/slack-block-kit

Block Types — Complete Property Reference

Sources:

• Block Kit Blocks — Slack
• Block Kit Reference — Slack
• Markdown block — Slack
• March 2026 Block Kit rich-text rollout — Slack

All 21 block types with full property tables, constraints, and surface compatibility.

Table of Contents

Current surface compatibility

This matrix follows Slack's live block index. Do not infer compatibility from an example rendered on a different surface.

The file block is returned when retrieving messages with remote files; apps cannot add it directly to a surface.

For block types that support and retain block_id, keep it at 255 characters or fewer, make it unique within the payload, and use a new value for each updated iteration of a message or view. Slack normally generates one when it is omitted. The markdown block is the exception: its block_id is ignored and not retained, so do not rely on a supplied or generated ID for that block. Modal input-state preservation is a deliberate update exception described in SURFACES.md.

1. Header Block

Large, bold text for section titles.

Surfaces: Messages, Modals, Home tabs

{
  "type": "header",
  "text": { "type": "plain_text", "text": "Section Title", "emoji": true }
}

2. Section Block

Primary content block with text, fields, and accessory.

Surfaces: Messages, Modals, Home tabs

Compatible accessories: button, overflow, datepicker, timepicker, select menus, multi-select menus, checkboxes, radio_buttons, image, workflow_button.

{
  "type": "section",
  "text": { "type": "mrkdwn", "text": "*Status:* Active" },
  "accessory": {
    "type": "button",
    "text": { "type": "plain_text", "text": "View" },
    "action_id": "view_btn",
    "value": "view"
  }
}

Fields layout renders as two columns:

{
  "type": "section",
  "fields": [
    { "type": "mrkdwn", "text": "*Status:*\nActive" },
    { "type": "mrkdwn", "text": "*Owner:*\nChris" }
  ]
}

3. Divider Block

Horizontal rule separator.

Surfaces: Messages, Modals, Home tabs

{ "type": "divider" }

4. Context Block

Small, muted metadata.

Surfaces: Messages, Modals, Home tabs

{
  "type": "context",
  "elements": [
    { "type": "image", "image_url": "https://example.com/pin.png", "alt_text": "pin" },
    { "type": "mrkdwn", "text": "Location: *Dogpatch*" }
  ]
}

5. Actions Block

Container for interactive elements.

Surfaces: Messages, Modals, Home tabs

Compatible elements: button, select menus, multi-select menus, overflow, datepicker, datetimepicker, timepicker, checkboxes, radio_buttons, workflow_button.

{
  "type": "actions",
  "elements": [
    {
      "type": "datepicker",
      "action_id": "date_pick",
      "initial_date": "2026-02-09",
      "placeholder": { "type": "plain_text", "text": "Select date" }
    },
    {
      "type": "button",
      "text": { "type": "plain_text", "text": "Submit" },
      "style": "primary",
      "action_id": "submit_btn"
    }
  ]
}

6. Alert Block

Callout for status, risk, confirmation, or urgency. Currently only supported in modals — do not put alert blocks in messages or Home tabs.

Surfaces: Modals only

{
  "type": "alert",
  "text": {
    "type": "mrkdwn",
    "text": "*Dependency conflict detected* before deploy."
  },
  "level": "warning"
}

7. Card Block

Compact, scannable preview for entities, records, summaries, or agent results.

Surfaces: Messages, Modals, Home tabs

At least one of hero_image, title, actions, or body is required. There is currently no size attribute. For the Slack icon object ({ "type": "icon", "name": "rocket" }), see COMPOSITION.md.

{
  "type": "card",
  "icon": {
    "type": "image",
    "image_url": "https://example.com/icon.png",
    "alt_text": "Icon"
  },
  "title": {
    "type": "mrkdwn",
    "text": "Daily Standup Reminder"
  },
  "subtitle": {
    "type": "mrkdwn",
    "text": "Runs every weekday at *9:00 AM*"
  },
  "body": {
    "type": "mrkdwn",
    "text": "Last run: Today at 9:00 AM. Status: Success"
  },
  "actions": [
    {
      "type": "button",
      "text": { "type": "plain_text", "text": "View Logs" },
      "action_id": "view_logs"
    }
  ]
}

8. Carousel Block

Horizontal group of cards for options, recommendations, search results, or next steps.

Surfaces: Messages, Home tabs

{
  "type": "carousel",
  "elements": [
    { "type": "card", "title": { "type": "mrkdwn", "text": "Option A" } },
    { "type": "card", "title": { "type": "mrkdwn", "text": "Option B" } }
  ]
}

9. Container Block

Groups related blocks under a title, optionally collapsible. Useful for record previews, bulk-update summaries, and grouped content.

Supported child blocks: actions, context, divider, file, header, image, input, rich_text, section, table, video. Containers cannot nest containers, cards, or AI blocks (plan, task_card).

