You'll noticeTier: how much it should matter to you
4Useful: my rating, 1 to 5
2Signal: worth watching, 1 to 5
MCPArea: what it touches
Bug FixesKind: in v2.1.229,
What probably matters to youSection of the release
What
When an MCP server signs you in through your browser, the local address it redirects back to is now http://127.0.0.1 rather than http://localhost. This fixes sign-in on machines where localhost resolves to the IPv6 address ::1 and nothing is listening there.
Details
Servers you have already signed into keep working: the check that reuses a previously registered redirect address now accepts either origin, where it used to demand http://localhost exactly.
The port is still chosen at runtime and filled into the address.
Evidence
t === "http://127.0.0.1" || t === "http://localhost"
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
How sure we are
One source agreesOne thing we can check says the same as this entry.
Anthropic's release notes agreeFixed MCP OAuth with strict authorization servers by using 127.0.0.1 instead of localhost in the redirect URI
