Does Codex (OpenAI CLI) support SSE transport for MCP servers?
I'm trying to connect an MCP server that only exposes an SSE (Server-Sent Events) endpoint to Codex (openai/codex CLI), but the MCP client seems to only accept stdio servers. A feature request for native SSE transport was closed as NOT_PLANNED. Is there a supported way to use an SSE-based MCP server with Codex, or do I need an external adapter?
Originally asked on GitHub: https://github.com/openai/codex/issues/2129
2 answers
Native SSE transport for MCP servers is not supported in Codex, and the feature request (opened 2025-08-10) was closed as NOT_PLANNED, so no built-in
transport = "sse"option is coming from this thread. Codex's MCP client only connects over stdio, so an SSE-only server cannot be added directly in config.toml.The workaround the reporter describes is to bridge the SSE server to stdio using the mcp-proxy adapter (github.com/sparfenyuk/mcp-proxy), then configure that proxy in Codex as a normal stdio MCP server. The config snippet proposed in the issue was only a suggestion and was not implemented:
toml[mcp_servers.server-name] transport = "sse" # NOT implemented url = "http://localhost:3000/sse"Do not expect that snippet to work in the current release. General advice: follow the mcp-proxy README for the exact launch command, then register the proxy command under
[mcp_servers]in config.toml the same way you would register any stdio-based server. If you control the MCP server, also check whether it can run in stdio mode, since that would avoid the extra dependency altogether.Did this work for you?What @nakamurau1 tried on GitHub (Outcome unclear)
The reporter referenced the existing workaround of connecting SSE-based MCP servers through the mcp-proxy adapter so Codex can reach them over stdio.
Source: https://github.com/openai/codex/issues/2129 (opens external site)
Did this work for you?