When registering a tool using server.tool, like in the example below:

server.tool(
  "get-neme",
  {
    slug: z.string().min(1).describe("The slug of the neme"),
  } as ToolAnnotations,
  async ({ slug }) => {
    return {
      content: [{ type: "text", text: `${slug}` }],
    };
  }
);

The returned object should conform to the RegisteredTool type, which includes the inputSchema. However, in practice, inputSchema is always undefined.
This causes issues with the MCP Client, specifically the MCP Inspector, which relies on inputSchema to display and send input arguments. Without it, tools are effectively unusable via the default MCP Client interface.

Current Workaround

The only way to make the tool usable in the MCP Client is to manually modify the server.tool call to ensure inputSchema is properly populated.

const tool = server.tool(
  "get-neme",
  {
    slug: z.string().min(1).describe("The slug of the neme"),
  } as ToolAnnotations,
  async ({ slug }) => {
    return {
      content: [{ type: "text", text: `${slug}` }],
    };
  }
);

Object.assign(tool, {
  inputSchema: z.object({
    slug: z.string().min(1).describe("The slug of the neme"),
  }),
});