Tool `inputSchema` and `outputSchema` do not support JSON Schema

[jpmcb]

Describe the bug

Related: modelcontextprotocol/inspector#552

Both tool inputSchema and outputSchema do not properly support JSON Schema as they have hard coded literal object types:

typescript-sdk/src/types.ts

Lines 885 to 894 in cb4743d

	/**
	* A JSON Schema object defining the expected parameters for the tool.
	*/
	inputSchema: z
	.object({
	type: z.literal("object"),
	properties: z.optional(z.object({}).passthrough()),
	required: z.optional(z.array(z.string())),
	})
	.passthrough(),

typescript-sdk/src/types.ts

Lines 895 to 906 in cb4743d

	/**
	* An optional JSON Schema object defining the structure of the tool's output returned in
	* the structuredContent field of a CallToolResult.
	*/
	outputSchema: z.optional(
	z.object({
	type: z.literal("object"),
	properties: z.optional(z.object({}).passthrough()),
	required: z.optional(z.array(z.string())),
	})
	.passthrough()
	),

From the spec:

inputSchema: JSON Schema defining expected parameters
outputSchema: Optional JSON Schema defining expected output structure

JSON Schema may have type array, string, etc. etc.: https://json-schema.org/understanding-json-schema/reference/type

To Reproduce

1. Using the following valid JSON Schema as an outputSchema:

{
  "type": "array",
  "items": {
    "type": "object",
    "required": [ "id" ],
    "properties": {
      "id": {
        "type": "integer"
      }
    }
  }
}

2. Notice that outputSchema throws an error related to type

Expected behavior

Support any JSON Schema type

[itai-gendler]

any plans to support this? why to enforce usage of zod if one would like to just use a json schema

[jpmcb]

Hi @itai-gendler - we need to get this through the core protocol - if this is something you want, please go show some love to my proposals:

• SEP-834 Support full JSON Schema 2020-12 modelcontextprotocol#834
• SEP-834: Tools inputSchema & outputSchema conform to JSON Schema 2020-12 modelcontextprotocol#881

[felixweinberger]

Hi @itai-gendler - we need to get this through the core protocol - if this is something you want, please go show some love to my proposals:

• SEP-834 Support full JSON Schema 2020-12 modelcontextprotocol#834
• SEP-834: Tools inputSchema & outputSchema conform to JSON Schema 2020-12 modelcontextprotocol#881

Closing this as not a bug but requires a change to the protocol as described here. Please follow these if interested.