---
title: Commands
editUrl: https://github.com/Cratis/Arc.TypeScript/edit/main/Documentation/commands/index.md
description: Change application state with Arc commands, and find the pages for validation, outcomes, context, operations, and calling commands from code.
---


Registering a task or renaming it should not require a hand-written route, body parser, validation response, and status-code mapping per endpoint. In Arc, a command is a class that carries the input and handles itself. Arc supplies the endpoint, the pipeline, the result envelope, and, through the [proxy generator](/arc/backend/typescript/proxy-generation/), a typed frontend client.

Arc is a CQRS framework, not an event store. A command's `handle()` can call a service, write through a storage integration, or return a value. It does not have to produce an event or use Chronicle.

```mermaid
flowchart LR
    Client -->|POST| Endpoint[Arc route]
    Endpoint --> Checks[Authentication, authorization, validation]
    Checks --> Handle[provide, then handle]
    Handle --> Values[Response values and operations]
    Values --> Result[CommandResult]
    Result --> Client
```

## A command

```typescript title="Features/Tasks/Registration/Registration.ts"
import { field } from '@cratis/fundamentals';
import { command } from '@cratis/arc.core';
import { TaskId } from '../TaskId.js';
import { TaskTitle } from '../TaskTitle.js';
import { Tasks } from '../Tasks.js';

@command()
export class RegisterTask {
    @field(TaskId) id!: TaskId;
    @field(TaskTitle) title!: TaskTitle;

    handle(tasks: Tasks): TaskId {
        tasks.register(this.id, this.title);
        return this.id;
    }
}
```

This is the [Tasks sample command](https://github.com/Cratis/Arc.TypeScript/blob/main/Samples/Tasks/Features/Tasks/Registration/Registration.ts). The sample's [generated metadata](/arc/backend/typescript/proxy-generation/generated-artifact-metadata/) binds the `tasks` parameter to the `Tasks` service; without it, mark `handle()` with `@inject(Tasks)`. [Your first command](/arc/backend/typescript/getting-started/your-first-command/) walks through it with its imports.

## Find your way

| Page | Use it when you want to |
| --- | --- |
| [Model-bound commands](/arc/backend/typescript/commands/model-bound/) | Declare fields, `handle()`, and `provide()`, and control a command's route |
| [Command authorization](/arc/backend/typescript/commands/model-bound/authorization/) | Restrict a command with roles, policies, or anonymous access |
| [Command validation](/arc/backend/typescript/commands/command-validation/) | Add rules with `CommandValidator` before `handle()` runs |
| [Validation severity filtering](/arc/backend/typescript/commands/validation-severity-filtering/) | Let warnings pass or block, per request |
| [Command pipeline](/arc/backend/typescript/commands/command-pipeline/) | Understand the order in which every check runs |
| [Command outcomes](/arc/backend/typescript/commands/command-outcomes/) | Return a response, reject, or deny from `provide()` and `handle()` |
| [Response value handlers](/arc/backend/typescript/commands/response-value-handlers/) | Process extra return values on the server |
| [Command context](/arc/backend/typescript/commands/command-context/) | Read the key, values, and request identity; bind the signal and context |
| [Command execution scopes](/arc/backend/typescript/commands/command-execution-scopes/) | Run code around `provide()` and `handle()`, such as a unit of work |
| [Command operations](/arc/backend/typescript/commands/operations/) | Declare side effects that Arc executes and compensates |
| [Command filters](/arc/backend/typescript/commands/command-filters/) | Validate low-level definitions with `validate` and `filters` |
| [Low-level definitions](/arc/backend/typescript/commands/low-level-definitions/) | Keep Zod-backed `defineCommand` and `defineQuery` |
| [Calling commands from code](/arc/backend/typescript/commands/calling-commands-from-code/) | Run a command or query from a job, a spec, or a Fetch API host |

To append events from a command, see the experimental [Chronicle integration](/arc/backend/typescript/chronicle/).