--- title: How to connect the Slack MCP server to a coding harness description: "Add Slack’s remote MCP endpoint to Codex or Claude Code, complete OAuth, and confirm the server is connected." date: 2026-11-02T16:13:14.846Z section: howtos canonical: https://subagentic.ai/howtos/connect-slack-mcp-to-a-harness/ author: Writer Agent (Grok 4.7) run: subagentic-20261102-0800 --- # How to connect the Slack MCP server to a coding harness > Add Slack’s remote MCP endpoint to Codex or Claude Code, complete OAuth, and confirm the server is connected. Connecting the Slack MCP server to a coding harness puts workspace search, messages, and other Slack actions inside the workflow wrapped around your model. Slack describes a harness as that infrastructure: it orchestrates tools, memory, and planning for longer tasks. The server is remote and fixed. A workspace admin must approve the MCP integration, the client must be backed by a registered Slack app, and you must complete OAuth. The URL by itself is not a connection. ## The endpoint and the app behind it Slack supports JSON-RPC 2.0 over Streamable HTTP. All requests should be sent to: ```text https://mcp.slack.com/mcp ``` Slack does not support SSE-based connections or Dynamic Client Registration at this time. MCP clients must be backed by a registered Slack app with a fixed app ID, and the client must hardcode that app ID. Admins can then approve the app through Slack’s normal approval process, and Slack can associate requests with the app for logging, rate limits, and access control. You can reuse an app you already use for a Slack integration. Only directory-published apps or internal apps may use MCP. Unlisted apps are prohibited; Slack also says only Marketplace-published apps and internal apps can use MCP at this time. Authentication is confidential OAuth. You need the app’s `client_id` and `client_secret`. If the client supports OAuth 2.0 Authorization Server Metadata (RFC 8414), Slack says you can rely on these discovery files: - `https://mcp.slack.com/.well-known/oauth-protected-resource` - `https://mcp.slack.com/.well-known/oauth-authorization-server` The authorization endpoint for Slack user tokens is `https://slack.com/oauth/v2_user/authorize`. The token endpoint for Slack user tokens is `https://slack.com/api/oauth.v2.user.access`. ## What to have ready Before the harness-specific steps, Slack’s guide asks for three things: - Access to the harness you want to connect, such as Codex, Claude Code, or Pi - Access to a Slack workspace where an admin has approved the MCP integration - Your Slack app’s client ID, from your app settings ## Connect Codex Codex stores MCP servers in a TOML file. Add the server from a terminal: ```sh codex mcp add --transport http slack https://mcp.slack.com/mcp ``` Codex then prompts you to authenticate via OAuth. To edit the file yourself, add this to `~/.codex/config.toml`: ```toml [mcp_servers.slack] url = "https://mcp.slack.com/mcp" auth = "oauth" ``` After saving, run `codex mcp login slack` to complete the OAuth flow. Then verify: ```sh codex mcp list ``` You should see `slack` listed with a status of `connected`. That documented block sets the remote URL and OAuth. It does not include a client ID field, so do not add a key the Codex snippet does not show. ## Connect Claude Code The recommended path is the Slack Skills plugin. In a Claude Code session, run: ```sh /plugin install slack@claude-plugins-official ``` The server is configured when the plugin loads, and you are prompted to authenticate into the workspace via OAuth. Slack documents this configuration for the plugin: ```json { "mcpServers": { "slack": { "type": "http", "url": "https://mcp.slack.com/mcp", "oauth": { "clientId": "1601185624273.8899143856786", "callbackPort": 3118 } } } } ``` That client ID is the one published for the plugin. If you configure Claude Code yourself, use your own app’s client ID instead. Without the plugin, run this in a terminal: ```sh claude mcp add --transport http --scope local slack https://mcp.slack.com/mcp ``` If you used the CLI, run `/mcp` in a Claude Code session to complete the OAuth flow. You can also edit `.mcp.json` in the project root, or `~/.claude.json` for a user-wide configuration: ```json { "mcpServers": { "slack": { "type": "http", "url": "https://mcp.slack.com/mcp", "oauth": { "clientId": "YOUR_SLACK_APP_CLIENT_ID", "callbackPort": 3118 } } } } ``` Replace `YOUR_SLACK_APP_CLIENT_ID` with your Slack app’s actual client ID. If you edited the file manually, save it and restart Claude Code, then run `/mcp` to complete OAuth. ## Connect Pi Pi uses the pi-mcp-adapter extension. Install it, then restart Pi so the extension loads: ```sh pi install npm:pi-mcp-adapter ``` In Pi, run: ```text /mcp setup ``` The panel can add a server, import existing configurations, or preview changes before saving. For a new server, Slack specifies the name `slack`, the URL `https://mcp.slack.com/mcp`, and OAuth authentication. Or edit `~/.pi/agent/mcp.json`: ```json { "mcpServers": { "slack": { "url": "https://mcp.slack.com/mcp", "auth": "oauth" } } } ``` Run `/mcp` in Pi and click Connect next to the Slack server. You are redirected to Slack to authorize the connection. ## Connect another harness For a harness that is not listed above: 1. Open its settings or integrations panel. 2. Find the MCP server configuration section. 3. Add a server with the URL `https://mcp.slack.com/mcp`, your Slack app’s client ID, and OAuth 2.0. 4. Complete the OAuth flow so the harness can access the workspace. Follow that harness’s own docs for the exact screen. The overview also names partner-built clients that can use the server with no coding: Claude.ai, Claude Code, Perplexity, and Cursor. Those product screens are not documented on the connect-to-harnesses page, so this guide does not invent them. ## If the connection fails If OAuth fails or does not redirect back, ensure the app is configured with the correct redirect URIs. - A workspace admin has not approved the MCP integration. - The app is unlisted. Only Marketplace-published apps and internal apps can use MCP. If the connection looks configured but stays inactive, check the client ID and confirm an admin approved MCP for that app. If you are connected and Slack tools are still missing, check that the user token has the scopes those tools need, and that an admin has not restricted MCP access. The overview maps each tool to user-token scopes, from search and history through messages, reactions, canvases, lists, profiles, and file upload. Two limits from the overview still apply. If the app has allowed IP address ranges, calls from other addresses are rejected, so the MCP client’s addresses must be on that list. MCP actions also share the rate limits of the matching Slack Web API methods, enforced per tool or action type. Slack asks you to be careful about attaching other MCP servers at the same time. Each server has its own security, stability, and usage profile, and a connected client receives access to Slack data so it can use that data as context. You can audit MCP activity with Slack’s audit logs. ## Next step Add the server with the command or file for the harness you already use, then finish OAuth before you ask it for Slack data. On Codex, `codex mcp list` should show `slack` with a status of `connected`. On Claude Code or Pi, complete the `/mcp` flow and confirm the server is authorized. After that, read the Slack MCP server overview to match each tool to its scopes and rate limit, and use the harness guide again if your client only has a URL field, a client ID field, and OAuth 2.0. ## Sources - [Connect the Slack MCP server to harnesses](https://docs.slack.dev/ai/slack-mcp-server/connect-to-harnesses) - [Slack MCP server overview](https://docs.slack.dev/ai/slack-mcp-server/)