Vercel Labs' portless replaces localhost port numbers with named URLs specifically so agents stop testing the wrong port.

12,094 stars under Apache-2.0, last release v0.15.6 on August 24. A local proxy on port 1355 maps named hosts like myapp.localhost onto ephemeral internal ports, and the README names "agents testing the wrong port" as a target failure mode. Ships its own agent skill and an AGENTS.md. Setting --tld to a domain you own makes local URLs structurally match production, keeping OAuth redirects and cross-subdomain cookies consistent across both. GitHub