The agent can add and remove emoji reactions on messages using the message tool with the react action. Reaction behavior varies by channel and transport.

How it works

{
  "action": "react",
  "messageId": "msg-123",
  "emoji": "thumbsup"
}

• emoji is required when adding a reaction.
• Set emoji to an empty string ("") to remove the bot's reaction(s).
• Set remove: true to remove a specific emoji (requires non-empty emoji).
• On channels that support status reactions, trackToolCalls: true on a reaction lets the runtime use that reacted message for subsequent tool progress reactions during the same turn.

Channel behavior

Discord and Slack

- Empty `emoji` removes all of the bot's reactions on the message.
- `remove: true` removes just the specified emoji.

Google Chat

- Empty `emoji` removes the app's reactions on the message.
- `remove: true` removes just the specified emoji.

Nextcloud Talk

- Adding reactions only: `emoji` is required and must be non-empty.
- Reaction removal is not supported yet; calls with `remove: true` (or empty `emoji`) are rejected with a clear error rather than silently no-oping.
- Requires the Talk bot to be registered with the `reaction` feature (see [Nextcloud Talk channel docs](/en/channels/nextcloud-talk)).

Telegram

- Empty `emoji` removes the bot's reactions.
- `remove: true` also removes reactions but still requires a non-empty `emoji` for tool validation.

WhatsApp

- Empty `emoji` removes the bot reaction.
- `remove: true` maps to empty emoji internally (still requires `emoji` in the tool call).
- WhatsApp has one bot reaction slot per message; status reaction updates replace that slot rather than stacking multiple emoji.

Zalo Personal (zalouser)

- Requires non-empty `emoji`.
- `remove: true` removes that specific emoji reaction.

Feishu/Lark

- Use the `feishu_reaction` tool with actions `add`, `remove`, and `list`.
- Add/remove requires `emoji_type`; remove also requires `reaction_id`.

Signal

- Inbound reaction notifications are controlled by `channels.signal.reactionNotifications`: `"off"` disables them, `"own"` (default) emits events when users react to bot messages, and `"all"` emits events for all reactions.

iMessage

- Outbound reactions are iMessage tapbacks (`love`, `like`, `dislike`, `laugh`, `emphasize`, and `question`).
- Inbound tapback notifications are controlled by `channels.imessage.reactionNotifications`: `"off"` disables them, `"own"` (default) emits events when users react to bot-authored messages, and `"all"` emits events for all tapbacks from authorized senders.

Reaction level

Per-channel reactionLevel config controls how broadly the agent uses reactions. Values are typically off, ack, minimal, or extensive.

• Telegram reactionLevel — channels.telegram.reactionLevel
• WhatsApp reactionLevel — channels.whatsapp.reactionLevel

Set reactionLevel on individual channels to tune how actively the agent reacts to messages on each platform.

Related

• Agent Send — the message tool that includes react
• Channels — channel-specific configuration