Invalid validator passed to remote function. Expected "unche

Error message

Invalid validator passed to remote function. Expected "unchecked" or a Standard Schema (https://standardschema.dev)

What it means

`create_validator` accepts only the string `'unchecked'` or an object implementing Standard Schema (`'~standard' in validator`). Anything else passed as the second argument to a remote function declaration cannot be used as a validator, so SvelteKit throws at module initialization time.

Source

Thrown at packages/kit/src/runtime/app/server/remote/shared.js:42

		return (arg) => arg;
	}

	// use https://standardschema.dev validator if provided
	if ('~standard' in validate_or_fn) {
		return async (arg) => {
			// access property and call method in one go to preserve potential this context
			const result = await validate_or_fn['~standard'].validate(arg);

			// if the `issues` field exists, the validation failed
			if (result.issues) {
				throw new ValidationError(result.issues);
			}

			return result.value;
		};
	}

	throw new Error(
		'Invalid validator passed to remote function. Expected "unchecked" or a Standard Schema (https://standardschema.dev)'
	);
}

/**
 * In case of a single remote function call, just returns the result.
 *
 * In case of a full page reload, returns the response for a remote function call,
 * either from the cache or by invoking the function.
 * Also saves an uneval'ed version of the result for later HTML inlining for hydration.
 *
 * @template {MaybePromise<any>} T
 * @param {RemoteInternals} internals
 * @param {string} payload — the stringified raw argument (i.e. the cache key the client will use)
 * @param {RequestState} state
 * @param {() => Promise<T>} get_result
 * @returns {Promise<T>}
 */

View on GitHub (pinned to 03f1687fe6)

Solutions

Pass a Standard Schema-compliant schema (zod ≥3.24, valibot, arktype) instead of a custom object/function.
Upgrade the validation library to a version exposing the `~standard` property.
Use the literal `'unchecked'` if you intentionally want no validation.
If you only want input coercion plus validation, wrap your logic in a compliant schema (e.g. `z.custom()`).

Example fix

// before
export const getUser = query((id) => db.getUser(id), (arg) => typeof arg === 'string');
// after
import { z } from 'zod';
export const getUser = query((id) => db.getUser(id), z.string());

Defensive patterns

Strategy: validation

Validate before calling

function isStandardSchema(v) {
  return v === 'unchecked' || (v && typeof v === 'object' && '~standard' in v);
}
// assert before declaring: if (!isStandardSchema(mySchema)) throw new TypeError('...');

Type guard

function isStandardSchema(v) {
  return !!v && (typeof v === 'object' || typeof v === 'function') && '~standard' in v;
}

Try / catch

// This throws at module init, so wrap the declaration site if dynamic:
try {
  const fn = query(handler, maybeSchema);
} catch (e) {
  if (e.message.includes('Invalid validator')) useUncheckedFallback();
  else throw e;
}

Prevention

Use zod >= 3.24 / valibot / arktype, which implement Standard Schema.
Pass the schema object itself, never a wrapper function or resolver.
Use the literal 'unchecked' deliberately and sparingly.
Upgrade validation libraries when migrating to remote functions.

When it happens

Trigger: Declaring `query(fn, myValidator)` where `myValidator` is a plain function, a non-Standard-Schema class instance, `undefined` with a function arg mismatch, or a validator from a library without Standard Schema support; also passing a schema built by an outdated library version lacking `~standard`.

Common situations: Using an old zod/yup version predating Standard Schema; hand-rolling a validator object; passing a resolver function instead of a schema; typos like passing `schema.shape.x` instead of the schema.

Related errors

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/6206be800e61f39c. Report an issue: GitHub.