Slack

Triggers turn an agent into a long-lived service that waits for events, acts on them, delivers the result, and goes idle. The slack trigger connects that loop to a Slack workspace over Socket Mode — an outbound WebSocket, so the agent needs no public endpoint. It watches channels and replies in a thread under the messages that wake it.

triggers:
  - type: slack
    channels: ["help"]          # names or ids; omit for all channels the bot is in
    # require_mention: true     # only respond when @-mentioned (DMs always respond)
    # token_env: SLACK_BOT_TOKEN (default)
    # app_token_env: SLACK_APP_TOKEN (default)
    # from_users: ["U0HAPPY"]   # only handle these authors (Slack user ids)
    # reply_channel: "C0REVIEW" # post replies here instead of the source thread
    # allow_silence: true       # a reply of exactly __NO_REPLY__ posts nothing

Setup

Setting up the Slack app takes about 10 minutes:

1. In api.slack.com/apps, create a new app (from scratch) in your workspace.
2. Under Socket Mode, enable it and generate an app-level token with the connections:write scope — this is SLACK_APP_TOKEN (xapp-…).
3. Under OAuth & Permissions, add the bot scopes chat:write, channels:history, groups:history, im:history, and channels:read, then install the app to the workspace. The bot token it produces is SLACK_BOT_TOKEN (xoxb-…).
4. Under Event Subscriptions, enable events and subscribe to the bot events message.channels, message.groups, and message.im. Missing event subscriptions are the most common setup failure — the socket connects but nothing arrives.
5. Export both tokens, invite the bot to a channel (/invite @your-bot), and run the agent: af run agent.yaml

Replies go into a thread under the triggering message; conversations are keyed per thread (a DM is one rolling conversation), and memory.scope: thread continues them (Memory). The agent ignores bots, itself, message edits, and empty messages; long replies split at Slack's recommended 4000-char limit. If you change scopes later, reinstall the app — Slack applies them only on install.

Observer agents

Three optional keys together turn the trigger from a chatbot into an observer — an agent that watches channels, reacts to specific people, and reports elsewhere (a review bot, a moderation assistant, a coach):

• from_users — handle only these authors (Slack user ids, the U… kind). The filter runs before the model is called: everyone else's messages are dropped in the trigger and never reach the provider.
• reply_channel — deliver replies to a dedicated channel instead of the source thread. Out-of-channel replies quote the triggering message and link back to it.
• allow_silence — let the agent say nothing. Instruct it in purpose to answer with exactly __NO_REPLY__ when it has no feedback; the trigger then posts nothing instead of a "looks fine" reply on every message.

Every run — replied or silent — lands in the agent's run history with its status, steps and tokens.