What Made This Possible

Building AI features in a browser is not the same as building AI features in a standalone app or a cloud service. The constraints are different. You have limited resources, strict privacy requirements, and the need to work across Windows, macOS, and Linux. Here is what made it work:

Starting small: We did not try to build everything at once. The first runtime was minimal. The first model was simple. We added complexity only when we needed it.

Privacy as a requirement, not a feature: Every decision started with “can this run locally?” If the answer was no, we either changed the approach or did not build it.

Reusable infrastructure: We built the runtime once and used it for multiple features. That meant each new AI capability got cheaper to ship.

Learning from real users: The validation app for PDF.js alt text was not just about improving the model—it was about understanding what real people needed. User feedback drove every iteration.