Project NameLanguage BindingsOperating SystemApp Lifecycle TypeEnvironment Data source
glean-preview1RustWindows/Mac/LinuxDesktop applicationOS info build-time autodetected, app info passed in
Glean AndroidKotlin, JavaAndroidMobile appAutodetected from the Android environment
Glean iOSSwiftiOSMobile appAutodetected from the iOS environment
Glean.pyPythonWindows/Mac/LinuxallAutodetected at runtime
FOG2Rust/C++/JavaScriptas Firefox supportsDesktop applicationOS info build-time autodetected, app info passed in

Features matrix

Core metric typesX
Metrics Testing APIX
baseline pingXXX
deletion-request ping
Custom pingsX
Custom pings testing APIXX
Debug Ping View support


glean-preview is an experimental crate for prototyping integration into Firefox. It it not recommended for general use. See Project FOG.


Firefox on Glean (FOG) is the name of the layer that integrates the Glean SDK into Firefox Desktop. It is currently being designed and implemented. It is being used as a test bed for how best to write a generic Rust language binding layer and so temporarily ties directly to glean-core instead of an API crate. Prospective non-mozilla-central Rust consumers of the Glean SDK should not follow its example and should instead follow bug 1631768 for updates on when the proper language binding crate will be available.