angular · brysonbw · Aug 7, 2026
diff --git a/adev/src/content/guide/forms/signals/async-operations.md b/adev/src/content/guide/forms/signals/async-operations.md
@@ -244,7 +244,7 @@ TIP: See the [httpResource API documentation](api/common/http/httpResource) for
 
 Most applications should use `validateHttp()` for async validation. It handles HTTP requests with minimal configuration and covers the majority of use cases.
 
-`validateAsync()` is a lower-level API that exposes Angular's resource primitive directly. It offers complete control but requires more code and familiarity with Angular's resource API.
+`validateAsync()` is a lower-level API that exposes Angular's resource primitive. It supports both a simple async function for standard checks and full resource configuration for complete control, which requires more code and familiarity with Angular's resource API.
 
 Consider `validateAsync()` only when `validateHttp()` can't meet your needs. Some examples include:
 
@@ -253,9 +253,54 @@ Consider `validateAsync()` only when `validateHttp()` can't meet your needs. Som
 - **Complex retry logic** - Custom backoff strategies or conditional retries
 - **Direct resource access** - When you need the full resource lifecycle
 
-### Creating a custom validation rule
+### Using a simple async validator
 
-The `validateAsync()` function requires four properties: `params`, `factory`, `onSuccess`, and `onError`. The `params` function returns the parameters for your resource, while `factory` creates the resource:
+Pass an async validator function that receives the field context and returns validation errors or `null` or `undefined`. You can optionally supply a config object to handle debouncing, conditional execution (`when`), or error handling (`onError`):
+
+```ts
+import {Component, inject, signal} from '@angular/core';
+import {FieldContext, form, FormField, validateAsync} from '@angular/forms/signals';
+import {UsernameValidator} from './username-validator';
+
+@Component({
+  selector: 'app-registration',
+  imports: [FormField],
+  template: `...`,
+})
+export class Registration {
+  registrationModel = signal({username: ''});
+  private usernameValidator = inject(UsernameValidator);
+
+  registrationForm = form(this.registrationModel, (schemaPath) => {
+    validateAsync(schemaPath.username, (ctx) => this.validateUsername(ctx), {
+      debounce: 300,
+      when: ({value}) => value().length >= 3,
+      onError: (error) => ({
+        kind: 'serverError',
+        message: 'Could not verify username',
+      }),
+    });
+  });
+
+  private async validateUsername({value}: FieldContext<string>) {
+    const result = await this.usernameValidator.checkAvailability(value());
+
+    return result?.available ? null : {kind: 'usernameTaken', message: 'Username taken'};
+  }
+}
+```
+
+#### Optional Configuration Options
+
+| **Config Option** | **Type**                  | **Description**                                                                                                        |
+| ----------------- | ------------------------- | ---------------------------------------------------------------------------------------------------------------------- |
+| `debounce`        | `number \| DebounceTimer` | Duration in milliseconds to wait before triggering the async operation, or a function returning a timing promise.      |
+| `when`            | `LogicFn`                 | A function that receives the field context and returns `true` if the async validation should run.                      |
+| `onError`         | `Function`                | A handler for errors thrown by the validator. Defaults to an `{ kind: 'asyncError', message: ... }` object if omitted. |
+
+### Using Resouce-based validator
+
+For advanced control, pass an options object containing `params`, `factory`, `onSuccess`, and `onError`. The params function returns parameters for your resource, while `factory` creates the resource:
 
 ```ts
 import {Component, inject, signal, resource, Signal} from '@angular/core';

diff --git a/adev/src/content/guide/forms/signals/validation.md b/adev/src/content/guide/forms/signals/validation.md
@@ -492,6 +492,61 @@ NOTE: Child fields also have a `key` signal, and array item fields have both `ke
 
 Return an error object with `kind` and `message` when validation fails. Return `null` or `undefined` when validation passes.
