Toggle is a button, lever, switch, or software setting that allows users to select between two options or states. It is an important type of control used for updating user preferences, settings, and the like. Toggles are easy to use when they are designed well. They should be clear, consistent, and deliver immediate results.

A toggle should be recognizable as such by its shape, color, and other visual signifiers. They should also provide a clear explanation of their function and state, especially when they are first introduced to the user. In addition, toggles should be designed in a way that reduces cognitive overload by only showing one or two options at a time.

The most obvious visual sign of a toggle is the color that differentiates the on and off states. For best practice, designers should consider contrast and cultural differences when selecting colors to signal toggle states. A good rule of thumb is to choose a high-contrast color with a strong visual differentiation from the background.

Another important visual cue is the font size of a toggle’s text. We tested four different font sizes, ranging from minimal to substantial. The results showed that the largest font difference performed the worst, but that all other font size differences were acceptable. It is recommended to use a bold-thin combination as the primary font for toggle text in order to achieve sufficient contrast. Embossment was another visual cue that we tested and found to be unreliable at communicating the active state of a toggle. It is much better to pair embossment with a stronger visual cue, such as a solid border.

When it comes to the functionality of a toggle, it is important to test all possible configurations before deploying them into production. This will include testing the toggles that are expected to go live with their default state flipped Off as well as the fallback configuration where those features are disabled. For some applications it may also be advisable to test the toggles that are expected to go live and those that will be flipped On as well, since this can prevent surprise regressions.

The ability to dynamically re-configure specific service instances at runtime is a powerful tool in the hands of a team. However, it is easy to mis-use this capability and introduce chaos into a shared environment. If this is going to be a requirement for an application it may be more appropriate to utilize a distributed configuration system rather than forcing a developer to restart the application in order to flip a feature flag.