---
title: Command Contracts
---

Core command support in `@cratis/arc` is built around typed command classes generated from backend command definitions.

## ICommand

The core command interface provides execution and state-management capabilities:

```typescript
interface ICommand<TCommandContent = object, TCommandResponse = object> extends ICanBeConfigured {
    readonly route: string;
    readonly roles: string[];
    readonly propertyDescriptors: PropertyDescriptor[];
    execute(
        allowedSeverity?: ValidationResultSeverity,
        ignoreWarnings?: boolean
    ): Promise<CommandResult<TCommandResponse>>;
    validate(): Promise<CommandResult<TCommandResponse>>;
    clear(): void;
    setInitialValues(values: TCommandContent): void;
    setInitialValuesFromCurrentValues(): void;
    revertChanges(): void;
    readonly hasChanges: boolean;
    propertyChanged(property: string): void;
    onPropertyChanged(callback: PropertyChanged, thisArg: object): void;
}
```

## Change Tracking

Commands track property changes automatically.

- `hasChanges` indicates whether current values differ from the baseline.
- `setInitialValues()` sets an explicit baseline.
- `setInitialValuesFromCurrentValues()` snapshots current values as baseline.
- `revertChanges()` restores baseline values.
- `validate()` runs the server-side authorization and validation path without executing the handler.

## Property Change Notifications

Commands expose property-change callbacks for reactive flows:

```typescript
command.onPropertyChanged((property: string) => {
    console.log(`Property ${property} changed`);
});
```

## See Also

- [Validation And Results](/arc/frontend/core/commands/validation-and-results/)
- [Configuration](/arc/frontend/core/commands/configuration/)
- [React Commands](/arc/frontend/react/commands/)