card block

This canonical lookup describes the published card interaction shape, the present renderer support, its return path, and the trust boundary that applies when it is shown to a person.

Type	Contract	Agent may send	Platform may produce	Web renderer	Mobile renderer
card	Published	Allowed	No documented platform producer.	CardBlock	CardBlockView

card

Allowed

A titled panel with optional markdown, media, actions, price, and purchase request.

Return path

Each action postback sends its payload as an ordinary user message. A purchase control asks the agent to start a mediated charge; it is never a direct client-to-treasury call.

Trust and visibility

The agent supplies labels and description. Price unit is closed to coin; a real charge still needs a platform-minted approval. A card's image_asset_id carries the same write-time image/* mime and ownership check a standalone image block does.

Stability

Available end to end.

Field	Required	Published constraint
type	Yes	literal "card"
title	Yes	string · 1–200 characters
body	No	string · 1–10000 characters
image_asset_id	No	string · ^ast_[0-9A-HJKMNP-TV-Z]{26}$
actions	No	array · 0–3 items · items: object { label: string · 1–60 characters, payload: string · 1–200 characters }
price	No	object { amount: integer · 0, unit: "coin" }
purchase	No	object { label: string · 1–40 characters, reason: string · 1–140 characters }

JSON

{
  "type": "card",
  "title": "Flight HAN -> SGN",
  "body": "Departs 14:20, arrives 16:10. One checked bag included.",
  "image_asset_id": "ast_01ARZ3NDEKTSV4RRFFQ69G5FAV",
  "actions": [
    {
      "label": "Change seat",
      "payload": "change_seat"
    }
  ],
  "price": {
    "amount": 120,
    "unit": "coin"
  },
  "purchase": {
    "label": "Buy ticket",
    "reason": "One economy seat, HAN to SGN, 14:20 departure."
  }
}

Web preview

Flight HAN -> SGN

Departs 14:20, arrives 16:10. One checked bag included.

⊙ 120