{
  "type": "container",
  "title": { "type": "plain_text", "text": "Bulk update: 2 records selected" },
  "subtitle": { "type": "plain_text", "text": "Review changes before confirming" },
  "is_collapsible": true,
  "child_blocks": [
    { "type": "section", "text": { "type": "mrkdwn", "text": "*DCW-1024*\nStatus: Open → Closed" } },
    { "type": "divider" },
    {
      "type": "actions",
      "elements": [
        {
          "type": "button",
          "text": { "type": "plain_text", "text": "Confirm All" },
          "style": "primary",
          "action_id": "bulk_confirm"
        }
      ]
    }
  ]
}

10. Image Block

Standalone image.

Surfaces: Messages, Modals, Home tabs

Formats: png, jpg, jpeg, gif

{
  "type": "image",
  "image_url": "https://example.com/chart.png",
  "alt_text": "Sales chart Q4 2025",
  "title": { "type": "plain_text", "text": "Q4 Sales" }
}

Using Slack file:

{
  "type": "image",
  "slack_file": { "id": "F0123ABC" },
  "alt_text": "Uploaded screenshot"
}

11. Rich Text Block

Formatted text with nested structure. See RICH-TEXT.md for deep dive.

Surfaces: Messages, Modals, Home tabs

12. Table Block

Basic static tabular data display. For pagination, sorting, filtering, and clickable cells, use the data table block instead.

Surfaces: Messages, Home tabs. For messages, publish as a top-level table in blocks or attachments.

There is no columns property. A static table does not have a dedicated header-row schema; style label cells explicitly when you want a visual header. (The first row is a semantic header only for data_table.)

Row structure: Each row is a flat array of cell objects — NOT an object with a cells property.

Cell types: { "type": "raw_text", "text": "..." } for plain text, { "type": "raw_number", "value": 42, "text": "42" } for numeric values, or { "type": "rich_text", "elements": [...] } for formatted content (links, mentions, emoji, bold).

Column settings: align (left/center/right, default left), is_wrapped (boolean, default false).

Character limits: A single table's character count across all cells cannot exceed 10,000 characters, and the aggregate character count across all table cells in a single message also cannot exceed 10,000. Break large tables into separate messages.

{
  "type": "table",
  "rows": [
    [
      { "type": "raw_text", "text": "Service" },
      { "type": "raw_text", "text": "Status" },
      { "type": "raw_text", "text": "Latency" }
    ],
    [
      { "type": "raw_text", "text": "API" },
      { "type": "raw_text", "text": "Healthy" },
      { "type": "raw_text", "text": "12ms" }
    ],
    [
      { "type": "raw_text", "text": "Worker" },
      { "type": "raw_text", "text": "Degraded" },
      { "type": "raw_text", "text": "340ms" }
    ]
  ],
  "column_settings": [
    { "align": "left" },
    { "align": "center" },
    { "align": "right", "is_wrapped": true }
  ]
}

13. Data Table Block

Rich table with pagination, sorting, filtering, and interactivity (clickable links in cells, Work Object flexpanes).

Surfaces: Messages, Home tabs

Cell types: raw_text, raw_number ({ "type": "raw_number", "value": 42, "text": "42" }), rich_text. Header row cells cannot be rich_text.

Sorting: Alphabetical by default; numeric when every cell in a column is raw_number.

Character limits: 20,000 chars per data table and 20,000 aggregate across all data-table cells per message. This is intentionally double the static table limit.

{
  "type": "data_table",
  "caption": "Department badge levels",
  "rows": [
    [
      { "type": "raw_text", "text": "Name" },
      { "type": "raw_text", "text": "Department" },
      { "type": "raw_text", "text": "Badge" }
    ],
    [
      { "type": "raw_text", "text": "Data Refinement" },
      { "type": "raw_text", "text": "MDR" },
      {
        "type": "rich_text",
        "elements": [
          {
            "type": "rich_text_section",
            "elements": [{ "type": "text", "text": "Blue", "style": { "bold": true } }]
          }
        ]
      }
    ]
  ]
}

14. Data Visualization Block

Renders pie, bar, area, or line charts natively in Slack.

Maximum 2 data visualization blocks per message.

Surfaces: Messages

Pie charts require segments (1–12): each { "label": "...", "value": n } with label ≤20 chars and value > 0. Rendered percentage = value / sum of all segment values.

Bar, area, and line charts require:

• series (1–12 data series): each { "name": "...", "data": [...] }. Name ≤20 chars, unique within the chart. data is 1–20 points of { "label": "...", "value": n } (label ≤20 chars; negative values permitted). Area series layer in array order (first at back); bar series group by label.
• axis_config: { "categories": [...], "x_label": "...", "y_label": "..." }. categories (required) defines valid x-axis labels and their left-to-right order; labels ≤20 chars. x_label/y_label optional, ≤50 chars.