 
+### Using validateAsync()
+
+The `validateAsync()` function creates custom asynchronous validation rules. It receives a validator function that accesses the field context and returns a `Promise` resolving to:
+
+| Return Value          | Meaning          |
+| --------------------- | ---------------- |
+| Error object          | Value is invalid |
+| `null` or `undefined` | Value is valid   |
+
+```angular-ts
+import {Component, inject, signal} from '@angular/core';
+import {FieldContext, form, FormField, validateAsync} from '@angular/forms/signals';
+import {UserService} from './user.service';
+
+@Component({
+  selector: 'app-username-form',
+  imports: [FormField],
+  template: `
+    <form novalidate>
+      <label>
+        Username
+        <input [formField]="usernameForm.username" />
+      </label>
+    </form>
+  `,
+})
+export class UsernameFormComponent {
+  private userService = inject(UserService);
+
+  usernameModel = signal({username: ''});
+
+  usernameForm = form(this.usernameModel, (schemaPath) => {
+    validateAsync(schemaPath.username, (ctx) => this.validateUsername(ctx));
+  });
+
+  private async validateUsername({value}: FieldContext<string>) {
+    const username = value();
+    const available = await this.userService.checkUsernameAvailability(username);
+
+    if (!available) {
+      return {
+        kind: 'usernameTaken',
+        message: 'Username is already taken',
+      };
+    }
+
+    return null;
+  }
+}
+```
+
+The validator function receives the same `FieldContext` object as synchronous `validate()`.
+
+NOTE: For advanced async validation and complex scenarios requiring execution delays, conditional checks, unhandled error fallbacks, or direct access to Angular's `resource()` primitive, see the [Custom async validation with validateAsync() guide](guide/forms/signals/async-operations#custom-async-validation-with-validateasync).
+
 ### Using validateTree()
 
 The `validateTree()` function creates custom validation rules that can target multiple fields or provide complex validation logic for a whole subtree.
@@ -505,9 +560,7 @@ interface User {
   lastName: string;
 }
 
-@Component({
-  /* ... */
-})
+@Component({/* ... */})
 export class UserFormComponent {
   readonly userModel = model<User>({
     firstName: '',
@@ -750,9 +803,7 @@ import {Component, computed, signal} from '@angular/core';
 import {form, FormField, validateStandardSchema} from '@angular/forms/signals';
 import z from 'zod';
 
-@Component({
-  /* ... */
-})
+@Component({/* ... */})
 export class DynamicSchema {
   model = signal({document: '', type: 'dni'});
 

diff --git a/packages/forms/signals/src/api/rules/validation/validate_async.ts b/packages/forms/signals/src/api/rules/validation/validate_async.ts
@@ -6,13 +6,22 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
-import {DebounceTimer, Resource, Signal, computed, debounced, ɵchain} from '@angular/core';
+import {
+  DebounceTimer,
+  Resource,
+  resource,
+  Signal,
+  computed,
+  debounced,
+  ɵchain,
+} from '@angular/core';
 import {FieldNode} from '../../../field/node';
 import {addDefaultField} from '../../../field/validation';
 import {FieldPathNode} from '../../../schema/path_node';
 import {assertPathIsCurrent} from '../../../schema/schema';
 import {
   FieldContext,
+  FieldValidatorAsync,
   LogicFn,
   PathKind,
   SchemaPath,
@@ -117,19 +126,167 @@ export interface AsyncValidatorOptions<
  * @param opts The async validation options.
  * @template TValue The type of value stored in the field being validated.
  * @template TParams The type of parameters to the resource.
- * @template TResult The type of result returned by the resource
- * @template TPathKind The kind of path being validated (a root path, child path, or item of an array)
+ * @template TResult The type of result returned by the resource.
+ * @template TPathKind The kind of path being validated (a root path, child path, or item of an array).
  *
  * @see [Signal Form Async Validation](guide/forms/signals/validation#async-validation)
  * @see [Custom async validation](guide/forms/signals/async-operations#custom-async-validation-with-validateasync)
+ * @see [Custom validation rules](guide/forms/signals/validation#using-validateasync)
  * @category validation
  * @publicApi 22.0
  */
 export function validateAsync<TValue, TParams, TResult, TPathKind extends PathKind = PathKind.Root>(
   path: SchemaPath<TValue, SchemaPathRules.Supported, TPathKind>,
   opts: AsyncValidatorOptions<TValue, TParams, TResult, TPathKind>,
+): void;
+
+/**
+ * Adds async validation to the field corresponding to the given path using a simple validator function.
