop browsers. So I don't see what it has to do with scraping.
It does, because scrapers don't have normal usage patterns. They're robots and behave like robots.
> What's the difference between a user clicking the same button on the page 50 times or holding down F5 and a scraper that pings a page once a minute?
Typical users aren't usually in the habit of mashing F5, especially not for robotically long periods of time. It's basically the difference between a theoretical activity and an actual activity.
Basically, scraping is not regular usage, and I don't think it's correct to pretend that they're equivalent (or more extremely, that scraping is less costly to the website).
For example, Googlebot does everything in its power to ensure that it sees pages the same way that end users sees them, executing JavaScript and performing OCR to try to read information conveyed in images. Google also has non-Googlebot scans to try to determine if a page is serving different content to Googlebot-labeled scans, and they penalize sites that they suspect of doing this.
While it is true that someone could write a scraper that obviously behaved robotically, it is also true that someone could use their desktop browser in a robotic way. Mashing F5 is so common that there are many ancient memes referring to and making jokes about that activity. There are extensions that end users use to record browser macros, behaviors they want their browser to repeat over and over again.
However, this conversation about whether scrapers behave robotically or not is moot because a web site shouldn't break down under load when someone uses it in a slightly-irregular way. The obvious, crappy scrapers are trivial to block. The ones that blend into the traffic are no harm, no foul. If you can't tell the difference between an optimized browser like a scraper and a general-purpose browser like Chrome, why shouldn't it be allowed to talk to your site?
Just like every university site ever is completely down during signup days because everyone is mashing F5.
Link me your site, I’ll treat it like a college student waiting to be able to sign up for their classes.
Scrapers are usually used to get publicly-available data more efficiently. What you're describing would basically require the scraper to hammer an invisible endpoint somewhere, but there's no reason the scraper would do that -- it just wants to get the data displayed by the site in a more efficient manner. I suppose the browser could enforce a cooldown on an expensive callback via JavaScript, which a scraper would circumvent, but IMO that's not a fair reason to say scrapers are disallowed; cooldowns should be enforced server-side. There's no way to ensure that a user is going to execute your script. That's just part of the deal.
Everything about scrapers means less server load; no images, no wandering around the site trying to find the right place, no heavy JavaScript callbacks that invoke server-side application load, etc. Scrapers are just highly-optimized browsing devices targeting specific pieces of data; it's logical that they would be cheaper to serve than a desktop user who's concerned about aesthetics and the like.
In our specific case, those JavaScripts we didn't download included instructions to make over 100 AJAX requests on every page load. No wonder users were looking for something more efficient.
So I agree that a scraper isn't necessarily bypassing some load-heavy operations, but I find it highly implausible that a non-malicious scraper would be invoking operations that cause extra load (beyond just hitting the site too often). Frankly, I'd be surprised if there was a functional scraper that regularly invoked more resource cost per-session than a typical desktop browsing session to get equivalent data.