Which programming language does Meta (Facebook) use?
Facebook (now Meta) is primarily written in Hack, Meta's typed dialect of PHP, on the backend, with C++ for performance-critical systems, Python for data and ML work, and JavaScript with React on the front end. There is no single "Facebook language": each product picks the right tool.
Here are the main programming languages Facebook and Meta use, and where each one runs:
1. Hack (Facebook's PHP)
- Core language: Facebook was originally built in PHP. Over time, the company developed Hack, a language that builds on PHP and adds static typing and major performance improvements, running on Meta's own HHVM virtual machine.
- Usage: The core of the Facebook web application is still written in Hack. This is the closest thing to "the language Facebook is written in."
- Source: Hack: Programming Language
2. C++
- Usage: Meta uses C++ for high-performance backend systems where efficiency is crucial, such as the news feed ranking infrastructure, Messenger backend services, and core infrastructure.
- Source: Meta Engineering
3. Python
- Usage: Python powers data science, machine learning, and automation at Meta, including much of Instagram's backend (which famously runs one of the world's largest Django deployments). PyTorch, Meta's open-source deep learning framework, has a Python-first interface.
- Source: Python at Meta
4. Java
- Usage: Java runs backend services, particularly large-scale distributed systems and parts of the Android ecosystem (alongside Kotlin).
5. JavaScript and React
- Usage: Meta created and open-sourced React, the JavaScript library that powers the user interfaces of Facebook and Instagram, and React Native for cross-platform mobile apps.
- Source: React
6. Objective-C and Swift
- Usage: Meta's iOS apps (Facebook, Messenger, Instagram) are built with Objective-C and, increasingly, Swift.
7. Erlang (WhatsApp)
- Usage: WhatsApp's messaging servers were famously built in Erlang, chosen for its massive concurrency support, and Meta kept that architecture after acquiring WhatsApp.
Language by Product
| Product / area | Main languages |
|---|---|
| Facebook web backend | Hack (PHP dialect) |
| News feed, infrastructure | C++ |
| Instagram backend | Python (Django), C++ |
| WhatsApp servers | Erlang |
| Machine learning / AI | Python (PyTorch), C++ |
| Web front end | JavaScript, TypeScript, React |
| Mobile apps | Swift, Objective-C, Kotlin, Java, React Native |
Which Language Should You Use in a Meta Interview?
Meta's coding interviews are language-agnostic: you can interview in Python, C++, Java, JavaScript, or almost any mainstream language. Most candidates pick Python for its speed of writing under time pressure. Interviewers grade your problem-solving patterns, data structures, and communication, not your language choice. If you are preparing, our guide to the top 20 coding questions to pass the Meta interview shows exactly what gets asked, and Grokking the Coding Interview teaches the patterns behind those questions.
Frequently Asked Questions
Is Facebook still written in PHP?
Effectively no. Facebook migrated from plain PHP to Hack, its own statically typed PHP dialect running on the HHVM virtual machine. The syntax family survives, but modern Facebook code is Hack, not vanilla PHP.
What language is Instagram written in?
Instagram's backend is mainly Python built on Django, with performance-critical pieces in C++. The apps use Swift/Kotlin and React Native.
What database does Facebook use?
Facebook uses MySQL at enormous scale, fronted by TAO (its social-graph cache) and RocksDB, plus many specialized internal storage systems.
Summary
Meta uses a diverse set of programming languages: Hack and C++ for the backend, Python for data and AI, Erlang for WhatsApp, and JavaScript with React for the front end. For interview preparation, pick the language you are fastest in; what Meta tests is how you solve problems, not which language you type them in.
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