Why is my local version not matching the hosted version
Published on: Fri Jul 17 2026
Yesterday, I had the pleasure of tackling a very confusing bug.
My web app (cl-viz.app) has two versions, a version that is hosted on Cloudflare and a version that you can run locally. As should be the case, identical in all respects. Except that you needed one extra step for the local version, launch a simple python server.
Given this, I was surprised that the local version of the app was behaving differently from the web version for the same inputs. My first suspicion was that the files packaged for the local version was stale. So, that took me down a path which reached a dead end. All the files were exactly the same, as should be the case.
My dev setup was working off tiny samples which showed same output on both the web and local versions. So, I didn’t have much to go on.
On my prod setup, I then started a debugging process by isolating the input lines by chunks to see which lines were triggering this behaviour. Once I managed to isolate the problem lines, I was able to replicate the same on my dev setup. Now that I had something tangible to work with, I fed that to 5.6 Sol(medium). It ran some tests and figured out the reason for the discrepancy. There was bug in the program that surfaced only when a specific user setting was enabled. The local version of the app shipped with that setting enabled whereas the web version had it turned off. The app uses browser local storage for everything including user preferences. I had turned off the setting for the web version long ago and that’s why it did not surface the bug.
So, that was it - a user setting that I had forgotten about.
Would I have found it without help from Sol? Maybe, but it would have taken much longer.
Interesting times ahead.