mastra-ai/mastra · error

Unsupported schema type: ${typeof schema}

Error message

Unsupported schema type: ${typeof schema}

What it means

toStandardSchema() in packages/schema-compat converts any supported schema form (Zod v3/v4, AI SDK Schema, StandardSchemaWithJSON, JSON Schema object) into a Standard Schema. Before treating the input as a plain JSON Schema object it asserts it is a non-null object or function. If the value is null, undefined, a primitive (string/number/boolean), or any other non-object type, it throws this error because there is no conversion path for it.

Source

Thrown at packages/schema-compat/src/standard-schema/standard-schema.ts:174

    });
  }

  // Check for Zod v3 schemas (need wrapping to add JSON Schema support)
  // Important: Must use isZodV3() not instanceof z3.ZodType because
  // Zod v4 schemas are also instanceof z3.ZodType due to prototype compatibility
  if (isZodV3(schema)) {
    return toStandardSchemaZodV3(schema as ZodType);
  }

  // Check for AI SDK Schema objects (Vercel's jsonSchema wrapper)
  if (isVercelSchema(schema)) {
    return toStandardSchemaAiSdk(schema as Schema<T>);
  }

  // At this point, assume it's a plain JSON Schema object
  // JSON Schema objects are plain objects with properties like 'type', 'properties', etc.
  if (schema === null || (typeof schema !== 'object' && typeof schema !== 'function')) {
    throw new Error(`Unsupported schema type: ${typeof schema}`);
  }

  // If it's a function that's not StandardSchemaWithJSON, it's not supported
  if (typeof schema === 'function') {
    throw new Error(`Unsupported schema type: function (schema libraries should implement StandardSchemaWithJSON)`);
  }

  return toStandardSchemaJsonSchema(schema as JSONSchema7);
}

/**
 * Type guard to check if a value implements the StandardSchemaV1 interface.
 *
 * @param value - The value to check
 * @returns True if the value implements StandardSchemaV1
 *
 * @example
 * ```typescript

View on GitHub (pinned to 75dd419e61)

Solutions

1. Ensure the schema variable is actually defined and imported before calling the API (check for undefined/missing imports).
2. Pass the schema object itself, not a schema name, string, or JSON string.
3. If the schema is loaded asynchronously/lazily, await or resolve it before registering the tool/agent.
4. Wrap the call in a check: if (schema == null || typeof schema !== 'object') throw a descriptive app-level error before reaching Mastra.

Example fix

// before
new Tool({ parameters: process.env.TOOL_SCHEMA as any }) // undefined or a JSON string
// after
import { z } from 'zod';
new Tool({ parameters: z.object({ query: z.string() }) })

function assertValidSchemaInput(s: unknown): void {
  if (s === null || (typeof s !== 'object' && typeof s !== 'function')) {
    throw new TypeError(`Expected a schema object, got: ${s === null ? 'null' : typeof s}`);
  }
}

const isSchemaObject = (s: unknown): s is Record<string, unknown> =>
  typeof s === 'object' && s !== null;

try {
  return toStandardSchema(schema);
} catch (e) {
  if (e.message.startsWith('Unsupported schema type')) {
    throw new Error(`Schema must be a Zod/JSON Schema/StandardSchema object, got ${typeof schema}`);
  }
  throw e;
}

When it happens

Trigger: Calling toStandardSchema (directly or via wrapped/result/rewrapped) with null, undefined, a string like 'zod-schema', a number, or a boolean instead of an actual schema object.

Common situations: Schema loaded from a lazily-initialized config that is still undefined at call time; a typo'd import yielding undefined; passing the *name* of a schema instead of the schema object; JSON.parse failure upstream returning a primitive; destructuring a tool/agent definition where the schema field is missing.

Related errors

• Unsupported schema type: function (schema libraries should i
• ${label} contains an unsupported field.
• SCHEMA_UNAVAILABLE
• Could not generate title from input ${JSON.stringify(message
• Invalid state update: ${messages}

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/a50fb6d7f9f599c9. Report an issue: GitHub.