How to Connect Multiple Slack Workspaces to Codex
Two very different questions hide behind this one, and mixing them up wastes an afternoon. Codex has an official Slack integration, but it exists to launch coding tasks from a channel, not to read Slack as a data source. Which multi-workspace problem you have decides which half of this guide you need. Carly holds your Gmail and Outlook mailboxes and every calendar on both sides in the same place.
1. Add your Slack workspaces to Carly
- Sign in at carlyassistant.com.
- Open carlyassistant.com/integrations.
- Find Slack, click Connect, and authorize the workspace.
- Click Connect again for the next one, and keep going for as many workspaces as you want.
On a client workspace where you are not an admin, their Slack administrator approves the install.
Carly connects to thousands of apps, so while you are on that page you can add your inboxes, calendars, CRM, and anything else you want Codex to reach through the same connector.
2. Register Carly as an MCP server
codex mcp add carly --url https://carlyassistant.com/mcp/Servers added this way land in ~/.codex/config.toml at user scope. The manual entry is equivalent:
[mcp_servers.carly]
url = "https://carlyassistant.com/mcp/"Then authenticate:
codex mcp login carlyComplete the OAuth flow in the browser, signing in to the Carly workspace holding the Slack connections. Confirm the server is live:
codex mcp listThe two questions
Mention @Codex in a channel or thread and it reads the surrounding messages for context, kicks off a cloud coding task against your connected GitHub repo, and replies with a link to the result. Triage a bug in a channel, get a pull request, without leaving Slack.
Codex reaches non-development apps through the Model Context Protocol. You could register a Slack MCP server per workspace, and then you maintain three server entries, three OAuth apps, and no vocabulary in the prompt for saying which workspace you mean, so the agent uses whichever loaded first.
The official app versus Carly in Codex
| Need | Codex Slack app | Carly MCP server |
|---|---|---|
| Launch a coding task from a channel | Yes | No |
| Read channels as a data source | For task context only | Yes |
| Reach several workspaces | Install per workspace | One server, all workspaces |
| Route or follow up on messages | No | Yes |
| Act when a message arrives | No | Yes |
| Requires GitHub and an environment | Yes | No |
| Keep the work running outside Codex | No | Yes |
These are complements rather than competitors. Keep the Codex Slack app for what it is genuinely good at, which is turning a bug thread into a pull request. Use one MCP server for the Slack work that is not about code.
Free Zapier-style workflows; AI agents from $35/month. Connect it on the integrations page, or start with Slack.
Quick fixes
| Problem | Fix |
|---|---|
| Tools do not show up | Start a new Codex session after adding the server |
codex mcp login never completes | Finish the browser OAuth flow, then rerun codex mcp list |
@Codex does nothing in a channel | Confirm a connected GitHub account and a configured environment |
| The Slack app will not install | A Slack admin in that workspace approves it |
| Posts land in the wrong workspace | Name the workspace and require confirmation before writes |
Frequently asked questions
Can Codex connect to more than one Slack workspace?
For launching coding tasks, install the Codex Slack app in each workspace. For reading and acting across workspaces, use one MCP server that holds all of them, because the official app does not read Slack as a data source.
Does the Codex Slack app manage messages?
No. It exists to start cloud coding tasks against your GitHub repo from a channel. Triage, routing, and follow-up are outside what it does.
What does the Codex Slack app require?
A Plus, Pro, Business, Edu, or Enterprise plan, a connected GitHub account, at least one configured environment, and a Slack admin’s approval to install.
Should I use Codex for Slack operations work?
Codex is a coding agent, and its integrations assume repos and environments. Channel triage and follow-up belong in a workflow that runs without a session open.
Related: Codex + Slack · Multiple Slack workspaces in ChatGPT Work · Multiple Slack workspaces in Claude · Multiple Gmail accounts in Codex · What is MCP
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