What Language Is Slack Written In?

What Language Is Slack Written In

If you’ve used Slack, you appreciate how convenient the platform is for team collaboration.

There is plenty you can achieve when using Slack and most organizations rely on Slack to connect with their employees, especially when working on projects.

Everything about Slack, from its user interface to how it handles data, is amazing and begs the question of what language Slack is written in.

Quick Answer

For its backend, Slack was initially written in PHP. However, it later dropped PHP and adapted Hacklang, which offered a better way of enhancing productivity by offering better tools for its developers to increase workflow.

Its desktop application is written in the Electron framework, enabling Slack to be a cross-platform application.

For the Android application, Slack utilizes Kotlin and Java, but for iOS, it relies on Swift and Objective-C.

This guide discusses the languages that Slack is written in. We will check the languages used for the backend and frontend. That way, we will see Slack’s transition since its launch.

What Language is Slack Written In?

Slack is designed as an all-in-one collaboration tool, and offers multiple features to facilitate team collaboration. As a developer, you can get curious to know what language Slacks uses for its applications to create impressive user interfaces, mobile applications, and its backend.

Here’s the thing, Slack launched in 2014, and it used PHP 5 for its backend. PHP was a popular server-side language at that time, and like most companies, Slack ended up using it for its backend applications.

However, Slack switched to HHVM in 2016 to replace PHP, as with HHVM. Slack could utilize Hack/Hacklang for the backend applications.

Unlike PHP, Hack enhanced the speed and productivity of Slack developers thanks to its various tooling options. Besides, Hack has a better static type checker, meaning developers can quickly catch bugs in the code and add to their confidence when coding.

Moreover, Hack proved a better backend alternative as its type checking is done statically without running the code. That way, developers can quickly find errors before saving the code.

For the Slack web application, the platform is written in JavaScript and React framework. To achieve cross-platform usage, Slack resorted to using the Electron framework for its desktop applications. The Electron aka Atom Shell, facilitates a frameless and faster development of applications.

Slack is also available as a mobile application for Android and iOS. Slack uses Java and Kotlin for the Android application. For the iOS Slack application, it uses Swift and Objective-C. The discussed are the prominent languages that Slack is written with. Note that other languages are used, but they fall under the main ones we’ve mentioned.


Slack is a comprehensive application available as a web, desktop, and mobile application.

Slack mainly runs on Hacklang for its backend.

For desktop applications, it uses the Electron framework.

The web application uses JavaScript and React for the interfaces.

For mobile, it runs on Java on Kotlin for Android and Swift combined with Objective-C for iOS.

Frequently Asked Questions

Does Slack still use PHP?

Slack’s official article confirmed that it shifted from using PHP for its backend and now uses Hacklang as it offers more productivity and better debugging than PHP. Slack migrated to using Hacklang in 2016.

What languages does Slack use for its UI?

The web application UI is based on React framework and JavaScript. However, Slack utilizes the Electron framework for desktop applications.

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