modelcontextprotocol/servers · error · Error

Invalid resourceType: ${args?.resourceType}. Must be ${RESOU

Error message

Invalid resourceType: ${args?.resourceType}. Must be ${RESOURCE_TYPE_TEXT} or ${RESOURCE_TYPE_BLOB}.

What it means

Thrown by the `get-resource-reference` tool when `resourceType` is not in RESOURCE_TYPES. Unlike the prompt variant, this tool's zod schema (`z.enum(["Text","Blob"]).default("Text")`) already constrains the value, so reaching this throw means the schema default was bypassed or args were passed unvalidated.

Source

Thrown at src/everything/tools/get-resource-reference.ts:60

 * The registered tool validates and processes arguments for retrieving a resource
 * reference. Supported resource types include predefined `RESOURCE_TYPE_TEXT` and
 * `RESOURCE_TYPE_BLOB`. The retrieved resource's reference will include the resource
 * ID, type, and its associated URI.
 *
 * The tool performs the following operations:
 * 1. Validates the `resourceType` argument to ensure it matches a supported type.
 * 2. Validates the `resourceId` argument to ensure it is a finite positive integer.
 * 3. Constructs a URI for the resource based on its type (text or blob).
 * 4. Retrieves the resource and returns it in a content block.
 *
 * @param {McpServer} server - The McpServer instance where the tool will be registered.
 */
export const registerGetResourceReferenceTool = (server: McpServer) => {
  server.registerTool(name, config, async (args): Promise<CallToolResult> => {
    // Validate resource type argument
    const { resourceType } = args;
    if (!RESOURCE_TYPES.includes(resourceType)) {
      throw new Error(
        `Invalid resourceType: ${args?.resourceType}. Must be ${RESOURCE_TYPE_TEXT} or ${RESOURCE_TYPE_BLOB}.`
      );
    }

    // Validate resourceId argument
    const resourceId = Number(args?.resourceId);
    if (
      !Number.isFinite(resourceId) ||
      !Number.isInteger(resourceId) ||
      resourceId < 1
    ) {
      throw new Error(
        `Invalid resourceId: ${args?.resourceId}. Must be a finite positive integer.`
      );
    }

    // Get resource based on the resource type
    const uri =

View on GitHub (pinned to 76d64c822f)

Solutions

Let the tool's input schema do its job: omit `resourceType` to get the `"Text"` default, or pass `"Text"`/`"Blob"`.
If invoking the handler directly in tests, pass args that satisfy GetResourceReferenceSchema.
Keep the manual guard in sync with the zod enum so the two cannot diverge.

Example fix

// before
toolHandler({ resourceType: 'text', resourceId: 1 });
// after
toolHandler({ resourceType: 'Text', resourceId: 1 });

Defensive patterns

Strategy: type-guard

Validate before calling

import { RESOURCE_TYPES } from '../resources/templates.js';
// the tool's zod schema already enforces this; rely on schema-routed calls
const args = GetResourceReferenceSchema.parse(rawArgs); // throws ZodError before runtime guard

Type guard

function isResourceType(v: unknown): v is 'Text' | 'Blob' {
  return v === 'Text' || v === 'Blob';
}

Prevention

Let the SDK route args through GetResourceReferenceSchema; don't call the handler with raw objects.
In tests, build args via schema.parse so they match real routing.
Keep the manual guard and the zod enum in sync if you refactor.

When it happens

Trigger: Calling the `get-resource-reference` tool with a `resourceType` outside `"Text"`/`"Blob"` — typically only reachable if the tool is invoked with raw unvalidated args (bypassing zod parse) or if RESOURCE_TYPES is mutated. Normal SDK-routed calls go through the schema first.

Common situations: Direct unit tests invoking the handler with crafted args, schema bypass in custom transports, or a future refactor that drops the zod enum while keeping the manual guard.

Related errors

AI-assisted analysis of modelcontextprotocol/servers@76d64c822f (2026-08-12). Data as JSON: /api/errors/d946901940b8ab60. Report an issue: GitHub.