Parity

Parity rebuilds old business software as a modern web app and proves the new app does exactly what the old one did, field by field. It watches someone use the old app and talk about it, explores the app on its own, and writes its business rules in plain language with evidence for an expert to confirm. Muse Code rebuilds it; Parity replays the same scenarios on both apps and compares every field in plain code until they match. The proof stays: a GitHub Action replays it on every pull request, and a coding agent can call it over MCP. On Virtual Salesman 3, a 2006 Windows app, it caught a rebuild one cent off (69.21 against 69.22) and proved the corrected one, 8 of 8 fields, for $0.46. On FrontAccounting, an app nobody on the team wrote, fuzzing against the live app found differences the recording never showed, shrank each to one line, and one repair closed them. Migration mode rebuilt three screens on records read through the old app's own forms, each proved (28/28, 113/113, 258/258 fields). A three-step page, Rebuild an app, takes anyone from an address and a login to rebuilt screens in a modern template, each proved, with the price shown before anything is spent. Try it in two minutes with no API key: git clone https://github.com/GlamgarOnDiscord/parity-agent.git && cd parity-agent && bun install && bun run prove Landing page: https://glamgarondiscord.github.io/parity-agent/