How URL shorteners work

URL shortening, sometimes called link shortening, is used to shorten long and nasty URLs into something more readable and shareable.

At its very essence, a URL shortener is a link that 301 redirects into a new destination.

When you create a short-link with any link shortening service (be it Linkly, Bitly, or any of a number of others), a new link is inserted into a database, which returns a numeric ID.

This number might be very long, and numbers certainly aren’t very attractive on the end of URLs: e.g.

shor.tr/2385162034

Link shorteners get around this by changing the base of the number.

In base 10, numbers go from 0 to 9 before you add another digit (10) and start all over again.

In base 16 (hexadecimal), numbers go from 0-15, however the numbers 10-15 are represented by the letters A through F.

So, for example, the number 11 would be B.

The long number in the link above would be 8E2AAF32 - a bit shorter, but not much shorter.

Link shorteners tend to use Base 62, which gives you:

• The numbers 0-9 (10 symbols)
• The lowercase letters a - z (26 symbols)
• The uppercase letters A - Z (26 symbols)

For a total of 10 + 26 + 26 = 62 symbols.

Now, let’s encode the number above using Base 62:

2385162034 in Base 10 = 2bPtb0 in Base 62

This is now six characters (as opposed to 10), yet still uniquely identifies the link.

All link shorteners work on similar principles.

When a request comes for a link, the extension is converted back to Base 10, the database queried for that link ID, and the user is redirected to the destination for that link.

A link shortener might at this point record the request, in order to provide click tracking functionality.