Async validation fallback with `superRefine` not triggering server action

[armel-zeli-minlay]

Describe the bug and the expected behavior

Hi Conform team 👋

First of all, thank you for this fantastic library — we’ve been using it successfully with a multi-step form in React 19 and Next.js 15 (App Router). However, we’re struggling to get async validation via superRefine working live on blur, without waiting for a form submission.

---

✅ What we're trying to achieve

When the user types a laboratory name and blurs the input, we want to:

• Trigger a request to the backend (via a server action) to check if the name already exists
• Immediately display an error message if the name is already taken
• Without submitting the form or advancing the step (this is part of a multi-step flow)

We followed the official Conform async validation guide, including the conformZodMessage.VALIDATION_UNDEFINED fallback mechanism.

⏪ Before following the doc, we also tried something more naive

name: z
  .string({
    required_error: "Le nom est obligatoire",
  })
  .min(3, "Le nom est trop court")
  .superRefine((name, ctx) => {
    if (typeof window !== "undefined") {
      fetch("/api/laboratories/check-name", {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ name }),
      })
        .then((res) => res.json())
        .then((data) => {
          if (data.exists) {
            console.log("nom déjà utilisé !!!");
            ctx.addIssue({
              code: "custom",
              message: "Ce nom est déjà utilisé",
            });
          } else {
            console.log("nom disponible");
          }
        })
        .catch(() => {
          ctx.addIssue({
            code: "custom",
            message: "Erreur lors de la vérification du nom",
          });
        });
    }
  }),

The logs worked correctly, and the API was called — but Conform never displayed the error, which is expected since the validation was async in a synchronous context.

---

Conform version

v1.2.2

Steps to Reproduce the Bug or Issue

---

🧪 Here's what we've implemented

1. Zod schema with fallback superRefine

export function createInformationStepSchema(options?: {
  isLaboratoryNameTaken?: (name: string) => Promise<boolean>;
}) {
  return baseInformationStepSchema.extend({
    name: baseInformationStepSchema.shape.name.pipe(
      z.string().superRefine((name, ctx) => {
        if (!options?.isLaboratoryNameTaken) {
          ctx.addIssue({
            code: "custom",
            message: conformZodMessage.VALIDATION_UNDEFINED,
            fatal: true,
          });
          return;
        }

        return options.isLaboratoryNameTaken(name).then((taken) => {
          if (taken) {
            ctx.addIssue({
              code: "custom",
              message: "Ce nom de laboratoire est déjà utilisé",
            });
          }
        });
      }),
    ),
  });
}

2. Server action used by Conform

export async function isLaboratoryNameTaken(name: string): Promise<boolean> {
  const data = await execute(findLaboratoryByName, { name });
  const laboratories = data?.groupLaboratories || [];
  return laboratories.length > 0;
}

export async function validateInformationStep(_: unknown, formData: FormData) {
  console.log("⚠️ Server action triggered?");
  return parseWithZod(formData, {
    schema: createInformationStepSchema({ isLaboratoryNameTaken }),
    async: true,
  });
}

3. useForm and useActionState in create-form.tsx

const [lastResult, formAction] = useActionState(
  validateInformationStep,
  undefined,
);

const [form] = useForm<createLaboratorySchemaType>({
  id: formId,
  defaultValue: {
    [currentStep.key]: currentStepData,
  },
  lastResult,
  onValidate({ formData }) {
    return parseWithZod(formData, {
      schema: currentStep.schema,
    });
  },
  shouldValidate: "onBlur",
  shouldRevalidate: "onInput",
  // ⚠️ Adding `action: formAction` doesn't seem to change anything
});

🧨 The issue

• The async validation doesn't work on blur.
• The fallback server action (validateInformationStep) is never called.
• Instead, the browser performs a full page reload as soon as we blur the input (after entering a valid-enough string).
• No errors are shown and console.log in the server action never runs.

---

🧵 Summary

We are trying to perform a server-side uniqueness check via superRefine, triggered automatically on blur, using the documented VALIDATION_UNDEFINED fallback strategy — but it never works as expected, and the form reloads the page instead.

We're using:

• React 19
• Next.js 15 (App Router + Server Actions)
• Conform 1.4
• Zod

---

🙏 Question

Is there anything missing in our setup?

• Is this feature (live async validation with fallback via server action) meant to work on blur?
• If yes, could you clarify what's required to make it work properly?

Thanks so much for your help! 🙌

What browsers are you seeing the problem on?

No response

Screenshots or Videos

No response

Additional context

No response