OSS
Vercel Labs' portless replaces localhost port numbers with named URLs specifically so agents stop testing the wrong port
portless is at 12,094 stars under Apache-2.0, last released v0.15.6 on 2026-08-24, and runs a local proxy on port 1355 that maps named hosts like myapp.localhost onto ephemeral internal ports. The README names 'agents testing the wrong port' as a target failure mode, and the repo ships its own agent skill at skills/portless plus an AGENTS.md. Setting --tld to a domain you own makes local URLs structurally match production, which keeps OAuth redirects and cross-subdomain cookies working the same in both.
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