# Radio

> Single radio option; compose with RadioGroup for sets.

- Status: beta
- Group: form
- Page: https://www.digitaltableteur.com/design-system/components/radio
- Contract: https://www.digitaltableteur.com/contracts/v1/Radio.contract.json

## When to use

Radio is one labelled option of an exclusive set. It is a low-level atom: in almost every case reach for RadioGroup, which owns the fieldset legend, the shared name, and the selection state. Use Radio directly only when composing a custom exclusive control.

## When not to use

The contract records no forbidden uses.

## Look-alikes

- Checkbox: Do not render a lone radio; a choice with one option is a Checkbox.

## Props

| Prop | Type | Default | Description | Required |
| --- | --- | --- | --- | --- |
| `label` | `string` | none | Option label. | Yes |
| `value` | `string` | none | Submitted value when selected. | Yes |
| `name` | `string` | none | Group name; must match siblings to form the exclusive set. | Yes |
| `checked` | `boolean` | none | Checked state (controlled); use inside RadioGroup for sets. | No |
| `defaultChecked` | `boolean` | none | Initial checked state (uncontrolled mode only) | No |
| `disabled` | `boolean` | `false` | Disables interaction and dims the control. | No |
| `size` | `"sm" \| "md" \| "lg" \| "S" \| "M" \| "L"` | `md` | Control hit area. | No |
| `onCheckedChange` | `(checked: boolean) => void` | none | Fired with the next checked value when selection changes. | No |
| `showLabel` | `boolean` | `true` | Render the visible label. | No |

## Variants

- Available sizes: `sm`, `md`, `lg`, `S`, `M`, `L` (default `sm`).

## Invalid combinations

- MUST NOT: `checked` and `defaultChecked` set together. `checked` makes the component controlled and `defaultChecked` uncontrolled; pass one, not both.

## Keyboard

The contract records no keyboard interaction.

## Rules

Every item under When not to use is a MUST NOT. MUST and SHOULD follow RFC 2119.

| Level | Rule | How it is checked |
| --- | --- | --- |
| MUST NOT | `checked` and `defaultChecked` set together. `checked` makes the component controlled and `defaultChecked` uncontrolled; pass one, not both. | Checked by the MCP tool validate_component_usage. |
| MUST | Required stories produce no axe violations at the configured severity. | Automated by `npm run test:stories:matrix:ci`. WCAG 2.5.8. |
| MUST | The accessibility tree (role, name, state) matches the committed snapshot for every required story. | Automated by `npm run test:stories:matrix:ci`. WCAG 1.3.1, 4.1.2. |
| MUST | The component remains legible and operable under a real browser forced-colors: active pass. | Automated by `npm run test:stories:hc`. |
| MUST | A human completed an end-to-end accessibility review of this component. | Manual review, last on 2026-05-28. |
| SHOULD | Give every radio in a set the same name so the browser enforces exclusivity. | Not stated in the contract. |
| SHOULD | Prefer RadioGroup for sets; it wires the legend, selection state, and error text. | Not stated in the contract. |
| SHOULD | Use defaultChecked for uncontrolled forms that read values on submit. | Not stated in the contract. |
| SHOULD | Keep labels short and parallel; the group's legend carries the question. | Not stated in the contract. |
| SHOULD NOT | Do not render a lone radio; a choice with one option is a Checkbox. | Not stated in the contract. |
| SHOULD NOT | Do not set checked without onCheckedChange; a controlled radio that cannot change traps keyboard users. | Not stated in the contract. |
| MUST NOT | Maintainers: Do not bypass design tokens or skip forced-colors verification at beta. | Release review; not machine-checked. |

## Install and import

- Install: `npm install @digitaltableteur/react` (version 0.9.1, restricted access on npm).
- Import: `import { Radio } from "@digitaltableteur/react";`
- Entry point: `@digitaltableteur/react/forms` exports it too.
- Styles: import `@digitaltableteur/react/style.css` once at the app boundary.
- Also available as the custom element `<dt-radio>`; see the custom elements manifest.

## Links

- Machine-readable contract (Design System Contract 1.0): https://www.digitaltableteur.com/contracts/v1/Radio.contract.json
- Markdown version of this page: https://www.digitaltableteur.com/design-system/components/radio.md
- Component index as JSON: https://www.digitaltableteur.com/design-system/components.json
- All components: https://www.digitaltableteur.com/design-system/components
- Source: The implementation lives in a private repository. This page, its Markdown twin and the contract are generated from it at build time and are the public source of truth.