---
title: Header
description: A bold, single-line title that breaks up a message or view into sections.
---

A header displays a short, bold line of plain text. Use it to introduce a distinct section
of a message or app surface. Slack doesn't apply any markdown to it.

<Preview
  payload={{
    blocks: [
      {
        type: "header",
        text: {
          type: "plain_text",
          text: "This is a header block",
          emoji: true,
        },
      },
    ],
  }}
/>

## Fields

| Prop | Type | Default | Description |
| - | - | - | - |
| `type` | `string` | - | Always `"header"`. |
| `text` | `plain_text object` | - | The header's text. Must be a `plain_text` text object; `mrkdwn` isn't allowed. Maximum 150 characters. |
| `block_id?` | `string` | - | A unique identifier for the block, up to 255 characters. Slack generates one if omitted. |

## Examples

### Basic header

<Preview
  payload={{
    blocks: [
      {
        type: "header",
        text: { type: "plain_text", text: "Weekly release notes", emoji: true },
      },
    ],
  }}
/>

### Header with a section and divider

Headers are typically followed by content: a section, a divider, or both.

<Preview
  payload={{
    blocks: [
      {
        type: "header",
        text: { type: "plain_text", text: "Budget Performance", emoji: true },
      },
      {
        type: "section",
        text: {
          type: "mrkdwn",
          text: "*Q3 spend* is tracking 8% under budget across all teams.",
        },
      },
      { type: "divider" },
      {
        type: "section",
        text: { type: "mrkdwn", text: "Full breakdown is attached below." },
      },
    ],
  }}
/>

:::note
This library also renders the Block Kit Builder's `level` field (1–4) on headers, which
scales the text size. It's not part of the Slack API; `level` defaults to 2, Slack's
standard header size, and only affects rendering here.
:::

## Related

**[Section](/blocks/section)**

Text, fields, and an optional accessory element.

**[Divider](/blocks/divider)**

A simple horizontal rule between blocks.

**[Context](/blocks/context)**

Small, muted supplementary text or images.