> ## Documentation Index
> Fetch the complete documentation index at: https://cordial.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# Changing FastFlags
> Set Roblox FastFlags in Cordial, see which layer wins, and find the flags and keys Cordial itself reads.
FastFlags are Roblox's internal tuning switches. Cordial lets you override any of them, per profile, from a file or from **Settings → FastFlags**.
## Set a flag
**Settings → FastFlags** is a text editor for your profile's `flags.json`. Paste a list, or type one, and press **Apply**.
```json theme={null}
{
"DFFlagRbxTransportUseRtcioRna": false,
"FIntTaskSchedulerAutoThreadLimit": 8,
"FFlagDebugGraphicsDisableVulkan": false
}
```
Values can be booleans, numbers or strings. Roblox stores them all as strings and Cordial converts. The format is Bloxstrap's, so a list from a video or a Discord message pastes in as it is.
The editor says it applies the next time you press Roblox. A `DF` flag can also change in a game that is already running; see [When a change takes effect](#when-a-change-takes-effect).
To edit the file yourself, it is one file per profile:
```text theme={null}
~/.local/share/cordial/profiles//flags.json
```
```text theme={null}
~/.var/app/io.github.luohoa97.Cordial/data/cordial/profiles//flags.json
```
`INFERRED` from how Flatpak remaps `XDG_DATA_HOME`; not checked against an installed package. The editor prints the real path under the text box.
`CORDIAL_FLAGS` points the client at another file. It makes one file serve every profile, so it is for experiments.
A name the engine does not know is accepted and ignored, silently. An invented flag looks exactly like a working one. If a flag seems to do nothing, check that it exists:
```bash theme={null}
strings ~/.cache/cordial/lib/x86_64/libroblox.so | grep -x DebugGraphicsDisableVulkan
```
The file carries the `FFlag`/`FInt`/`FString` prefix; the engine's own table stores the name without one, which is why the `grep` drops it.
To choose a graphics backend, use **Settings → General → Graphics**, not a flag. Cordial decides that before the engine starts.
## When a change takes effect
| Flag family | When it is read |
| - | - |
| `FFlag`, `FInt`, `FString` | Once, at startup. Relaunch to change them. |
| `DFFlag`, `DFInt`, `DFString` | At startup, and again while the game runs: Roblox re-fetches its settings about every two minutes and Cordial hands the engine your overrides again straight after. |
A plugin loaded part-way through a session cannot change a startup flag, whatever it writes.
Cordial puts your overrides back after each Roblox refresh, whatever the family. Each time it prints a `[reapply]` line with what it cost. Two limits:
* The first couple of seconds, before the engine's first fetch, are not covered.
* It re-sends the cached copy of Roblox's document, so a flag Roblox changed during your session goes back to its older value, as at launch.
`CORDIAL_NO_FLAG_REDELIVERY=1` in the client's environment turns the re-apply off. It exists to confirm that a flag reverts without it.
Why: [ADR-051](/adr/ADR-051-overrides-are-reapplied-after-the-engines-refresh).
## Which layer wins
Flags come from several sources and each owns its own file. From lowest precedence to highest:
| Layer | Source | Notes |
| - | - | - |
| Roblox's settings | The client-settings document from Roblox | The base everything else is merged into. |
| Cordial's default | Built in | Only `FFlagUserLaunchedWithBloxstrap`, see the table below. |
| Graphics optimisation | **Settings → General → Graphics** | The "more cores" and "fewer cores" choices set thread-count flags. Balanced sets none. |
| Plugins | `/flags.json`, alphabetical | A plugin switched off contributes nothing. |
| Frame rate limit | **Settings → General → Graphics** | Sets `DFIntTaskSchedulerTargetFps`. Beats a plugin that sets the same flag. |
| Your flags | `/flags.json` | Always wins. |
A plugin never writes to your file. Removing a plugin removes its flags, and when two layers set the same flag the log names both:
```text theme={null}
flags: FIntTaskSchedulerAutoThreadLimit = 8 from user
(overrides plugin:fps-tweaks=4, plugin:net-tuner=16)
```
Two plugins that disagree are both named. The later one wins so the outcome is deterministic.
Your flags live in the profile, so a flag you set while testing on one account is not still set on the account you play. A file left at the old `~/.config/cordial/flags.json` is moved into the first profile that looks for one ([ADR-013](/adr/ADR-013-per-profile-configuration)). The layering itself: [ADR-005](/adr/ADR-005-flag-service).
