OpenAI Codex

OpenAI Codex supports MCP servers through two interfaces: the Codex CLI (terminal-based) and Codex Desktop (GUI application). Both support STDIO and Streamable HTTP transports.

Codex CLI

Config File Location

Basic Setup

Add a single server to ~/.codex/config.toml:

[mcp_servers.snomed]
command = "/usr/local/bin/snomed-mcp"

Complete Configuration

All seven servers:

[mcp_servers.snomed]
command = "/usr/local/bin/snomed-mcp"
env_vars = ["SNOWSTORM_BRANCH"]

[mcp_servers.rxnorm]
command = "/usr/local/bin/rxnorm-mcp"

[mcp_servers.icd10]
command = "/usr/local/bin/icd10-mcp"

[mcp_servers.ucum]
command = "/usr/local/bin/ucum-mcp"

# Servers requiring credentials (set env vars before starting Codex)
[mcp_servers.icd11]
command = "/usr/local/bin/icd11-mcp"
env_vars = ["ICD11_CLIENT_ID", "ICD11_CLIENT_SECRET"]

[mcp_servers.loinc]
command = "/usr/local/bin/loinc-mcp"
env_vars = ["LOINC_USERNAME", "LOINC_PASSWORD"]

[mcp_servers.umls]
command = "/usr/local/bin/umls-mcp"
env_vars = ["UMLS_API_KEY"]

CLI Registration

Instead of editing the config file, you can register servers via CLI:

# Servers without authentication
codex mcp add snomed /usr/local/bin/snomed-mcp
codex mcp add rxnorm /usr/local/bin/rxnorm-mcp
codex mcp add icd10 /usr/local/bin/icd10-mcp
codex mcp add ucum /usr/local/bin/ucum-mcp

# Servers requiring credentials
codex mcp add icd11 --env ICD11_CLIENT_ID=$ICD11_CLIENT_ID --env ICD11_CLIENT_SECRET=$ICD11_CLIENT_SECRET -- /usr/local/bin/icd11-mcp
codex mcp add loinc --env LOINC_USERNAME=$LOINC_USERNAME --env LOINC_PASSWORD=$LOINC_PASSWORD -- /usr/local/bin/loinc-mcp
codex mcp add umls --env UMLS_API_KEY=$UMLS_API_KEY -- /usr/local/bin/umls-mcp

Remote / HTTP Setup (CLI)

Connect to a remote server running in HTTP mode:

[mcp_servers.snomed]
url = "https://your-server.com/snomed/mcp"
bearer_token_env_var = "MCP_API_KEY"

Codex Desktop

Codex Desktop provides a graphical interface for managing MCP servers. You can configure servers in both STDIO and Streamable HTTP modes through the settings panel.

Adding a Server (STDIO)

In Codex Desktop, navigate to Settings > MCP Servers and add a new server with these fields:

• Server Name: snomed (or any identifier)
• Command: /usr/local/bin/snomed-mcp
• Arguments: (leave empty)
• Environment Variables: Add key-value pairs as needed (e.g., SNOWSTORM_BRANCH = MAIN/SNOMEDCT-US)
• Working Directory: (optional)

For servers requiring credentials, add the credential environment variables in the Environment Variables section:

Adding a Server (Streamable HTTP)

For remote servers, select the HTTP transport type and configure:

• Server Name: snomed
• URL: https://your-server.com/snomed/mcp
• Bearer Token: (optional, for authenticated endpoints)
• Custom Headers: (optional)

Servers Requiring Credentials

Three servers need credentials configured via environment variables or system keyring:

Start with servers that don’t require authentication (snomed, rxnorm, icd10, ucum) and add authenticated services as needed.

See HTTP Transport for server-side setup and Remote Deployment for deployment guides.