Vercel Labs has open-sourced portless, a reverse proxy that replaces localhost:3000 with stable, named URLs like https://myapp.localhost. Simply run portless run next dev (or whatever dev command you use) and your app is reachable at a neat URL with zero config. It assigns ephemeral ports behind the scenes, so multiple dev servers don’t conflict because they are using the same ports (it passes URL and PORT as env variable to the dev server).
Portless can also auto-detect git worktrees and gives each branch its own subdomain (fix-ui.myapp.localhost), which eliminates port clashes when you're reviewing code across multiple branches simultaneously. No more Agents fighting each other on what they think is “their” site!
HTTPS is also supported transparently by generating a local Certificate Authority on first run: no browser warnings, no mismatch between your local environment and production.
Many frameworks are supported out of the box and Portless runs on macOS, Linux, and Windows.
One pnpm install -g portless to get started (it now works locally as well, e.g. vp i -D portless for those of you using vite-plus already).