Slack MCP Setup (macOS Keychain)

This workstation uses macOS Keychain to store Slack MCP tokens securely. Tokens are fetched at darwin-rebuild switch time and injected into OpenCode config.

Architecture

• Slack MCP is injected into opencode.json with tokens from Keychain
• MCP is disabled by default ("enabled": false) to keep slack tools out of normal sessions
• To use Slack: manually enable the MCP, or delegate to the slack agent

Why disabled by default?

• Prevents accidental Slack API calls from main agents
• Reduces MCP server startup overhead when not needed
• Slack tools only available when explicitly enabled

Initial Setup

1. Get Tokens from Slack

Open Slack in a web browser (https://app.slack.com or Okta tile). Must be in web client (URL like app.slack.com/client/T.../...).

Get XOXC Token

1. Open DevTools (Cmd+Option+I or F12)
2. Go to Console tab
3. Type allow pasting and press Enter
4. Run:

JSON.parse(localStorage.localConfig_v2).teams[document.location.pathname.match(/^\/client\/([A-Z0-9]+)/)[1]].token

5. Copy the xoxc-... token

Get XOXD Token

1. In DevTools, go to Application tab (Chrome) or Storage tab (Firefox)
2. Expand Cookies → click Slack domain
3. Find cookie named d (single letter)
4. Double-click its Value, copy the xoxd-... value

Firefox users: Decode URL-encoded characters:

• %2F → /
• %2B → +

2. Store Tokens in Keychain

# Add XOXC token
security add-generic-password -a "$USER" -s slack-mcp-xoxc-token -w "xoxc-YOUR-TOKEN-HERE" -U

# Add XOXD token
security add-generic-password -a "$USER" -s slack-mcp-xoxd-token -w "xoxd-YOUR-TOKEN-HERE" -U

The -U flag updates if the item already exists.

3. Apply Configuration

darwin-rebuild switch --flake .#$(hostname -s)

The activation script will:

• Fetch tokens from Keychain
• Inject Slack MCP config into ~/.config/opencode/opencode.json
• If tokens missing: delete any existing Slack config and warn

4. Verify

# Check config was created
jq '.mcp.slack' ~/.config/opencode/opencode.json

# Should show:
# {
#   "type": "local",
#   "command": ["npx", "-y", "slack-mcp-server@latest", "--transport", "stdio"],
#   "enabled": false,
#   "environment": {
#     "SLACK_MCP_XOXC_TOKEN": "xoxc-...",
#     "SLACK_MCP_XOXD_TOKEN": "xoxd-...",
#     ...
#   }
# }

# Verify opencode boots without errors
opencode --version

5. Restart OpenCode

Restart OpenCode to load the new MCP server. First use triggers cache build (takes several minutes for large workspaces).

Token Refresh

When you see invalid_auth errors, tokens have expired. Refresh them:

1. Get new tokens from Slack (see "Get Tokens from Slack" above)
2. Update Keychain:

security add-generic-password -a "$USER" -s slack-mcp-xoxc-token -w "NEW-XOXC-TOKEN" -U
security add-generic-password -a "$USER" -s slack-mcp-xoxd-token -w "NEW-XOXD-TOKEN" -U

3. Re-run: darwin-rebuild switch --flake .#$(hostname -s)
4. Restart OpenCode

Troubleshooting

Cache Files

Slack MCP creates cache files in working directory:

~/Library/Caches/slack-mcp-server/users_cache.json
~/Library/Caches/slack-mcp-server/channels_cache_v2.json

Gitignore recommendation: Add .*.json to .gitignore in repos where you use Slack MCP to avoid committing cache files.

Using Slack

Option 1: Enable MCP temporarily

# Enable the MCP
jq '.mcp.slack.enabled = true' ~/.config/opencode/opencode.json > /tmp/oc.json && mv /tmp/oc.json ~/.config/opencode/opencode.json

# Restart OpenCode, use slack tools directly

# Disable when done
jq '.mcp.slack.enabled = false' ~/.config/opencode/opencode.json > /tmp/oc.json && mv /tmp/oc.json ~/.config/opencode/opencode.json

Option 2: Delegate to slack agent

delegate_task(
  subagent_type="slack",
  load_skills=[],
  run_in_background=true,
  description="Search Slack for X",
  prompt="Find messages about [topic] in [channel/timeframe]. Return key findings with quotes and attribution."
)

Note: The slack agent still requires the MCP to be enabled.

Available tools for slack agent:

• slack_channels_list - List channels
• slack_conversations_history - Get channel messages
• slack_conversations_replies - Get thread replies
• slack_conversations_search_messages - Search messages with filters
• slack_conversations_add_message - Post messages (use carefully)

References

• Repo: https://github.com/korotovsky/slack-mcp-server
• Auth docs: https://github.com/korotovsky/slack-mcp-server/blob/master/docs/01-authentication-setup.md
• Activation script: users/dev/opencode-config.nix (home.activation.injectSlackMcpSecrets)
• Slack agent definition: assets/opencode/agents/slack.md (deployed to ~/.config/opencode/agents/)
• OpenCode agent docs: https://opencode.ai/docs (native markdown agent format)