Python typing got fast enough to feel invisible. Pyrefly is a new, open source type checker and IDE language server from Meta, written in Rust, with a focus on instant feedback and real-world DX. Today, we will dig into what it is, why it exists, and how it plays with the rest of the typing ecosystem. We have Abby Mitchell, Danny Yang, and Kyle Into from Pyrefly here to dive into the project. 
 
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<h2 class="links-heading mb-4">Links from the show</h2>
<div>Abby Mitchell: <a href="https://www.linkedin.com/in/abby-mitchell/?featured_on=talkpython" target="_blank" >linkedin.com</a> 
Danny Yang: <a href="https://www.linkedin.com/in/yangdanny97/?featured_on=talkpython" target="_blank" >linkedin.com</a> 
Kyle Into: <a href="https://www.linkedin.com/in/kyleinto/?featured_on=talkpython" target="_blank" >linkedin.com</a> 
 
Pyrefly: <a href="https://pyrefly.org?featured_on=talkpython" target="_blank" >pyrefly.org</a> 
Pyrefly Documentation: <a href="https://pyrefly.org/en/docs/?featured_on=talkpython" target="_blank" >pyrefly.org</a> 
Pyrefly Installation Guide: <a href="https://pyrefly.org/en/docs/installation/?featured_on=talkpython" target="_blank" >pyrefly.org</a> 
Pyrefly IDE Guide: <a href="https://pyrefly.org/en/docs/IDE/?featured_on=talkpython" target="_blank" >pyrefly.org</a> 
Pyrefly GitHub Repository: <a href="https://github.com/facebook/pyrefly?featured_on=talkpython" target="_blank" >github.com</a> 
Pyrefly VS Code Extension: <a href="https://marketplace.visualstudio.com/items?itemName=meta.pyrefly&featured_on=talkpython" target="_blank" >marketplace.visualstudio.com</a> 
Introducing Pyrefly: A New Type Checker and IDE Experience for Python: <a href="https://engineering.fb.com/2025/05/15/developer-tools/introducing-pyrefly-a-new-type-checker-and-ide-experience-for-python/?featured_on=talkpython" target="_blank" >engineering.fb.com</a> 
Pyrefly on PyPI: <a href="https://pypi.org/project/pyrefly/?featured_on=talkpython" target="_blank" >pypi.org</a> 
InfoQ Coverage: Meta Pyrefly Python Typechecker: <a href="https://infoq.com/news/2025/05/meta-pyrefly-python-typechecker/?featured_on=talkpython" target="_blank" >infoq.com</a> 
Pyrefly Discord Invite: <a href="https://discord.gg/Cf7mFQtW7W?featured_on=talkpython" target="_blank" >discord.gg</a> 
Python Typing Conformance (GitHub): <a href="https://github.com/python/typing/tree/main/conformance?featured_on=talkpython" target="_blank" >github.com</a> 
Typing Conformance Leaderboard (HTML Preview): <a href="https://htmlpreview.github.io/?https://github.com/python/typing/blob/main/conformance/results/results.html&featured_on=talkpython" target="_blank" >htmlpreview.github.io</a> 
 
Watch this episode on YouTube: <a href="https://www.youtube.com/watch?v=P4RKxl_giH4" target="_blank" >youtube.com</a> 
Episode #523 deep-dive: <a href="https://talkpython.fm/episodes/show/523/pyrefly-fast-ide-friendly-typing-for-python#takeaways-anchor" target="_blank" >talkpython.fm/523</a> 
Episode transcripts: <a href="https://talkpython.fm/episodes/transcript/523/pyrefly-fast-ide-friendly-typing-for-python" target="_blank" >talkpython.fm</a> 
 
Theme Song: Developer Rap 
🥁 Served in a Flask 🎸: <a href="https://talkpython.fm/flasksong" target="_blank" >talkpython.fm/flasksong</a> 
 
---== Don't be a stranger ==--- 
YouTube: <a href="https://talkpython.fm/youtube" target="_blank" > youtube.com/@talkpython</a> 
 
Bluesky: <a href="https://bsky.app/profile/talkpython.fm" target="_blank" >@talkpython.fm</a> 
Mastodon: <a href="https://fosstodon.org/web/@talkpython" target="_blank" > @talkpython@fosstodon.org</a> 
X.com: <a href="https://x.com/talkpython" target="_blank" > @talkpython</a> 
 
Michael on Bluesky: <a href="https://bsky.app/profile/mkennedy.codes?featured_on=talkpython" target="_blank" >@mkennedy.codes</a> 
Michael on Mastodon: <a href="https://fosstodon.org/web/@mkennedy" target="_blank" > @mkennedy@fosstodon.org</a> 
Michael on X.com: <a href="https://x.com/mkennedy?featured_on=talkpython" target="_blank" > @mkennedy</a> </div>

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