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A Slack conditional rule matches Slack activity by the channel it happens in. For example, you can remove messages from #finance when the Support group reads Slack, or stop agents from posting to externally shared channels. Setup has two steps:
  1. Connect the Slack (User) MCP server in Barndoor so it can list your workspace’s channels.
  2. Create the conditional rule in Field Controls.
This guide applies to the Barndoor-hosted Slack (User) MCP server from the MCP server directory. Conditional rules are not available for Slack Bot or other Slack servers.

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Prerequisites

You need:
  • Admin access to your Barndoor organization
  • A Slack user who can see the channels you want to govern

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1. Connect the Slack (User) MCP server

In this guide, service account means the organization-level OAuth connection on the Barndoor server detail page. Barndoor uses it to list your workspace’s channels when you build a rule.
  1. Navigate to Admin → MCP Servers.
  2. Add Slack (User) from the Barndoor-hosted MCP server directory, or open an existing Slack (User) server.
  3. On the server detail page, connect the service account with a Slack user who can see the channels you want to govern. The channel list includes the public and private channels that user can see, including archived channels.
If the service account isn’t connected when you create a rule, the When section prompts you to connect it. Click Connect service account, complete the Slack OAuth flow, and continue.

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2. Create the conditional rule

With the service account connected, you can build the rule.
  1. Navigate to Data Control Center → Field Controls.
  2. Click Add Conditional Rule.
  3. Enter a Name and select your Slack (User) server under Server. The rule applies to every tool on the server.
  4. Optionally, add groups or roles under Target Group / Role. Leave it empty to apply the rule to all users.
  5. Under When, choose a condition:
  6. Under Applies to, choose All tools, Read (tool results), or Write (create, update, and delete calls).
  7. Under Then, choose Filter to remove matching items from results, or Block to deny matching calls or results. Filter isn’t available for Write: writes are always blocked outright.
  8. Click Add Rule.
Add Conditional Rule dialog for Slack (User) with the #finance channel selected, applying to Read with the Filter action

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Choose channels

Search the list of channels from your workspace and select one or more. You can also type a channel name, or a wildcard pattern such as proj-* or *-prod, for channels that aren’t listed. When section with the listed channels #general and a saved channel, plus the typed name proj-* Pick from the list where you can. If you type the name of a channel that is listed, Barndoor uses the listed channel’s ID instead. Typed names are for channels the service account can’t see. Hover the info icon next to the condition description for a reminder: Choosing Slack channels hint explaining that listed channels are stored by ID and typed names or wildcards are stored as text A few entries aren’t accepted:
  • Pasted Slack IDs or channel links. Pick the channel from the list, or type its name.
  • A wildcard on its own, such as *. To cover every channel of a kind, use a Channel type rule instead.
Large workspaces can take a moment to load. Barndoor loads up to 2,000 channels. If the list isn’t complete, the When section says so. Search it, or type the name of a channel that isn’t shown.

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Choose channel types

Channel type matches every conversation of the kinds you select: Each conversation has exactly one type. When more than one applies, the first match in this order wins: Externally shared, then Direct message or Group DM, then Private channel, then Public channel. For example, a private channel shared with a partner organization is Externally shared, so a Private channel rule doesn’t match it. Select both types to cover it.

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What a rule matches

  • Read checks the channels, messages, and files that Slack tools return. Filter removes matching items and returns the rest. Block denies the whole result if any item matches.
  • Write checks where a message is posted. Before the message is sent, Barndoor looks up the target channel and blocks the post if it matches.
  • All tools applies both checks.

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Examples

Hide finance channels from the Support group:
  • When: Channel is #finance, #finance-ops
  • Applies to: Read
  • Then: Filter
  • Target Group / Role: customer-support
Stop agents from posting to externally shared channels:
  • When: Channel type is Externally shared
  • Applies to: Write
  • Then: Block
Keep project channels out of agent reads and writes:
  • When: Channel is proj-* (typed wildcard)
  • Applies to: All tools
  • Then: Block

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Troubleshooting

The list only shows channels the connected service account can see, up to 2,000 channels. Type the channel name instead, or reconnect the service account with a Slack user who is a member of that channel.
Barndoor doesn’t save channel IDs or links that you paste. Pick the channel from the list, or type its name.
The value you typed looks like a Slack channel ID. Type a lowercase channel name such as proj-*, or pick the channel from the list.
A wildcard on its own, such as * or #*, isn’t accepted. Create a rule with When set to Channel type and select the kinds of channel to cover.