Add describer metadata property.

packages/manifest/bbm.schema.json

@@ -170,6 +170,10 @@
 					"$ref": "#/definitions/InputValues",
 					"description": "Arguments that are passed to the graph, useful to bind values to graphs."
 				},
+				"describer": {
+					"description": "The URL of the graph that will act as the describer for this graph. Can be a relative URL and refer to a sub-graph within this graph.\n\nThe describers in the format of \"module:name\" will be interpreted as \"use the `describe` export of the module named `name` to describe this graph\".",
+					"type": "string"
+				},
 				"description": {
 					"description": "The description of the graph.",
 					"type": "string"

packages/schema/breadboard.schema.json

@@ -86,6 +86,10 @@
 					"type": "string",
 					"description": "Version of the graph. [semver](https://semver.org/) format is encouraged."
 				},
+				"describer": {
+					"type": "string",
+					"description": "The URL of the graph that will act as the describer for this graph. Can be a relative URL and refer to a sub-graph within this graph.\n\nThe describers in the format of \"module:name\" will be interpreted as \"use the `describe` export of the module named `name` to describe this graph\"."
+				},
 				"metadata": {
 					"$ref": "#/definitions/GraphMetadata",
 					"description": "Metadata associated with the graph."

packages/types/src/graph-descriptor.ts

@@ -231,6 +231,16 @@ export type GraphInlineMetadata = {
    * [semver](https://semver.org/) format is encouraged.
    */
   version?: string;
+  /**
+   * The URL of the graph that will act as the describer for
+   * this graph. Can be a relative URL and refer to a sub-graph
+   * within this graph.
+   *
+   * The describers in the format of "module:name" will be interpreted as
+   * "use the `describe` export of the module named `name` to describe this
+   * graph".
+   */
+  describer?: string;
 };
 
 /**