Custom MCP server in Codex Web

support codex codex-web codex-cloud mcp

We tested custom MCP registration in Codex Web by appending a Datadog MCP server to /opt/codex/config.toml during setup.

What we verified:

  • the MCP config is present on disk after setup;
  • required environment variables are present;
  • the Datadog MCP endpoint is reachable from the runtime;
  • however, no Datadog MCP tools are exposed in the active Codex Web session.

This suggests that modifying /opt/codex/config.toml during setup is not sufficient to register custom MCP servers in Codex Web, and that MCP tool availability is controlled by platform/session bootstrap rather than runtime config changes.

Can you confirm:

  • whether custom MCP servers are officially supported in Codex Web / Codex Cloud;
  • if supported, what the correct setup path is;
  • if not supported, whether this is a planned capability?