SAN FRANCISCO  Alex Payne, a 24-year-old Internet engineer here, has devised a way to answer a commonly asked question of the digital age: Is my favorite Web site working today?

In March, Mr. Payne created downforeveryoneorjustme.com, as in, “Down for everyone, or just me?” It lets visitors type in a Web address and see whether a site is generally inaccessible or whether the problem is with their own connection.

“I had seen that question posed so often,” said Mr. Payne, who perhaps not coincidentally works at Twitter, a Web messaging and social networking site that is itself known for frequent downtime. “Technology companies have branded the Internet as a place that is always on and where information is always available. People are disappointed and looking for answers when it turns out not to be true.”

There is plenty of disappointment to go around these days. Such technology stalwarts as Yahoo, Amazon.com and Research in Motion, the company behind the BlackBerry, have all suffered embarrassing technical problems in the last few months.