Glean is a modern approach for a telemetry library and is part of the Glean project.

Glean logo

There are two implementations of Glean, with support for 5 different programming languages in total. Both implementations strive to contain the same features with similar, but idiomatic APIs.

Unless clearly stated otherwise, regard the text in this book as valid for both clients and all the supported programming languages and environments.

The Glean SDK

The Glean SDK is an implementation of Glean in Rust, with language bindings for Kotlin, Python, Rust and Swift.

For development documentation on the Glean SDK, refer to the Glean SDK development book.

To report issues or request changes on the Glean SDK, file a bug in Bugzilla in Data Platform & Tools :: Glean: SDK.


Glean.js is an implementation of Glean in JavaScript. Currently, it only has support for usage in web extensions.

For development documentation on Glean.js, refer to the Glean.js development documentation.

To report issues or request changes on Glean.js, file a bug in Bugzilla in Data Platform & Tools :: Glean.js.

Note Glean.js is still in development and does not provide all the features the Glean SDK does. Feature parity will be worked on after initial validation. Do not hesitate to file a bug if you want to use Glean.js and is missing some key Glean feature.


User Guides

This section of the book contains mostly step-by-step guides and essays detailing how to achieve specific tasks with Glean.

It contains guides on the first steps of integrating Glean into your project, choosing the right metric type for you, debugging products that use Glean and Glean's built-in error reporting mechanism.

If you want to start using Glean to report data, this is the section you should read.

API Reference

This section of the book contains reference pages for Glean’s user facing APIs.

If you are looking for information a specific Glean API, this is the section you should check out.

Language Binding Information

This section contains guides and essays regarding specific usage information and possibilities in each of Glean's language bindings.

Check out this section for information on the language binding you are using.



In this book we use a lot of Glean specific terminology. In the glossary, we go through many of the terms used throughout this book and describe exactly what we mean when we use them.


This section contains detailed notes about changes in Glean, per release.

This Week in Glean

“This Week in Glean” is a series of blog posts that the Glean Team at Mozilla is using to try to communicate better about our work. They could be release notes, documentation, hopes, dreams, or whatever: so long as it is inspired by Glean.

Contribution Guidelines

This section contains detailed information on where and how to include new content to this book.


To contact the Glean team you can:

  • Find us in the #glean channel on
  • Send an email to
  • The Glean SDK team is: :janerik, :dexter, :travis, :mdroettboom, :gfritzsche, :chutten, :brizental.


Glean.js and the Glean SDK Source Code is subject to the terms of the Mozilla Public License v2.0. You can obtain a copy of the MPL at