# Validation

{% hint style="success" %}
This is the official documentation of Forest Admin Cloud.
{% endhint %}

Most data sources can import validation rules directly. For example, in a SQL database, columns defined as `VARCHAR(15)` will automatically include a rule to ensure content is shorter than 15 characters. Similarly, columns marked as `NOT NULL` will require that some content is always present.

***

To make the code easier to read, all the code snippets below should be wrapped in the following code. Ensure you update the collection and field names as needed.

```typescript
import type { Agent } from '@forestadmin/forest-cloud';
import { Schema } from '../typings';

export default function customizeAgent(agent: Agent<Schema>) {
  agent.customizeCollection('users', (collection) => {
    // Insert the code snippet here.
  });
}
```

***

In some cases, it might be necessary to enforce stricter rules than the ones currently set in your data source. This can be achieved through the use of the `addFieldValidation` method.

```typescript
collection
  .addFieldValidation('first_name', 'Present')
  .addFieldValidation('first_name', 'LongerThan', 2)
  .addFieldValidation('first_name', 'ShorterThan', 13)
  .addFieldValidation('first_name', 'Match', /^[a-z]+$/i);
```