Change Icon.sizes from string to string array (modelcontextprotocol#1531)

* Add SDK Support Tiers section to priority areas

Introduces standardized tiering system for MCP SDKs based on:
- Specification compliance
- Maintenance quality
- Update frequency

Defines three tiers to help developers choose appropriate SDKs and provide clear improvement pathways for maintainers.

* Change Icon.sizes from string to string array

The Icon.sizes field was previously defined as a space-separated string
(e.g., "48x48 96x96"), which was ambiguous and error-prone to parse.

Changed to string[] format (e.g., ["48x48", "96x96"]) for clarity and
consistency. Each size is now a discrete array element, making it easier
to iterate over and validate individual size specifications.

This maintains compatibility with the "any" keyword for scalable formats
while providing a cleaner, more structured representation.

Co-Authored-By: Claude <[email protected]>

---------

Co-authored-by: Claude <[email protected]>

Author: dsp-ant

docs/specification/draft/basic/index.mdx

@@ -158,7 +158,7 @@ Icons are represented as an array of `Icon` objects, where each icon includes:
   - An HTTP/HTTPS URL pointing to an image file
   - A data URI with base64-encoded image data
 - `mimeType`: Optional MIME type if the server's type is missing or generic
-- `sizes`: Optional size specification (e.g., "48x48", "any" for scalable formats like SVG, or "48x48 96x96" for multiple sizes)
+- `sizes`: Optional array of size specifications (e.g., `["48x48"]`, `["any"]` for scalable formats like SVG, or `["48x48", "96x96"]` for multiple sizes)
 
 **Required MIME type support:**
 

docs/specification/draft/basic/lifecycle.mdx

@@ -74,7 +74,7 @@ The client **MUST** initiate this phase by sending an `initialize` request conta
         {
           "src": "https://example.com/icon.png",
           "mimeType": "image/png",
-          "sizes": "48x48"
+          "sizes": ["48x48"]
         }
       ],
       "websiteUrl": "https://example.com"
@@ -112,7 +112,7 @@ The server **MUST** respond with its own capabilities and information:
         {
           "src": "https://example.com/server-icon.svg",
           "mimeType": "image/svg+xml",
-          "sizes": "any"
+          "sizes": ["any"]
         }
       ],
       "websiteUrl": "https://example.com/server"

docs/specification/draft/schema.mdx

@@ -88,7 +88,7 @@ supports [pagination](/specification/draft/server/utilities/pagination).
           {
             "src": "https://example.com/review-icon.svg",
             "mimeType": "image/svg+xml",
-            "sizes": "any"
+            "sizes": ["any"]
           }
         ]
       }

docs/specification/draft/server/prompts.mdx

@@ -120,7 +120,7 @@ supports [pagination](/specification/draft/server/utilities/pagination).
           {
             "src": "https://example.com/rust-file-icon.png",
             "mimeType": "image/png",
-            "sizes": "48x48"
+            "sizes": ["48x48"]
           }
         ]
       }

docs/specification/draft/server/resources.mdx

@@ -98,7 +98,7 @@ To discover available tools, clients send a `tools/list` request. This operation
           {
             "src": "https://example.com/weather-icon.png",
             "mimeType": "image/png",
-            "sizes": "48x48"
+            "sizes": ["48x48"]
           }
         ]
       }

docs/specification/draft/server/tools.mdx

@@ -313,12 +313,12 @@ export interface Icon {
   mimeType?: string;
 
   /**
-   * Optional string that specifies one or more sizes at which the icon can be used.
-   * For example: `"48x48"`, `"48x48 96x96"`, or `"any"` for scalable formats like SVG.
+   * Optional array of strings that specify sizes at which the icon can be used.
+   * Each string should be in WxH format (e.g., `"48x48"`, `"96x96"`) or `"any"` for scalable formats like SVG.
    *
    * If not provided, the client should assume that the icon can be used at any size.
    */
-  sizes?: string;
+  sizes?: string[];
 }
 
 /**