server_to_client.json

{
  "title": "A2UI Message Schema",
  "description": "Describes a JSON payload for an A2UI (Agent to UI) message, which is used to dynamically construct and update user interfaces. A message MUST contain exactly ONE of the action properties: 'beginRendering', 'surfaceUpdate', 'dataModelUpdate', or 'deleteSurface'.",
  "type": "object",
  "additionalProperties": false,
  "properties": {
    "beginRendering": {
      "type": "object",
      "description": "Signals the client to begin rendering a surface with a root component and specific styles.",
      "additionalProperties": false,
      "properties": {
        "surfaceId": {
          "type": "string",
          "description": "The unique identifier for the UI surface to be rendered."
        },
        "catalogId": {
          "type": "string",
          "description": "The identifier of the component catalog to use for this surface. If omitted, the client MUST default to the standard catalog for this A2UI version (a2ui.org:standard_catalog_0_8_0)."
        },
        "root": {
          "type": "string",
          "description": "The ID of the root component to render."
        },
        "styles": {
          "type": "object",
          "description": "Styling information for the UI.",
           "additionalProperties": true
        }
      },
      "required": ["root", "surfaceId"]
    },
    "surfaceUpdate": {
      "type": "object",
      "description": "Updates a surface with a new set of components.",
      "additionalProperties": false,
      "properties": {
        "surfaceId": {
          "type": "string",
          "description": "The unique identifier for the UI surface to be updated. If you are adding a new surface this *must* be a new, unique identified that has never been used for any existing surfaces shown."
        },
        "components": {
          "type": "array",
          "description": "A list containing all UI components for the surface.",
          "minItems": 1,
          "items": {
            "type": "object",
            "description": "Represents a *single* component in a UI widget tree. This component could be one of many supported types.",
            "additionalProperties": false,
            "properties": {
              "id": {
                "type": "string",
                "description": "The unique identifier for this component."
              },
              "weight": {
                "type": "number",
                "description": "The relative weight of this component within a Row or Column. This corresponds to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
              },
              "component": {
                "type": "object",
                "description": "A wrapper object that MUST contain exactly one key, which is the name of the component type. The value is an object containing the properties for that specific component.",
                "additionalProperties": true
              }
            },
            "required": ["id", "component"]
          }
        }
      },
      "required": ["surfaceId", "components"]
    },
    "dataModelUpdate": {
      "type": "object",
      "description": "Updates the data model for a surface.",
      "additionalProperties": false,
      "properties": {
        "surfaceId": {
          "type": "string",
          "description": "The unique identifier for the UI surface this data model update applies to."
        },
        "path": {
          "type": "string",
          "description": "An optional path to a location within the data model (e.g., '/user/name'). If omitted, or set to '/', the entire data model will be replaced."
        },
        "contents": {
          "type": "array",
          "description": "An array of data entries. Each entry must contain a 'key' and exactly one corresponding typed 'value*' property.",
          "items": {
            "type": "object",
            "description": "A single data entry. Exactly one 'value*' property should be provided alongside the key.",
            "additionalProperties": false,
            "properties": {
              "key": {
                "type": "string",
                "description": "The key for this data entry."
              },
              "valueString": {
                "type": "string"
              },
              "valueNumber": {
                "type": "number"
              },
              "valueBoolean": {
                "type": "boolean"
              },
              "valueMap": {
                "description": "Represents a map as an adjacency list.",
                "type": "array",
                "items": {
                  "type": "object",
                  "description": "One entry in the map. Exactly one 'value*' property should be provided alongside the key.",
                  "additionalProperties": false,
                  "properties": {
                    "key": {
                      "type": "string"
                    },
                    "valueString": {
                      "type": "string"
                    },
                    "valueNumber": {
                      "type": "number"
                    },
                    "valueBoolean": {
                      "type": "boolean"
                    }
                  },
                  "required": ["key"]
                }
              }
            },
            "required": ["key"]
          }
        }
      },
      "required": ["contents", "surfaceId"]
    },
    "deleteSurface": {
      "type": "object",
      "description": "Signals the client to delete the surface identified by 'surfaceId'.",
      "additionalProperties": false,
      "properties": {
        "surfaceId": {
          "type": "string",
          "description": "The unique identifier for the UI surface to be deleted."
        }
      },
      "required": ["surfaceId"]
    }
  }
}