What's the difference between a browser engine, a rendering engine and a user agent?

Question

What is the role of user agent switcher?

https://addons.mozilla.org/en-US/firefox/addon/59

Is the user agent different than the rendering engine?

If a browser uses the same rendering engine then do we need to check on every browser?

Answer 1

• A rendering engine is the engine that a browser uses to render the html (i.e. gecko vs webkit).
• A user agent is how a browser identifies itself (i.e firefox 3.5).

But even if you switch the user agent of lets say firefox to safari, it will still use the gecko rendering engine to render it's page.

So to check how a page renders in different browsers you really need to render the page in those different browsers.

Answer 2

Role of User Agent Switcher is mainly to switch one browser to another browser which is called User agent. This is how all the server side language identifies through which software their application is accessed and which device etc.

What Wikipedia says about User agent?

When a software agent operates in a network protocol, it often identifies itself, its application type, operating system, software vendor, or software revision.

Have a look at Browser Arch and list of engines for each browser.

Browser Architecture

Browser Engines List

What is Rendering Engine?

• Layout / Rendering Engine able to render the content of given URL in browser screen and interprets the HTML, XML and CSS.
• It is single threaded. By default.
• It displays data according to your specified content type (MIME). For Example HTML, Images, XML, CSS, JSON, PDF etc.

Click here to Refer to my Article to understand what is there behind Browser. https://medium.com/@ramsunvtech/behind-browser-basics-part-1-b733e9f3c0e6

Answer 3

Some websites render content differently according to the User Agent that is being sent. For example, if the User Agent is IE 6, the language used to render the webpage (e.g. PHP) could be used to add a class "ie6" to an element, and then CSS is used to control what gets displayed or not. Or, a separate js file can be added depending on the user agent.

Some years ago, Opera recommended that you set the User Agent as IE 6, because websites will consistently not render if the User Agent was not any of IE or Mozilla. But, I think this is no longer the case.