+ *
+ * @param path A path indicating the field to bind the async validation logic to.
+ * @param logic A validator function that returns the validation errors asynchronously.
+ * @param config Optional, allows providing any of the following options for the async validation over the simple validator function:
+ *  - `debounce`: Duration in milliseconds to wait before triggering the async operation, or a function that
+ *    returns a promise that resolves when the update should proceed.
+ *  - `when`: A function that receives the field context and returns true if the async validation should be run.
+ *  - `onError`: A function to handle errors thrown by the async validator (HTTP errors, network errors, etc.).
+ *    Receives the error and the field context, returns a list of validation errors.
+ * @template TValue The type of value stored in the field being validated.
+ * @template TPathKind The kind of path being validated (a root path, child path, or item of an array).
+ *
+ * @see [Signal Form Async Validation](guide/forms/signals/validation#async-validation)
+ * @see [Custom async validation](guide/forms/signals/async-operations#custom-async-validation-with-validateasync)
+ * @see [Custom validation rules](guide/forms/signals/validation#using-validateasync)
+ * @category validation
+ * @publicApi 22.0
+ */
+export function validateAsync<TValue, TPathKind extends PathKind = PathKind.Root>(
+  path: SchemaPath<TValue, SchemaPathRules.Supported, TPathKind>,
+  logic: NoInfer<FieldValidatorAsync<TValue, TPathKind>>,
+  config?: {
+    debounce?: DebounceTimer<FieldContext<TValue, TPathKind> | undefined>;
+    when?: NoInfer<LogicFn<TValue, boolean, TPathKind>>;
+    onError?: (error: unknown, ctx: FieldContext<TValue, TPathKind>) => TreeValidationResult;
+  },
+): void;
+
+/**
+ * Internal implementation for registering async validation on a field via resource options
+ * or a simple validator function.
+ *
+ * @param path A path indicating the field to bind the async validation logic to.
+ * @param optsOrLogic Either an object with full resource validator options or a simple async validator function.
+ * @param config Optional, allows providing any of the following options for the async validation over the simple validator function:
+ *  - `debounce`: Duration in milliseconds to wait before triggering the async operation, or a function that
+ *    returns a promise that resolves when the update should proceed.
+ *  - `when`: A function that receives the field context and returns true if the async validation should be run.
+ *  - `onError`: A function to handle errors thrown by the async validator (HTTP errors, network errors, etc.).
+ *    Receives the error and the field context, returns a list of validation errors.
+ * @template TValue The type of value stored in the field being validated.
+ * @template TParams The type of parameters to the resource.
+ * @template TResult The type of result returned by the resource.
+ * @template TPathKind The kind of path being validated (a root path, child path, or item of an array).
+ *
+ * @internal
+ */
+export function validateAsync<
+  TValue,
+  TParams = unknown,
+  TResult = unknown,
+  TPathKind extends PathKind = PathKind.Root,
+>(
+  path: SchemaPath<TValue, SchemaPathRules.Supported, TPathKind>,
+  optsOrLogic:
+    | AsyncValidatorOptions<TValue, TParams, TResult, TPathKind>
+    | FieldValidatorAsync<TValue, TPathKind>,
+  config?: {
+    debounce?: DebounceTimer<FieldContext<TValue, TPathKind> | undefined>;
+    when?: NoInfer<LogicFn<TValue, boolean, TPathKind>>;
+    onError?: (error: unknown, ctx: FieldContext<TValue, TPathKind>) => TreeValidationResult;
+  },
 ): void {
   assertPathIsCurrent(path);
+
+  if (typeof optsOrLogic === 'function') {
+    const logic = optsOrLogic;
+    const configOpts = config ?? {};
+
+    // Check if debounce option is a function, wrap it to pass the field context and last value.
