I'm the creator of https://T.LY URL Shortener and am always interested when I see new short link services. My biggest piece of advice is to figure out a way to detect malicious URLs before your service is completely shut down. A month after starting T.LY, my servers were disabled by my hosting company without warning. Since then, I've worked on systems and tools to prevent malicious short links and make the service more reliable.

Most comments I see here are questioning why we still need URL shorteners. Print, media, SMS, and analytics are just a few reasons. I wrote some additional info on my blog: https://timleland.com/are-url-shorteners-useful-today/

Another interesting thought is when you create a TinyURL, it's 20 characters long, and Bitly links are 14 characters long. These services cannot create short links anymore. As a URL shortener grows, the number of actual short links diminishes. Currently, T.LY has over 10 million short links, which means plenty of four and five-character short URLs are available.

Two character URLs 3,844 (62^2) unique combinations

Three character URLs 238,328 (62^3) unique combinations

Four character URLs 14,776,336 (62^4) unique combinations

Five character URLs 916,132,832 (62^5) unique combinations

Six character URLs 56,800,235,584 (62^6) unique combinations

Seven character URLs 3,521,614,606,208 (62^7) unique combinations

Eight character URLs 218,340,105,584,896 (62^8) unique combinations