Other clients

Any client that supports remote MCP servers over Streamable HTTP can use OnlyX. You need two things:


Server URL	`https://mcp.onlyx.ai/mcp`
Authentication	OAuth (the client discovers OnlyX’s sign-in automatically), or the header `Authorization: Bearer onx_sk_...` with an API key from Settings → API & MCP

Clients that support OAuth register themselves with OnlyX automatically; you never need a client ID or secret.

Windsurf

Windsurf’s Cascade agent reads MCP servers from mcp_config.json: ~/.codeium/windsurf/mcp_config.json in classic Windsurf, or ~/.config/devin/mcp_config.json (%APPDATA%\devin\mcp_config.json on Windows) in newer Devin Desktop builds. Open it from Cascade’s MCP settings and add:

OAuth
API key

mcp_config.json

{
  "mcpServers": {
    "onlyx": {
      "serverUrl": "https://mcp.onlyx.ai/mcp"
    }
  }
}

mcp_config.json

{
  "mcpServers": {
    "onlyx": {
      "serverUrl": "https://mcp.onlyx.ai/mcp",
      "headers": {
        "Authorization": "Bearer ${env:ONLYX_API_KEY}"
      }
    }
  }
}

Refresh the MCP servers in Cascade. With OAuth, Windsurf opens OnlyX’s sign-in the first time.

Gemini CLI

OAuth
API key

gemini mcp add --transport http --scope user onlyx https://mcp.onlyx.ai/mcp

Then, inside Gemini CLI, sign in:

/mcp auth onlyx

gemini mcp add --transport http --scope user \
  --header "Authorization: Bearer $ONLYX_API_KEY" onlyx https://mcp.onlyx.ai/mcp

Without --scope user, the server is added to the current project only (.gemini/settings.json). In a settings file, use httpUrl (not url) for OnlyX:

~/.gemini/settings.json

{
  "mcpServers": {
    "onlyx": {
      "httpUrl": "https://mcp.onlyx.ai/mcp",
      "timeout": 60000
    }
  }
}

OpenAI Codex CLI

OAuth
API key

codex mcp add onlyx --url https://mcp.onlyx.ai/mcp
codex mcp login onlyx

~/.codex/config.toml

[mcp_servers.onlyx]
url = "https://mcp.onlyx.ai/mcp"
bearer_token_env_var = "ONLYX_API_KEY"

Codex sends Authorization: Bearer <value of ONLYX_API_KEY>. Set the variable before starting Codex.

In the Codex interface, /mcp lists connected servers.

Any other client

Most clients accept a JSON block like this. Adjust the key names to your client (url, serverUrl or httpUrl; mcpServers or servers):

{
  "mcpServers": {
    "onlyx": {
      "type": "http",
      "url": "https://mcp.onlyx.ai/mcp",
      "headers": {
        "Authorization": "Bearer onx_sk_..."
      }
    }
  }
}

Leave out headers if your client supports OAuth for remote servers. If your client only supports local (stdio) servers, it cannot connect to OnlyX directly yet.

Test the server yourself

When a client will not connect, check the server and your key directly. This sends an MCP initialize request:

curl -i https://mcp.onlyx.ai/mcp \
  -H "Authorization: Bearer $ONLYX_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"curl-test","version":"1.0"}}}'

200 with a result naming the OnlyX server: the server and your key work; the problem is in the client’s configuration.
401: the credential was not accepted. Check the key, or sign in again. OnlyX’s 401 carries a WWW-Authenticate header pointing to its sign-in metadata, which is how OAuth clients find the login page.
403: the request came from a browser page OnlyX does not recognize. Connect from the client itself.

To browse the tools interactively, run the MCP Inspector with npx @modelcontextprotocol/inspector, choose Streamable HTTP, enter https://mcp.onlyx.ai/mcp, and either sign in with OAuth or add your key as a Bearer token.

Using OnlyX with Claude and other assistants: recipes that work in any client.
Tools: every tool.

MCP server

Connect your assistant

Reference

Windsurf

Gemini CLI

OpenAI Codex CLI

Any other client

Test the server yourself

Next

​Windsurf

​Gemini CLI

​OpenAI Codex CLI

​Any other client

​Test the server yourself

​Next

Windsurf

Gemini CLI

OpenAI Codex CLI

Any other client

Test the server yourself

Next