What Are Roblox Fast Flags?

A Fast Flag (FFlag) is a piece of Roblox's internal client configuration — a switch or a tunable value that Roblox itself uses to turn features on and off, run gradual rollouts, and A/B test changes without shipping a new client build. They're not a cheat code or a hidden menu; they're the same mechanism Roblox's own engineers use, and a small number of them happen to be safe for a player to change too.

The naming prefixes

Every flag's name tells you its data type and whether it can change without a client update:

  • FFlag / DFFlag — a boolean (on/off) switch. The D means "dynamic": Roblox can flip it server-side without pushing a new client.
  • FInt / DFInt — a whole-number value, e.g. DFIntTaskSchedulerTargetFps, which sets a target frame rate for the task scheduler.
  • FString / DFString — free text, often URLs or config strings for internal services.
  • FLog / DFLog — a verbosity level for internal logging, typically 0-7.

Not every flag fits this pattern exactly — Roblox's naming isn't a strict spec — but it covers the large majority of what you'll see in the database.

Why players use them

A small, curated set of flags happen to control things players care about: frame rate targets, shadow rendering cost, network replication rate, on-screen debug overlays. Setting FIntRenderShadowIntensity to 0 removes visible shadows entirely, for example — a real, verified effect, not a guess.

The 2025 allowlist change

Since late September 2025, the Roblox client only accepts local FastFlag overrides (ClientAppSettings.json) for flags on Roblox's own official allowlist — anything else is silently ignored. This is why some tools on our tools page are marked Non Risk: they only ever touch allowlisted flags, so there's no way to misconfigure something outside that list through them. Other tools bypass this by injecting flags at a different level, which is why they carry an actual risk rating instead.

Next steps

Ready to apply some? Read how to use Fast Flags, browse flags by category, or let the generator build a config from a plain-English description.