Runtime validation rules:

• Every data_point.label in every series must match a value in axis_config.categories
• Series cannot omit data points — exactly one entry per category
• Series names must be unique within a chart

{
  "type": "data_visualization",
  "title": "Daily Active Users",
  "chart": {
    "type": "line",
    "series": [
      {
        "name": "Free Tier",
        "data": [
          { "label": "Mon", "value": 12000 },
          { "label": "Tue", "value": 13500 },
          { "label": "Wed", "value": 15200 }
        ]
      }
    ],
    "axis_config": {
      "categories": ["Mon", "Tue", "Wed"],
      "x_label": "Day",
      "y_label": "Users"
    }
  }
}

Pie example:

{
  "type": "data_visualization",
  "title": "Ticket Sources",
  "chart": {
    "type": "pie",
    "segments": [
      { "label": "Email", "value": 45 },
      { "label": "Chat", "value": 28 },
      { "label": "Phone", "value": 18 }
    ]
  }
}

15. Markdown Block

Standard Markdown rendering, designed for AI app output.

Surfaces: Messages only

Supports: bold, italic, strikethrough, links, headers, ordered/unordered lists, inline code, code blocks with optional syntax highlighting, block quotes, horizontal rules/dividers, tables, task lists, images (rendered as hyperlink text), and character escaping.

Header rollout note: the current markdown-block reference says every header level renders at the same size, but Slack's March 6, 2026 changelog says variable-sized headers are being rolled out. Use semantic levels and expect client/workspace variation while the reference and rollout converge.

Note: A single markdown block may translate into multiple Slack blocks after rendering.

Escaping: Use backslash to render special characters literally. Supported: \, `, *, _, {, }, [, ], (, ), #, +, -, ., !, &.

{ "type": "markdown", "text": "## Status Report\n\n**API** is healthy.\n\n- Latency: 12ms\n- Error rate: 0.01%" }

16. Context Actions Block

Message-level feedback and action buttons.

Surfaces: Messages only

Compatible elements: feedback_buttons, icon_button

{
  "type": "context_actions",
  "elements": [
    {
      "type": "feedback_buttons",
      "action_id": "feedback_1",
      "positive_button": {
        "text": { "type": "plain_text", "text": "Helpful" },
        "value": "positive"
      },
      "negative_button": {
        "text": { "type": "plain_text", "text": "Not helpful" },
        "value": "negative"
      }
    },
    {
      "type": "icon_button",
      "icon": "trash",
      "text": { "type": "plain_text", "text": "Delete" },
      "action_id": "delete_msg",
      "value": "delete"
    }
  ]
}

17. Input Block

Collects user data via form elements.

Surfaces: Modals, Messages, Home tabs

Compatible elements: plain_text_input, number_input, email_text_input, url_text_input, rich_text_input, static_select, external_select, users_select, conversations_select, channels_select, multi_static_select, multi_external_select, multi_users_select, multi_conversations_select, multi_channels_select, datepicker, datetimepicker, timepicker, checkboxes, radio_buttons, file_input.

18. Video Block

Embedded video player.

Surfaces: Messages, Modals, Home tabs

Requirements: links.embed:write scope, iFrame-embeddable, publicly accessible, cannot point to Slack domains.

19. File Block

Remote file reference. Read-only — appears when retrieving messages containing remote files.

Surfaces: Messages only

Cannot be directly added to messages by apps. Shows up when retrieving messages with remote files.

{ "type": "file", "external_id": "ABCD1", "source": "remote" }

20. Plan Block

Container for displaying sequential tasks or workflow steps, designed for AI agent output.

Surfaces: Messages

{
  "type": "plan",
  "title": "Thinking completed",
  "tasks": [
    {
      "task_id": "call_001",
      "title": "Fetched user profile",
      "status": "complete"
    },
    {
      "task_id": "call_002",
      "title": "Generating report",
      "status": "in_progress",
      "details": {
        "type": "rich_text",
        "elements": [{ "type": "rich_text_section", "elements": [{ "type": "text", "text": "Processing data..." }] }]
      }
    }
  ]
}

21. Task Card Block

Displays a single task with title, status, optional details/output, and source URLs. Used standalone or inside a plan block.

Surfaces: Messages

{
  "type": "task_card",
  "task_id": "task_1",
  "title": "Fetching weather data",
  "status": "complete",
  "output": {
    "type": "rich_text",
    "elements": [
      { "type": "rich_text_section", "elements": [{ "type": "text", "text": "Found weather data from 2 sources" }] }
    ]
  },
  "sources": [
    { "type": "url", "url": "https://weather.com/", "text": "weather.com" },
    { "type": "url", "url": "https://accuweather.com/", "text": "accuweather.com" }
  ]
}