Feature Flag

A switch in the code that turns a feature on or off without a new deployment, letting teams release to some users, run tests, or roll back instantly.

Why it matters

Feature flags let you ship safely and continuously, releasing to a few users first and killing a broken feature in seconds. They are a foundation of modern, low-risk shipping.

For example

The team ships a new checkout behind a feature flag, turns it on for 5 percent of users, and flips it off in seconds when errors spike.

Go deeper

Feature Toggles (aka Feature Flags) martinfowler.com · article Flags let you merge and deploy unfinished or risky work while keeping it switched off, so you avoid long lived branches and can turn a bad feature off without a redeploy. That is a cheap safety net that fits two people and removes a lot of the fear that pushes founders toward heavy process. This piece covers the useful patterns and the ones that create mess later. Open martinfowler.com →

Related terms

Also in Starting Up

See how founders actually handle this on Building the product, part of the Starting Up hub.

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