Feature Flag

A feature flag is a code-level toggle that lets a development team turn a feature on or off — or show it to only a subset of users — without deploying new code. Originally a software engineering tool for safer releases, feature flags are also used for experimentation: showing a new feature to half of users and comparing outcomes against the other half.

Feature-flag infrastructure is a genuinely different, more technical capability than a marketer-friendly visual page editor — it requires real engineering involvement to set up and use well, which is part of why tools built around it (like Optimizely) skew toward engineering-led organizations rather than marketing teams working independently.

Central to our Optimizely review, where feature-flag depth is described as the tool's genuine strength versus VWO's more marketer-accessible visual editor approach.