Add an optional 'size' field to the Resource type.

docs/specification/draft/server/resources.md

@@ -246,6 +246,7 @@ A resource definition includes:
 - `name`: Human-readable name
 - `description`: Optional description
 - `mimeType`: Optional MIME type
+- `size`: Optional size in bytes
 
 ### Resource Contents
 

schema/schema.json

@@ -1505,6 +1505,10 @@
                     "description": "A human-readable name for this resource.\n\nThis can be used by clients to populate UI elements.",
                     "type": "string"
                 },
+                "size": {
+                    "description": "The size of the raw resource content, in bytes (i.e., before base64 encoding or any tokenization), if known.\n\nThis can be used by Hosts to display file sizes and estimate context window usage.",
+                    "type": "integer"
+                },
                 "uri": {
                     "description": "The URI of this resource.",
                     "format": "uri",

schema/schema.ts

@@ -443,6 +443,13 @@ export interface Resource extends Annotated {
    * The MIME type of this resource, if known.
    */
   mimeType?: string;
+
+  /**
+   * The size of the raw resource content, in bytes (i.e., before base64 encoding or any tokenization), if known.
+   *
+   * This can be used by Hosts to display file sizes and estimate context window usage.
+   */
+  size?: number;
 }
 
 /**