Website monitoring is the process of testing and verifying that end-users can interact with a website or web application as expected. Website monitoring are often used by businesses to ensure website uptime, performance, and functionality is as expected.

Website monitoring companies provide organizations the ability to consistently monitor a website or server function and observe how it responds. The monitoring is often conducted from several locations around the world to a specific website, or server, to detect issues related to general Internet latency, and network hop issues, and to prevent false positives caused by local or inter-connect problems. Monitoring companies generally report on these tests in a variety of reports, charts, and graphs. When an error is detected monitoring services send out alerts via email, SMS, phone, SNMP trap, a pager that may include diagnostic information, such as a network traceroute, code capture of a web page's HTML file, a screenshot of a webpage, and even a video of a website failing. These diagnostics allow network administrators and webmasters to correct issues faster.

Monitoring gathers extensive data on website performance, such as load times, server response times, and page element performance that is often analyzed and used to further optimize website performance.

Monitoring is essential to ensure that a website is available to users, downtime is minimized, and performance can be optimized. Users that rely on a website or an application for work or pleasure will get frustrated or even stop using the application if it is not reliably available. Monitoring can cover many things that an application needs to function, like network connectivity, Domain Name System records, database connectivity, bandwidth, and computer resources like free RAM, CPU load, disk space, events, etc. Commonly measured metrics are response time and availability (or uptime), but consistency and reliability metrics are gaining popularity. Measuring a website's availability and reliability under various amounts of traffic is often referred to as load testing.

Website monitoring also helps benchmark the website against the performance of a competitor to help determine how well a site is performing. Website speed is also used as a metric for search engine rankings.

Website monitoring can be used to hold web hosting providers accountable for their service-level agreements. Most web hosts offer a 99.9% uptime guarantee and when uptime is less than that, individuals can be refunded for the excessive downtime. Not all hosts will refund individuals for excessive downtime so one must become familiar with the terms of service of their host.

Most paid website monitoring services will also offer security features such as virus and malware scanning which is of growing importance as websites become more complicated and integral to the business.

Website monitoring can be done from both inside and outside of a corporate firewall. Traditional network management solutions focus on inside the firewall monitoring, whereas external performance monitoring will test and monitor performance issues across the Internet backbone and in some cases all the way to the end-user. Third-party website performance monitoring solutions can monitor internal (behind the firewall), external (customer-facing), or cloud-based Web applications.