[solutionyogi]

Twitter gets millions of tweets and I am sure good percentage of them will have URLs. And if they start checking valid response for each URL, I think soon they will have to build a new data center just for this task. Also, what if the URL is temporarily down? What should they do?

[natrius]

I don't think they need to check for valid URLs. My point is just that disguising text as a URL will be possible regardless unless you check for 404s or ellipsize the URLs. Using a URL shortener isn't necessary to make URLs count for a constant character length.