## Flags and keys Cordial reads
Besides Roblox's own flags, these names mean something to Cordial. The `Cordial` ones are never sent to Roblox.
| Name | Values | What it does |
| - | - | - |
| `FFlagUserLaunchedWithBloxstrap` | `True` (default) | Tells games the launcher speaks BloxstrapRPC, which Discord presence needs. Set `"False"` to retract the claim; games can then tell they are not under a launcher that implements it. It is not an engine flag. That a game then answers yes is `INFERRED`. |
| `DFIntTaskSchedulerTargetFps` | whole number | The engine's own frame target. **Settings → General → Graphics → Frame rate limit** sets it for you. |
| `CordialFrameRateLimit` | `display`, or a number of fps | The Frame rate limit row, as a key a plugin can set. The row beats a plugin; your `flags.json` beats the row. |
| `CordialPresentMode` | `off`, `auto`, `mailbox`, `immediate`, `uncapped`, `fifo`, `fifo-relaxed` | Vulkan present mode. The **Frame pacing** row sets it. A mode the driver does not offer leaves the engine's own choice. |
| `CordialGraphicsBackend` | `automatic`, `vulkan`, `gles` | Which graphics backend to offer the engine. The **Graphics** row beats a plugin's request. |
| `CordialDeviceProfile` | `pc-windows-11`, `roblox-app`, `android-tablet`, `meta-quest` | Which device Cordial says it is. **Has no effect from `flags.json` today**; the Graphics optimisation row sets it, through `CORDIAL_DEVICE_PROFILE`. `INFERRED` from reading the code: nothing outside the flag module calls the reader. |
Graphics optimisation sets these flags, sized to your physical core count:
"Windows PC - more cores" (`CORDIAL_PERFORMANCE=throughput`):
| Flag | Value |
| - | - |
| `FIntTaskSchedulerThreadMin` | `0` |
| `FIntTaskSchedulerAsyncTasksMinimumThreadCount` | physical cores, at most 3 |
| `FIntTaskSchedulerAutoThreadLimit` | physical cores |
| `FIntSmoothClusterTaskQueueMaxParallelTasks` | physical cores |
| `FIntOcclusionWorkerThreadCount` | half the physical cores, rounded up |
| `FFlagMovePrerenderV2` | `True` |
| `FFlagGcInParallelWithRenderPrepare3` | `True` |
| `DFIntSimMidPhaseContactPipelineBatchSize` | `128` |
"Windows PC - fewer cores" (`CORDIAL_PERFORMANCE=latency`) sets only `DFIntSimMidPhaseContactPipelineBatchSize` to `128` and `FIntTaskSchedulerThreadMin` to `0`.
None of these is measured on this project's hardware, which is why Balanced, which sets nothing, is the default.
## Raise the frame rate
The Android client has no frame-rate row in its own menu, so there are two separate levers in Cordial's Settings.
| What you want | Where |
| - | - |
| Stop drawing being pinned to your display's refresh | **Settings → General → Graphics → Frame pacing**. Mailbox is the default. The FPS Flex plugin pulls the same lever, so use one or the other. |
| Raise the engine's own target frame rate and keep it there | **Settings → General → Graphics → Frame rate limit** |
Neither replaces the other. Frame pacing on FIFO caps you at your panel's rate whatever the limit says. Frame pacing applies at the next launch.
**Frame rate limit** offers Display refresh (sets nothing), or 90, 120, 144, 165 or 240. A new cap takes effect in a running game at once. Going back to Display refresh takes up to two minutes, because the engine does not unset a flag that Roblox's settings leave out.
Do not pick a cap above your display's refresh. On a 60 Hz output a cap of 90 presented about 31 frames a second and 240 about 36, against 57 to 60 with nothing set. That is one headless environment, and on a fast monitor the opposite holds: on a 240 Hz output with an NVIDIA GPU, `DFIntTaskSchedulerTargetFps=240` presented 216-232 frames a second against a flat 59.9 with the engine's own target (measured 2026-10-03). Nothing above 240 is offered because a contributor reports the engine stops there.
## Import a list from another launcher
**Settings → FastFlags → Import…** reads a Bloxstrap or Fishstrap `ClientAppSettings.json`, or Sober's `config.json` (only its `fflags` object), and merges the flags into this profile's. From a terminal:
```bash theme={null}
cordial --import-flags ClientAppSettings.json # or - for standard input
cordial --import-flags --sober # finds Sober's own config
cordial --import-flags list.json --profile NAME --replace
```
Flags already set are kept unless the list sets them again. `--replace` starts from empty instead. Values are checked by prefix: `FFlag` takes `True` or `False`, `FInt` a whole number, and `FLog` anything, because a log channel takes either a number or a severity and that is not visible from outside.
An entry the check refuses is skipped and named, and the rest are imported. A name with no FastFlag prefix is imported and listed, so a typo shows. The Sober path outside the Flatpak (`~/.config/sober/config.json`) is `INFERRED`; only the Flatpak's has been seen.
## If the interface looks coarse
The interface is laid out for a low-density phone: render resolution is 720p and `dpiScale` is 1.0. For a direct `cordial-run` launch, raise both:
```bash theme={null}
CORDIAL_MONITOR=1 CORDIAL_RESOLUTION=1920x1200 CORDIAL_DPI_SCALE=1.75 \
cordial-run --lib-dir /path/to/lib/x86_64 --apk /path/to/base.apk \
--host-libc --game-activity --run 30
```
Roblox's graphics-quality flags (`DebugFRMQualityLevelOverride` and the MSAA overrides) change nothing here, because they govern 3D scenes and the signed-out landing page is a 2D interface.
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