With the ever growing list of MCP servers and supported tools, it is hard to spot the right tool. With the v1.0 release of the official MCP C# SDK, you can make it a little bit easier to discover your tools thanks to the introduction of icon support — tools, resources, and prompts can now carry icon metadata that clients can display in their UIs.
Because a picture is worth a thousand words
MCP servers expose tools, resources, and prompts through list endpoints (tools/list, resources/list, prompts/list). Up until now, those lists were purely textual — names and descriptions. With icons, client applications like MCP Inspector or AI agent UIs can render visual identifiers alongside each item, making large tool catalogs much easier to navigate at a glance.
The simple case: a single icon via attribute
The quickest way to add an icon to a tool is through the IconSource parameter on the [McpServerTool] attribute:
The same IconSource parameter is available on [McpServerResource], [McpServerResourceTemplate], and [McpServerPrompt] — so the pattern is consistent across all three primitives.
The advanced case: multiple icons with metadata
For production scenarios you'll typically want more control: separate icons for light and dark themes, specific size hints, and explicit MIME types. This is done via McpServerToolCreateOptions.Icons when registering tools programmatically:
Each Icon object supports four properties:
| Property | Purpose |
Source | URL of the image |
MimeType | e.g. image/svg+xml, image/png |
| Sizes | e.g. "any", "256x256" (follows the Web App Manifest spec) |
Theme | "light" or "dark" |
Server and client identity icons
Icons aren't limited to tools, resources, and prompts. The Implementation class — used to describe the server or client itself during the MCP handshake — now also supports Icons and a WebsiteUrl:
This makes server identity richer in clients that display connected server information.
Tips for choosing icons
A few practical suggestions when picking icon assets:
- Use SVGs where possible. They scale cleanly at any size and are tiny over the wire. The `Sizes = ["any"]` hint signals that an SVG is resolution-independent.
- Provide both themes. If your client audience uses both light and dark modes, supply two icon entries. Clients that don't understand the `Theme` field will fall back to the first icon.
- Leverage Fluent Emoji. The examples in the official SDK use the microsoft/fluentui-emoji repo on GitHub, which is a great free source of consistently styled SVG and PNG icons for .NET-adjacent projects.
- Host icons on a reliable CDN. Icons are fetched by clients at runtime using the URL you provide, so availability matters.
Seeing it in action
The MCP Inspector already renders these icons. If you set up icons and connect your server to the Inspector, you'll see them appear next to each tool, resource, or prompt in the list view — giving a quick, recognizable visual handle for each capability your server exposes.
