There are many "alternate search" websites that allow you to search content from a website—Twitter, Facebook, Instagram, Discord channels—outside of the website.
Strictly interpreted, are such sites in violation of any laws or open to liability?
One the one hand, they are using content that isn't theirs; on the other, Google does this.
Many of these sites use what's called an application programming interface (API) that will take data that the user inputs into the application's User Interface (UI aka the part of the website you see) and gives the website the command. This is sent through a script language to the backend, which processes the input data and returns output data. If part of that command goes to a third party site, it triggers a second call to the third party site's API, which takes that input into it's back end and returns it to the back end of the app. When everything is processed, the Back End returns the output to the UI.
In other words, many of these services use API developed by the website to access it's content.
A second method is called "Screen Scraping" where a computer automates traveling through a website's UI and putting in the input data, looking at the results, and returning the data to the end user. How this works is by the program parsing through the html source code of a website, which is visible to any user with the access (you can see the source code of any page you want on your own by doing a right click on page in your browser and looking for an option to "View Page Source" or similar wording. It will typically pop a simple text editor (normally Notepad) and will show the HTML code the page is written in. There are several programing tools that can parse this and look for data by knowing how it's listed in page code and... So say I wanted to know Law Stack's average score of it's front-page feed... I would code a screen scraper to go to the page, wait for the data to load, look at all the scores based on how the scores are written to display in the source code and then math that all up and spit out the average.).
