Offline and Online Modes

By default, the Force.com IDE creates projects in offline mode. When you work in offline mode, you avoid compiling your org’s Apex code each time you save your files. If, however, you have a stable Internet connection and a small- to medium-sized code base, consider toggling your projects to online mode.

Right-click your project in the Package Explorer and choose Force.com, and then select the mode in which you want to work.

When working online, the files you save are saved on the server and then retrieved from the server into your project. When working offline, files are saved locally. You can, however, save files to the server when you right-click the file in the Package Explorer and choose Force.com | Save to Server. This action is the same as when you save files while working online.