[BUG] Claude.ai crashes immediately when adding Remote MCP Server URL

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Bug Description

When adding a Remote MCP Server in claude.ai (Settings > Connectors), pasting any URL into the "Remote MCP Server URL" field immediately crashes the page with:

> "Claude will return soon — Claude is currently experiencing a temporary service disruption. We're working on it, please check back soon."

The crash happens instantly when the URL is pasted, before any "Add" button is clicked.

## Steps to Reproduce

1. Go to https://claude.ai/settings/connectors
2. Click "Add" next to "Remote MCP Servers"
3. Paste a URL (e.g. https://unclestock.com/mcp) into the URL field
4. Page immediately crashes

## Expected Behavior

The URL should be accepted and Claude should proceed with OAuth discovery / connection setup.

## Actual Behavior

The entire claude.ai page crashes and shows the "Claude will return soon" error page.

## Environment

• Browser: Google Chrome version 122.0.6261.129 (Officiële build)
• OS: Windows 11
• This is about claude.ai web app, not Claude Code CLI or Claude Desktop

## Notes

• The MCP server at the URL is functional and responds correctly to /.well-known/oauth-authorization-server and /.well-known/oauth-protected-resource discovery requests.
• This has been happening since at least February 23, 2026.

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What Should Happen?

The URL should be accepted and Claude should proceed with OAuth discovery and connection setup, allowing me to authenticate and use the Remote MCP Server.

Error Messages/Logs

No error messages or logs available. The claude.ai page immediately redirects to a full-page crash screen showing: 'Claude will return soon — Claude is currently experiencing a temporary service disruption. We're working on it, please check back soon.' No browser console errors are accessible as the page navigates away.

Steps to Reproduce

1. Go to https://claude.ai/settings/connectors
2. Click "Add" next to "Remote MCP Servers"
3. Paste any URL into the "Remote MCP Server URL" field (e.g. https://unclestock.com/mcp)
4. The page immediately crashes and shows "Claude will return soon"

No code or files needed — this is reproducible with any URL in the connector dialog.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

N/A - this bug is about claude.ai web app, not Claude Code CLI

Platform

Other

Operating System

Windows

Terminal/Shell

Other

Additional Information

Tested on Windows 11 with Chrome. The MCP server endpoints are functional — /.well-known/oauth-authorization-server and /.well-known/oauth-protected-resource both respond correctly (verified via curl). This issue has been occurring since at least February 23, 2026. Tried multiple different URLs with the same result.