URL Parameter

Every web page has an address that you see at the top of the browser. Often, at the end of this address there is a question mark, followed by more characters. Everything that comes after this question mark is a URL parameter. These are additional pieces of information that get sent along to the computer on the other end. An example: on a video platform, the addition “?v=abc123” means that exactly the video with the identifier abc123 should be played. The address itself indicates which page is opened, while the parameters indicate what exactly this page should show.

Why addresses need to do more than just name a page

Without parameters, you would need a separate address for every conceivable variant of a page. An online shop with shoes in twenty sizes, ten colors, and three price tiers would end up with hundreds of fixed pages. With parameters, a single page suffices, which assembles itself differently depending on what’s attached. This saves effort and makes the offering flexible.

A second advantage is that the state of a page can be shared. Someone who has filtered a search for red sneakers in size 43 can copy the address and send it along. The recipient will see exactly the same filtered view. Without parameters, the selection would only be stored in one’s own browser and could not be passed on.

However, the flip side is also important. Parameters are visible to everyone and can be changed by hand. An address with “?user=admin” must therefore never be the sole determinant of who has access to something. Anyone who manages security via URL parameters is building a lock whose key is taped to the outside of the door.

Question mark, equals sign, ampersand

The structure always follows the same pattern. The question mark separates the actual address from the parameters. This is followed by a name, an equals sign, and a value, such as “language=en”. If several pieces of information need to be sent along, they are joined with an ampersand: “?language=en&sort=price”. You can think of it like a form whose filled-in fields are strung together in a single line.

Not all characters are allowed in an address. Spaces, umlauts, or the ampersand itself would break the structure. That’s why such characters are re-encoded — a space, for example, becomes “%20” or a plus sign. This process is called URL encoding and happens automatically in the background.

The server, i.e. the computer that delivers the page, reads out the parameters and reacts to them. It searches its database for matching entries and assembles the page accordingly. Sometimes, however, only the browser itself evaluates the information, without anything new being loaded. Which names a service understands is determined by the operator. Unknown parameters are simply ignored.

From search results to advertising tracking

Parameters are most commonly encountered with search engines. The term you typed in lands directly in the address, usually as “q=” or “search=”. Page numbers in long lists, language switchers, and filters in shops also work this way. Once you start paying attention, you’ll spot them on almost every larger website.

Parameters also play a distinct role in marketing. Appended codes such as “utm_source” tell the operator which channel a visitor came from, for example an email or an ad. This information doesn’t change the page being displayed; it merely serves analytical purposes. That’s why they often show up when you open links from newsletters or social networks.

In the tech world, parameters are also mentioned in connection with interfaces through which programs exchange data. An AI service, for instance, can be told the desired model or output format this way. A common misconception is that parameters are the same as cookies. Cookies remain stored in the browser, whereas parameters only apply to a single request and disappear afterward.