Registering the Bareun MCP server in Codex CLI

If you connect the Bareun MCP server to OpenAI Codex CLI, Codex calls Bareun directly while it works to perform Korean morphological analysis and spell checking.

What you need

A Bareun API key: for issuing keys and usage, see Using the cloud.
The endpoint address: for Bareun cloud it is https://api.bareun.ai:443/mcp. If you installed the spell checker yourself, use /mcp on that server's address (for example, http://localhost:5656/mcp). MCP is offered only in Bareun builds that include the spell checker, and installations for morphological analysis only do not have /mcp.

How to register

Codex keeps its MCP settings in ~/.codex/config.toml (or .codex/config.toml of a trusted project). Add a [mcp_servers.<name>] table for each server, and specify url for a remote HTTP server. Choose one of the two authentication methods below.

Put the API key in an environment variable and point to it with bearer_token_env_var. This value is sent automatically as an Authorization: Bearer ... header.

[mcp_servers.bareun]
url = "https://api.bareun.ai:443/mcp"
bearer_token_env_var = "BAREUN_API_KEY"

Set the environment variable before running.

export BAREUN_API_KEY="YOUR_API_KEY"

You can also specify the api-key header directly with http_headers.

[mcp_servers.bareun]
url = "https://api.bareun.ai:443/mcp"
http_headers = { "api-key" = "YOUR_API_KEY" }

If you have an older Codex

If your Codex version does not support remote HTTP MCP (url), you can register the mcp-remote bridge as a command-based (stdio) server (Node.js required).

[mcp_servers.bareun]
command = "npx"
args = ["-y", "mcp-remote", "https://api.bareun.ai:443/mcp", "--header", "api-key: YOUR_API_KEY"]

Verifying the connection

Check the registered servers with codex mcp list in a terminal.
If you ask something like "Correct this sentence with Bareun" in a Codex session, it calls the Bareun tools (analyze_syntax, tokenize, list_pos_tags, correct_grammar).

Troubleshooting

Server not connecting? Check the table name in config.toml ([mcp_servers.bareun]) and the /mcp at the end of url. Also check that there are no TOML syntax errors.
Authorization error (401)? Check that the environment variable that bearer_token_env_var points to actually contains the key, or that the api-key value in http_headers is correct.
Is the project .codex/config.toml ignored? Project settings apply only in trusted projects. Check your trust settings or use the user settings (~/.codex/config.toml).

Frequently asked questions

Q. Should I use `bearer_token_env_var` or `http_headers`?

If you do not want to write the key directly in a config file, the environment variable token (bearer_token_env_var) is safer. Bareun accepts both the Authorization: Bearer <key> and api-key headers, so either works.

Q. My Codex version does not support remote HTTP MCP.

Register mcp-remote as a command-based (stdio) server. Set command = "npx" and put mcp-remote, the endpoint, and the header in args (Node.js required).