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The Slack integration is in progress and not yet available for use. This page describes the planned integration. We’ll update it when Slack support ships.
Fabro’s Slack integration lets your team answer human-in-the-loop questions without leaving Slack. When a workflow reaches a human gate, Fabro posts an interactive message to a Slack channel with buttons for each option. Team members click a button (or reply in a thread for freeform input), and the workflow continues. The integration uses Slack’s Socket Mode, so no public URL or webhook endpoint is required — Fabro connects outbound over a WebSocket.

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What it looks like

When a workflow hits a human gate like this: 
approve [shape=hexagon, label="Approve Plan"]

approve -> implement [label="[A] Approve"]
approve -> plan      [label="[R] Revise"]
Fabro posts a message to your configured Slack channel:
Approve Plan [Approve] [Revise]
A team member clicks a button, the message updates to show the selection, and the workflow resumes on the chosen path.

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Supported question types

Question typeSlack UI
Yes/NoTwo buttons: Yes, No
ConfirmationTwo buttons: Yes, No
Multiple choiceOne button per option
Multi-selectCheckboxes with a Submit button
FreeformPrompt to reply in a thread
For freeform questions, Fabro posts a message asking the user to reply in the thread. The reply text (with any @mention prefix stripped) becomes the answer.

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Setup

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1. Create a Slack App

  1. Go to api.slack.com/apps and click Create New App
  2. Choose From scratch, give it a name (e.g. “Fabro”), and select your workspace

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2. Enable Socket Mode

  1. In the app settings sidebar, go to Socket Mode
  2. Toggle Enable Socket Mode on
  3. Create an App-Level Token with the connections:write scope
  4. Copy the token (starts with xapp-) — this is your FABRO_SLACK_APP_TOKEN

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3. Add bot token scopes

  1. Go to OAuth & Permissions in the sidebar
  2. Under Bot Token Scopes, add:
    • chat:write — post messages to channels
    • chat:write.public — post to channels without joining them

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4. Subscribe to events

  1. Go to Event Subscriptions in the sidebar
  2. Toggle Enable Events on
  3. Under Subscribe to bot events, add:
    • message.channels — receive channel messages (needed for freeform thread replies)

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5. Install the app

  1. Go to Install App in the sidebar
  2. Click Install to Workspace and authorize
  3. Copy the Bot User OAuth Token (starts with xoxb-) — this is your FABRO_SLACK_BOT_TOKEN

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6. Configure Fabro

Add both tokens to your .env file: 
FABRO_SLACK_BOT_TOKEN=xoxb-your-bot-token
FABRO_SLACK_APP_TOKEN=xapp-your-app-token
Optionally, set a default channel in your server configuration:
server.toml
[slack]
default_channel = "#fabro-reviews"

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7. Invite the bot

Invite the bot to any channel where you want it to post questions: 
/invite @Fabro
Or use the chat:write.public scope to post to public channels without an invite.

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How it works

Fabro uses the same web interviewer that powers the web UI. When a human gate fires:
  1. Fabro builds a Block Kit message from the question (buttons for choices, a thread prompt for freeform)
  2. Posts the message to the configured Slack channel
  3. The workflow blocks, waiting for an answer
When a user interacts:
  • Button click — Slack delivers the interaction over the Socket Mode WebSocket. Fabro maps the button’s action ID back to the question and submits the answer. The original message is updated to show the selection.
  • Thread reply (freeform) — The user replies in the message thread. Fabro receives the reply as a message event, matches it to the pending question via the thread timestamp, and submits the text as the answer.
The connection is maintained with automatic reconnection and exponential backoff (1s initial, 30s max). If the WebSocket disconnects, Fabro reconnects transparently — no manual intervention needed.

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Environment variables

VariableRequiredDescription
FABRO_SLACK_BOT_TOKENYesBot User OAuth Token (xoxb-...). Used to post and update messages.
FABRO_SLACK_APP_TOKENYesApp-Level Token (xapp-...). Used to connect via Socket Mode.
Both must be set for the Slack integration to activate. If either is missing or empty, Slack is disabled silently.

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Limitations

  • Interviews only — The Slack integration handles human gate questions. It does not post run status notifications or support steering running agents.
  • Single workspace — Fabro connects to one Slack workspace at a time.
  • One answer per question — The first person to click a button or reply in a thread provides the answer. Subsequent interactions on the same question are ignored.