The Web.config file supplies the Website settings required for the ASP.Net web sites. These settings are like connection strings, how many users allowed, etc. Sometimes the situation arises where we need to add or remove the configuration settings without re-starting the server. This is to avoid website’s down-time. In this article, we will see a demo of how to change web config file when the site is running. Imagine that web admin of the site will access the page which we will create in this example. The goal is to add an extra web setting dynamically, and in the meantime, the server must function as usual with no re-start.