Codex is one of the most popular coding harnesses out there. And MCP makes the experience even better. With Plain MCP integration, you can draft, triage, summarise emails, and much more, all without leaving the terminal or the app, whichever you prefer.
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Connect Plain without Auth hassles
We manage OAuth, API Key, token refresh, and scopes, you just build.
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Why use Composio?
Apart from a managed and hosted MCP server, you will get:
- CodeAct: A dedicated workbench that allows GPT to write its code to handle complex tool chaining. Reduces to-and-fro with LLMs for frequent tool calling.
- Large tool responses: Handle them to minimise context rot.
- Dynamic just-in-time access to 20,000 tools across 870+ other Apps for cross-app workflows. It loads the tools you need, so GPTs aren't overwhelmed by tools you don't need.
How to install Plain MCP in Codex
Run the setup command
Run this command in your terminal to add the Composio MCP server to Codex.
It will initiate the authentication in a browser window, authorize Codex to access your Composio account.
(Optional) Authenticate with OAuth
To authenticate manually, run the login command to open a browser window and authorize Codex to access your Composio account.
Verify the connection
Run codex mcp list to confirm Composio appears as a registered MCP server.
Codex App
Codex App follows the same approach as VS Code.
- Click ⚙️ on the bottom left → MCP Servers → + Add servers → Streamable HTTP:
- Fill the header and Key fields with
{ "x-consumer-api-key" = "ck_*******" }. - The Key is the Composio API key, that you can find on connect.composio.dev
- Click on Authenticate and authorize Codex to your Composio account and you're all set.
- Restart and verify if it's there in
.codex/config.toml
What is the Plain MCP server, and what's possible with it?
The Plain MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Plain account. It provides structured and secure access to your B2B support workspace, so your agent can perform actions like managing customers, creating support threads, fetching company details, handling issues, and organizing customer groups on your behalf.
- Customer management and onboarding: Automatically create new customer records, fetch customer information by email or ID, and add customers to specific support groups for better organization.
- Support thread creation: Let your agent create new support threads tied to customers, making it easy to kick off or escalate conversations without manual intervention.
- Issue tracking and retrieval: Fetch all external issue links associated with a customer, helping your team stay on top of ongoing problems and resolutions.
- Company and tier information access: Retrieve detailed company profiles and tier metadata, including contract value, owner details, and more, to personalize support interactions.
- User and customer cleanup: Safely delete customers or users from the system when offboarding or data hygiene is needed, all through agent-driven actions.
Supported Tools & Triggers
Tools
Conclusion
You've successfully integrated Plain with Codex using Composio's MCP server. Now you can interact with Plain directly from your terminal, VS Code, or the Codex App using natural language commands.
Key benefits of this setup:
- Seamless integration across CLI, VS Code, and standalone app
- Natural language commands for Plain operations
- Managed authentication through Composio
- Access to 20,000+ tools across 870+ apps for cross-app workflows
- CodeAct workbench for complex tool chaining
Next steps:
- Try asking Codex to perform various Plain operations
- Explore cross-app workflows by connecting more toolkits
- Build automation scripts that leverage Codex's AI capabilities
How to build Plain MCP Agent with another framework
Explore Other Toolkits
FAQ
What are the differences in Tool Router MCP and Plain MCP?
With a standalone Plain MCP server, the agents and LLMs can only access a fixed set of Plain tools tied to that server. However, with the Composio Tool Router, agents can dynamically load tools from Plain and many other apps based on the task at hand, all through a single MCP endpoint.
Can I use Tool Router MCP with Codex?
Yes, you can. Codex fully supports MCP integration. You get structured tool calling, message history handling, and model orchestration while Tool Router takes care of discovering and serving the right Plain tools.
Can I manage the permissions and scopes for Plain while using Tool Router?
Yes, absolutely. You can configure which Plain scopes and actions are allowed when connecting your account to Composio. You can also bring your own OAuth credentials or API configuration so you keep full control over what the agent can do.
How safe is my data with Composio Tool Router?
All sensitive data such as tokens, keys, and configuration is fully encrypted at rest and in transit. Composio is SOC 2 Type 2 compliant and follows strict security practices so your Plain data and credentials are handled as safely as possible.
