JTL Lens
A local-first utility for comparing two JMeter test results — two JTL files, one comparison, a clearer discussion.
The problem
Comparing two high-concurrency performance tests by hand: open spreadsheets, compare metrics, calculate differences, explain them, double-check them — then repeat the same exercise with developers and operations until everyone agrees what actually changed. Not hard. Just painfully repetitive.
The approach
I first prototyped it with Lovable, mostly out of curiosity: upload two JTL files, click Compare, done. It held up on a handful of JTLs.
The decision that mattered
A public, hosted prototype isn’t something I was comfortable running real test data through. So I rebuilt it as a local-first tool that runs entirely on my own machine, with no files ever leaving it. Same core idea, actually usable for real work.
What changed
The biggest value was never the few minutes saved. Instead of debating numbers, teams started discussing why the numbers changed — everyone looking at the same report. The question moved from “whose numbers are correct?” to “what changed in the system?”
What I took from it
Sometimes the best use of AI is astonishingly simple: remove one repetitive task, reduce one source of friction, give engineers back their thinking time.
A personal project, independent of my employer.