Most people assume Slack solves cross-team communication. And within a single workspace, it does. But once you have two separate Slack workspaces — an agency and a client, a parent company and a subsidiary, two long-term partners — you hit the same wall everyone else does.

Slack Connect helps, but it has limits. It requires both sides to be on paid plans, an admin on each side to approve the connection, and it only works with channels on the free tier. For ongoing, high-trust relationships where both sides already live in Slack, there's a simpler option.

TetherChat bridges two Slack workspaces natively. Messages flow both ways in real time, with full attribution — no bots posting on behalf of users, no webhook relays, no "messages from integration" noise. Both sides keep their normal Slack experience.

When this makes sense

Agency and client relationships where the client has their own Slack workspace. Asking them to join your workspace creates permission headaches. Asking everyone to use email defeats the purpose. A bridge puts both teams in the same conversation without either side giving up control of their workspace.

Subsidiaries and acquisitions where two companies that merged or partnered still run separate Slack instances. Before full consolidation happens — if it ever does — a bridge keeps teams working together without forcing a migration.

Long-term vendor relationships where both sides are already in Slack and want a dedicated channel that stays live for the duration of the relationship, with context going back months or years.

Setting it up

Step 1. Add TetherChat to your Slack workspace. A workspace admin approves the app — once installed, it's available in every channel.

Step 2. In the channel you want to connect, type /tether and choose "Create New Tether." TetherChat generates a unique Tether ID. Copy it.

Step 3. Repeat the installation in the other Slack workspace.

Step 4. In the corresponding channel in the second workspace, type /tether and choose "Connect to existing." Paste the Tether ID from step 2.

Messages posted in either channel now appear in both, in real time, with the sender's name and avatar intact.

What gets synced

Text messages, including formatting (bold, code blocks, bullet lists), file attachments and images, sender name and avatar, and thread replies within a bridged thread.

Each Tether connects one channel to one other channel. If you need to connect multiple channels, create a separate Tether for each.

Both workspaces need TetherChat installed. If one side removes the app, the connection pauses until it's reinstalled.

This is not Slack Connect. Slack Connect is Slack's built-in federation feature. TetherChat works differently — it bridges channels across platforms (including cross-platform connections like Slack to Teams or Discord), and also handles same-platform workspace-to-workspace connections like this one.

TetherChat is free during beta — no credit card required, unlimited channels. If you have two Slack workspaces that need to stay in sync, you can set up the first bridge in under five minutes.