{"version":"2.1.229","anchor":"mcp-sign-in-callback-now-uses-127-0-0-1","canonical_anchor":"mcp-sign-in-callback-now-uses-127-0-0-1","heading":"MCP sign-in callback now uses 127.0.0.1","tier":"notice","area":"MCP","scope":null,"heads_up":null,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.229\/e\/mcp-sign-in-callback-now-uses-127-0-0-1","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.229","markdown":"### MCP sign-in callback now uses 127.0.0.1\n\nMCP browser sign-in now redirects to 127.0.0.1, fixing failures on IPv6-only localhost setups.\n\n**What**\n\nWhen 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.\n\n**Details**\n\n- 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.\n- The port is still chosen at runtime and filled into the address.\n\n**Evidence**\n\n`t === \"http:\/\/127.0.0.1\" || t === \"http:\/\/localhost\"`\n\n- Area: MCP\n- Tier: You'll notice\n- Useful: 4\/5\n- Signal: 2\/5"}