Add McpMux as MCP client

[its-mash]

Summary

• Adds McpMux to the MCP clients list

McpMux is a free, open-source desktop app and local MCP gateway. Users configure MCP servers once and connect every AI client (Cursor, Claude Desktop, VS Code, Windsurf) through a single localhost:45818 endpoint. Credentials are encrypted in the OS keychain instead of plain-text JSON.

• Website: https://mcpmux.com
• GitHub: https://github.com/mcpmux/mcp-mux
• Capabilities: tools, resources, prompts
• Protocol version: 2025-06-18

[jirispilka]

Hi @its-mash — sorry for the long delay getting to this, and thanks for contributing McpMux here.

I ran this through a verification pass against the Contributors guide and McpMux's own source, and found two issues that need addressing before this can merge:

1. No evidence for the capability claims

The contributor guide asks for "a screenshot from usage, link to its source code, or official docs" backing the capability claims. This PR asserts tools, resources, prompts support without pointing at anything that confirms it.

2. The registry key doesn't match McpMux's actual MCP client identity

This registry's key is meant to equal the literal clientInfo.name string sent during the MCP initialize handshake. Looking at the mcpmux/mcp-mux source:

• The outbound client connection to a backend MCP server (crates/mcpmux-gateway/src/pool/instance.rs) builds its identity as format!("mcpmux-{}", server_id) (e.g. mcpmux-github, mcpmux-notion) — never the bare string "mcpmux".
• "mcpmux-gateway" does appear in the source, but that's McpMux's server identity — what it presents to Cursor/Claude Desktop/etc. — the opposite direction from what this registry tracks.

Since McpMux mints a distinct client name per backend server rather than a single fixed identity, it's not clear a single "mcpmux" entry can represent that correctly under this registry's one-key-per-client schema — worth clarifying what should actually key this entry.

Could you clarify what client identity should represent McpMux here, and add a source/docs link backing the declared capability set? Happy to take another look once that's addressed.

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