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What Is a Toggle? What is a Slot?

Toggle is a term used to describe a switch with two positions, either on or off. You may also hear it used in reference to software or hardware features like the Caps Lock and Num Lock keys on a keyboard or the option menus on most applications. In general, toggles allow you to enable or disable functions that are normally hidden.

Toggles are a key component to any feature flag system but they must be treated with care because they can introduce subtle regressions if not designed correctly. Toggle labels should clearly state what the control will do when flipped and be easy to read. The toggle should also move into position rather than simply changing color or other visual cues to convey that a change has occurred. Additionally consider leveraging a high-contrast color to make it easier for users to distinguish between the On and Off states. Finally, don’t forget about societal and cultural differences in how colors are perceived.

Static configuration can be fine if you are using toggles for simple things but it becomes cumbersome when you start to scale. Modifying toggle configuration via static files can get messy, requiring you to manually track changes and re-deploy in order to re-configure the toggle. This is especially true for toggles used to perform multivariate or A/B testing where you need to consistently send different cohorts down different code paths.

Savvy teams view the inventory of toggles in their codebase as a resource that comes with a carrying cost and actively seek to minimize the number of toggles. This is achieved by adding a task to the team’s backlog to remove a toggle once it has been released and putting “expiration dates” on feature flags so they don’t hang around too long in your production environments.