Standard Schema

StandardSchemaV1 is the validation boundary. A compatible schema exposes ~standard.version, vendor, optional phantom types, and a validate(value, options) function. Form cares about success values and issue lists, not the library that produced them.

type StandardSchemaV1<Input = unknown, Output = Input> = {
  readonly '~standard': {
    readonly version: 1;
    readonly vendor: string;
    readonly validate: (value: unknown, options?: unknown) =>
      | { value: Output; issues?: undefined }
      | { issues: readonly { message: string; path?: readonly unknown[] }[] };
  };
};

This makes Zod-like or Valibot-like tools possible without a direct dependency. Field-local schemas can override form-level validation for one path. Use that override for isolated field rules, not for cross-field constraints that need the whole values object.

When to care

Most applications can start with Quick start and Guides. Read this page when you build reusable abstractions, debug edge cases, or need to explain why Form chooses explicit paths, source-neutral schemas, stable keys, and normalized state instead of hiding those decisions behind a larger framework.