Incompatible with Zod 4 #107
Description
Description
When using Zod schemas with server.tool(), the tools/list response returns empty properties: {} in the inputSchema instead of the actual schema properties. This suggests the package is missing Zod-to-JSON-Schema conversion logic.
Minimal Reproduction Code
// app/api/[transport]/route.ts
import { createMcpHandler } from "mcp-handler";
import { z } from "zod";
const handler = createMcpHandler(
(server) => {
server.tool(
"test_tool",
"Test tool with Zod schema",
{
name: z.string().describe("A name parameter"),
count: z.number().min(1).max(10).describe("A count parameter")
},
async ({ name, count }) => ({
content: [{ type: "text", text: `Hello ${name}, count: ${count}` }]
})
);
},
{},
{ basePath: "/api" }
);
export { handler as GET, handler as POST };
Expected Behavior
The tools/list response should show schema like this:
{
"inputSchema": {
"type": "object",
"properties": {
"name": {
"type": "string",
"description": "A name parameter"
},
"count": {
"type": "number",
"minimum": 1,
"maximum": 10,
"description": "A count parameter"
}
},
"required": ["name", "count"]
}
}
Actual Behavior
The tools/list response actually like this:
event: message
data: {"result":{"tools":[{"name":"test_tool","description":"Test tool with Zod schema","inputSchema":{"type":"object","properties":{},"additionalProperties":false,"$schema":"http://json-schema.org/draft-07/schema#"}}]},"jsonrpc":"2.0","id":1}
Environment
"mcp-handler": "1.0.2",
"zod": "4.1.9"