Feature Toggle vs Feature Flag: What's the Difference?

Are Feature Toggle and Feature Flag the Same Thing?

A feature toggle and a feature flag describe identical systems: you define a named switch, evaluate it at runtime against a user context, and branch your code based on the result. The evaluation happens locally in an SDK, with no network call per request. You can change the switch in a dashboard and see the effect in your application immediately, with no deployment.

// "Feature flag" or "feature toggle" — same SDK call either way
const decision = userContext.decide('rel_checkout_v2')

if (decision?.enabled) {
  return <CheckoutV2 />
}
return <CheckoutV1 />

If someone on your team says “flip the toggle” and someone else says “flip the flag,” they mean exactly the same action. The only thing that differs is which term each person was exposed to first.

History of the Terms

“Feature toggle” — the original term (2010)

Martin Fowler popularized the term “feature toggle” in his 2010 article on the pattern. Fowler was writing for a British technical audience, and “toggle” — meaning to switch between two states — was the natural word choice. The article is thorough and remains the canonical reference for the pattern; it's worth reading regardless of which term you use.

The term “feature toggle” spread quickly through the continuous delivery and extreme programming communities, where trunk-based development and frequent releases were already established practices.

“Feature flag” — North American adoption

Simultaneously, engineering teams at companies like Facebook, Flickr, and later Google and GitHub were building similar systems and calling them “feature flags.” “Flag” — as in a binary flag in computing — resonated naturally with American engineering culture. The term spread through conference talks, blog posts, and the founding of dedicated feature flag platforms (Optimizely, LaunchDarkly) in the early 2010s.

By 2015, both terms were in widespread use. Today, “feature flag” is more common globally — it's the term used in most SDK documentation, platform names, and job descriptions — but “feature toggle” is still frequently used, particularly in the continuous delivery and DevOps communities.

What Other Names Are Used for Feature Flags and Toggles?

You'll encounter several other terms that all refer to the same pattern:

“Feature gate” deserves a note: at companies like Meta, a “gate” often implies a permission check — “is this user gated into this feature?” — whereas a “flag” or “toggle” implies a rollout or experiment. In practice, many teams use “gate” and “flag” interchangeably. The implementation is the same regardless.

Which Term Should You Use?

It doesn't matter — pick one and be consistent. Here's a practical framework for making the choice:

• Use “feature flag”if you're writing public documentation, job descriptions, or choosing a tool name. It has broader recognition today and is the term most engineers will search for.
• Use “feature toggle” if your team comes from a continuous delivery background and already uses the term — consistency within the codebase matters more than following an external convention.
• Whatever you pick, standardize it in your codebase: variable names, comment style, internal documentation. Having half the team write FEATURE_FLAGS and the other half write FEATURE_TOGGLES creates unnecessary friction.

Frequently Asked Questions

Is there any technical difference between a feature toggle and a feature flag?

No. The terms describe the same pattern: a named runtime switch, evaluated against a user context, that controls code branching without a deploy. Any technical distinction you encounter (e.g., “toggles are binary, flags can be multivariate”) is informal and not standard — the underlying concept is identical.

What is a feature gate?

A feature gate is another synonym for a feature flag, commonly used at Meta (Facebook) and Airbnb. In some contexts “gate” implies a permission check (is the user allowed to access this feature?) rather than a rollout or experiment, but the implementation is technically the same.

What's the difference between a feature flag and a kill switch?

A kill switch is a type of feature flag — specifically an operational (ops_) flag designed to disable a feature or code path immediately in a production incident, without a deploy. All kill switches are feature flags; not all feature flags are kill switches. Kill switches are typically permanent and kept “on” under normal conditions, with the ability to flip them “off” as an emergency circuit breaker.

What does “toggle” mean in software?

In computing, “toggle” means to switch between two states — on and off. A toggle switch on a UI flips between enabled and disabled. In the context of feature flags, “toggling” a feature means switching it from enabled to disabled (or vice versa) for a set of users. The term comes from electronics, where a toggle switch is a physical binary switch.