> Markdown version of [/@justin-halsall](https://www.wearedevelopers.com/@justin-halsall). Every page supports `.md` or `Accept: text/markdown`. Links point to the HTML versions so they work for humans too. Agent guide: [/agents.md](https://www.wearedevelopers.com/agents.md).

---

# Justin Halsall
Builds open-source session replay tools at rrweb and hosts the CODE100 coding game show.

## About

Justin Halsall builds tools that let developers see exactly how users interact with their software. He maintains the open-source session replay library rrweb and co-founded Kilo Code.

He focuses on bridging the gap between code deployment and user reality, especially in making session data usable for AI agents. On stage, Justin dissects the psychology of [live coding competitions](/videos/2132-wearedevelopers-live-code100-at-wearedevelopers-europe) and hosts [satirical tech news panels](/videos/1843-humanoid-runs-wild-google-rewrites-headlines-and-slow-ai-justin-halsall-and-schepp) that test audiences on bizarre industry headlines.

Outside of his startup work, he contributes to the Apache Software Foundation.


## Upcoming Sessions

### World Congress 2026 North America · September 23, 2026
San José, CA
- [Closing the autonomous software development loop](https://www.wearedevelopers.com/events/world-congress-2026-north-america/sessions/1932-closing-the) · 30 min




## WeAreDevelopers LIVE

- [WeAreDevelopers LIVE - CODE100 at WeAreDevelopers Europe](https://www.wearedevelopers.com/videos/2132-wearedevelopers-live-code100-at-wearedevelopers-europe) · Chris Heilmann, Daniel Cranney, Justin Halsall, Werner Jeschko, Nicole Jeschko, Mirco Tomić
- [WeAreDevelopers LIVE - CSS is DOOMed](https://www.wearedevelopers.com/videos/1838-wearedevelopers-live-css-is-doomed) · Chris Heilmann, Daniel Cranney, Justin Halsall, Christian Schaefer
- [Humanoid Runs Wild, Google Rewrites Headlines and Slow AI - Justin Halsall and Schepp](https://www.wearedevelopers.com/videos/1843-humanoid-runs-wild-google-rewrites-headlines-and-slow-ai-justin-halsall-and-schepp) · Chris Heilmann, Daniel Cranney, Justin Halsall, Christian "schepp" Schaefer


## Links

- [X](https://x.com/juice10)
- [LinkedIn](https://www.linkedin.com/in/juice10)
- [Blog](https://substack.com/@justinhalsall)