Create 9.precognition.md

Author: GautierDele

content/4.digging-deeper/9.precognition.md

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+---
+title: Precognition 
+---
+Laravel Rest API supports [Laravel’s Precognition](https://laravel.com/docs/precognition) feature for live frontend validation.  
+Precognition allows you to anticipate the outcome of an HTTP request by running validation rules without executing the controller logic.  
+In other words, the request is “simulated” purely for validation.
+
+## Installation
+
+Precognition support is disabled by default. To enable it, set `rest.precognition.enabled` to true in your config/rest.php.
+:
+```php
+// config/rest.php
+'precognition' => [
+    'enabled' => true,
+],
+```
+
+This flag toggles Laravel’s `HandlePrecognitiveRequests` middleware support.
+
+## Usage Example
+
+Once enabled, any API endpoint generated via `Rest::resource` will automatically have `HandlePrecognitiveRequests` applied.  
+This means that any request with the `Precognition` header to true will be considered precognitive.  
+For example, consider a search endpoint on the users resource. If the client sends:
+
+```http request
+POST /api/users/search
+Precognition: true
+Content-Type: application/json
+
+{
+    "search": {
+        // ... search parameters ...
+    }
+}
+```
+
+Laravel will execute all middleware and run the form request or validator rules as usual, then immediately return the validation result. In this mode:
+- If the data fails validation, you will receive a 422 Unprocessable Entity with the validation errors.
+- If it passes validation, you will receive a 200 OK response and no database action is taken.
+
+In short, the request is validated but the controller method is never called, allowing you to get “live” validation feedback from the API without performing the actual operation.