Strict mode

Superforms is quite forgiving with missing fields in the posted data. The assumption is that if you add a field to a schema, it will sooner or later be added to the form, so the default value is applied to all missing schema fields.

But you may want to be more strict and assert that the input data must exist, otherwise something is wrong. For that, you can use strict mode when calling superValidate:

const form = await superValidate(request, zod(schema), { strict: true });

Now the following will be true:

  • Any missing required field will be reported as an error.
  • Errors will be displayed as default (can be changed with the errors option).

Catch-all schema

Some validation libraries have a “catch-all” feature, allowing extra fields to be posted and validated. Here’s an example of how to use it with Zod:

import { superValidate } from 'sveltekit-superforms';
import { zod } from 'sveltekit-superforms/adapters';
import { z } from 'zod';

const schema = z.object({
  name: z.string().min(1)
.catchall(z.number().int()); // All unknown fields should be integers

export const actions = {
  default: async ({ request }) => {
    const form = await superValidate(request, zod(schema));

    if (!form.valid) {
      return fail(400, { form });

    // Typed as string, as expected
    // All other keys are typed as number

    return { form };
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