+    const debounce =
+      typeof configOpts.debounce === 'function'
+        ? (
+            value: {ctx: FieldContext<TValue, TPathKind>; value: TValue} | undefined,
+            lastValue: unknown,
+          ) => (configOpts.debounce as Function)(value?.ctx, lastValue)
+        : configOpts.debounce;
+
+    // Map the simple validator function to the full AsyncValidatorOptions structure.
+    // Reading `ctx.value()` inside `params` ensures signal dependencies are tracked
+    // so the resource loader re-runs whenever the field value changes.
+    const mappedOpts: AsyncValidatorOptions<
+      TValue,
+      {ctx: FieldContext<TValue, TPathKind>; value: TValue} | undefined,
+      TreeValidationResult | undefined,
+      TPathKind
+    > = {
+      params: (ctx: FieldContext<TValue, TPathKind>) => ({
+        ctx,
+        value: ctx.value(),
+      }),
+      debounce: debounce as DebounceTimer<
+        {ctx: FieldContext<TValue, TPathKind>; value: TValue} | undefined
+      >,
+      factory: (
+        paramsSignal: Signal<{ctx: FieldContext<TValue, TPathKind>; value: TValue} | undefined>,
+      ) =>
+        resource({
+          params: () => paramsSignal(),
+          loader: async ({
+            params,
+          }: {
+            params: {ctx: FieldContext<TValue, TPathKind>; value: TValue} | undefined;
+          }) => {
+            if (!params) return undefined;
+            const res = await logic(params.ctx);
+            return res as TreeValidationResult | undefined;
+          },
+        }),
+      onSuccess: (result: TreeValidationResult | undefined) => result,
+      onError:
+        configOpts.onError ??
+        ((error: unknown) => ({
+          kind: 'asyncError',
+          message: String(error ?? 'Async validation failed'),
+        })),
+      when: configOpts.when,
+    };
+
+    registerAsyncResourceValidator(path, mappedOpts);
+    return;
+  }
+
+  registerAsyncResourceValidator(path, optsOrLogic);
+}
+
+/**
+ * Registers an async resource validator for the given path and options.
+ *
+ * @template TValue The type of value stored in the field being validated.
+ * @template TParams The type of parameters to the resource.
+ * @template TResult The type of result returned by the resource
+ * @template TPathKind The kind of path being validated (a root path, child path, or item of an array)
+ * @param path
+ * @param opts
+ */
+function registerAsyncResourceValidator<
+  TValue,
+  TParams,
+  TResult,
+  TPathKind extends PathKind = PathKind.Root,
+>(
+  path: SchemaPath<TValue, SchemaPathRules.Supported, TPathKind>,
+  opts: AsyncValidatorOptions<TValue, TParams, TResult, TPathKind>,
+): void {
   const pathNode = FieldPathNode.unwrapFieldPath(path);
 
   const RESOURCE = createManagedMetadataKey<ReturnType<typeof opts.factory>, TParams | undefined>(

diff --git a/packages/forms/signals/src/api/types.ts b/packages/forms/signals/src/api/types.ts
@@ -900,6 +900,26 @@ export type FieldValidator<TValue, TPathKind extends PathKind = PathKind.Root> =
   TPathKind
 >;
 
+/**
+ * A function that takes the `FieldContext` for the field being validated and returns a
+ * `ValidationResult` or pending status indicating errors for the field asynchronously.
+ *
+ * @template TValue The type of value stored in the field being validated
+ * @template TPathKind The kind of path being validated (root field, child field, or item of an array)
+ *
+ * @see [Custom validation rules](guide/forms/signals/validation#using-validateasync)
+ *
+ * @category validation
+ * @publicApi 22.0
+ */
+export type FieldValidatorAsync<TValue, TPathKind extends PathKind = PathKind.Root> = LogicFn<
+  TValue,
+  | ValidationResult<ValidationError.WithoutFieldTree>
+  | Promise<ValidationResult<ValidationError.WithoutFieldTree>>
+  | 'pending',
+  TPathKind
+>;
+
 /**
  * A function that takes the `FieldContext` for the field being validated and returns a
  * `TreeValidationResult` indicating errors for the field and its sub-fields.