Ephemeral messages

An ephemeral message appears only for one person, inline in the conversation, marked Only visible to you. It isn’t saved to the conversation: it disappears when the person reloads or dismisses it — the same behaviour as Slack.

Use them for confirmations (“Your refund was queued”), private hints, or a question only the person who clicked should answer.

Send one

POST /api/bot/chat.postEphemeral
Authorization: Bearer foxa-…

{
  "channel": "refunds",
  "user": "42bc76d7-…",
  "text": "Only you can see this",
  "blocks": [
    { "type": "section", "text": { "type": "mrkdwn", "text": "Refund *#4821* was queued. Want to undo it?" } },
    { "type": "actions", "elements": [{ "type": "button", "action_id": "undo", "style": "danger", "text": { "type": "plain_text", "text": "Undo" } }] }
  ]
}

Field	Description
`channel`	Channel id or short name. Required.
`user`	The person who sees it. They must be able to read the channel. Required.
`text`, `blocks`, `attachments`	As in chat.postMessage.
`thread_ts`	Show it in a thread.

The answer is { "ok": true, "message_ts": "…" }. REST API: POST /api/v1/chat/channels/{id}/ephemeral with userId, body, blocks, attachments, parentMessageId.

Controls in ephemeral messages

Buttons and menus work. Their block_actions payload has container.is_ephemeral: true and no message, and a response_url that can replace (replace_original) or delete (delete_original) the ephemeral message. Controls stay usable for 24 hours.

The response_url of any interaction also posts an ephemeral message when you send text or blocks without response_type — Slack’s default.