As a webmaster, you know the importance of Uptime and Downtime. Downtimes occur due to many different reasons such as server problems, Spike in web traffic, or high load on the server causing high CPU Uses, etc. So as a webmaster, you cannot monitor your website manually 24-7.
But there are many website monitoring tools available on the web that allows users to monitor their website performance, the current status of their websites, and overall uptime and downtime statistics of website and web applications.
Best Website Monitoring Tools
Pingdom

It can distinguish genuine downtime from routing and access problems and alert you when your server goes down or any error face by your server.
Down for everyone or just me?

The site has a straightforward user interface, just like Google.com. Is it open with a plain screen with the question: Is ______ down for everyone or just me? Users fill in the blank with the site they wish to check and click the link (the “or just me” portion of the question).
Site24x7

Features :
- Website uptime monitoring
- Server Monitoring
- Website Performance monitoring
- Global monitoring Network
- Monitor web application
- Receive Instant Email
- Receive Instant Email
- Alert and notifications
- Monitor DNS Servers
- Mail Server Monitoring
- SLA Management
- Website Monitoring Reports
Uptime Robot

It’s an easy and efficient way to monitor the uptime of your websites. It allows users to watch as many as fifty websites and receive instant SMS, RSS, Twitter, and email alerts when a site is showing as offline.
CodeGuard – Website Backup & monitoring tools

If C.G. finds any performance changes on your site, it will automatically take a new backup and notify you via email. It also allows you to restore your website/database to a previous version.