Reference: blocks

Blocks are a series of components that can be combined to create visually rich and compellingly interactive messages.

Read our guide to building block layouts to learn where and how to use each of these components. You can include up to 50 blocks in each message, and 100 blocks in modals or Home tabs.

This page lists the JSON payloads that your app can use to generate each block. Select the block you'd like to build:

Blocks

Block type Available in surfaces Compatible block elements
Actions block Modals Messages Home tabs Many. See below.
Context block Modals Messages Home tabs Image
Divider block Modals Messages Home tabs None.
File block Messages None.
Header block Modals Messages Home tabs None.
Image block Modals Messages Home tabs None.
Input block Modals Messages Home tabs Many. See below.
Rich text block Modals Messages Home tabs None.
Section block Modals Messages Home tabs Many. See below.
Video block Modals Messages Home tabs None.

Actions block

Holds multiple interactive elements.

Available in surfaces Compatible block elements
Modals Messages Home tabs Button Checkboxes Date picker Datetime picker Multi-select menus Overflow menu Radio button Select menu Time Picker Workflow buttons

Example:

An action block containing multiple interactive elements

Fields

Field Type Description Required?
type String The type of block. For an actions block, type is always actions. Yes
elements Object[] An array of interactive element objects - buttons, select menus, overflow menus, or date pickers. There is a maximum of 25 elements in each action block. Yes
block_id String A unique identifier for a block. If not specified, a block_id will be generated. You can use this block_id when you receive an interaction payload to identify the source of the action. Maximum length for this field is 255 characters. block_id should be unique for each message and each iteration of a message. If a message is updated, use a new block_id. No

Examples

An actions block with a select menu and a button:

{
  "type": "actions",
  "block_id": "actions1",
  "elements": [
    {
      "type": "static_select",
      "placeholder":{
          "type": "plain_text",
          "text": "Which witch is the witchiest witch?"
      },
      "action_id": "select_2",
      "options": [
        {
          "text": {
              "type": "plain_text",
              "text": "Matilda"
          },
          "value": "matilda"
        },
        {
          "text": {
              "type": "plain_text",
              "text": "Glinda"
          },
          "value": "glinda"
        },
        {
          "text": {
              "type": "plain_text",
              "text": "Granny Weatherwax"
          },
          "value": "grannyWeatherwax"
        },
        {
          "text": {
              "type": "plain_text",
              "text": "Hermione"
          },
          "value": "hermione"
        }
      ]
    },
    {
      "type": "button",
      "text": {
          "type": "plain_text",
          "text": "Cancel"
      },
      "value": "cancel",
      "action_id": "button_1"
    }
  ]
}

View this block in Block Kit Builder

An actions block with a datepicker, an overflow, and a button:

{
  "type": "actions",
  "block_id": "actionblock789",
  "elements": [
    {
      "type": "datepicker",
      "action_id": "datepicker123",
      "initial_date": "1990-04-28",
      "placeholder": {
        "type": "plain_text",
        "text": "Select a date"
      }
    },
    {
      "type": "overflow",
      "options": [
        {
          "text": {
            "type": "plain_text",
            "text": "*this is plain_text text*"
          },
          "value": "value-0"
        },
        {
          "text": {
            "type": "plain_text",
            "text": "*this is plain_text text*"
          },
          "value": "value-1"
        },
        {
          "text": {
            "type": "plain_text",
            "text": "*this is plain_text text*"
          },
          "value": "value-2"
        },
        {
          "text": {
            "type": "plain_text",
            "text": "*this is plain_text text*"
          },
          "value": "value-3"
        },
        {
          "text": {
            "type": "plain_text",
            "text": "*this is plain_text text*"
          },
          "value": "value-4"
        }
      ],
      "action_id": "overflow"
    },
    {
      "type": "button",
      "text": {
        "type": "plain_text",
        "text": "Click Me"
      },
      "value": "click_me_123",
      "action_id": "button"
    }
  ]
}

View this block in Block Kit Builder

Context block

Displays contextual info, which can include both images and text.

Available in surfaces Compatible block elements
Modals Messages Home tabs Image

Example:

An example of a context block

Fields

Field Type Description Required?
type String The type of block. For a context block, type is always context. Yes
elements Object[] An array of image elements and text objects. Maximum number of items is 10. Yes
block_id String A unique identifier for a block. If not specified, one will be generated. Maximum length for this field is 255 characters. block_id should be unique for each message and each iteration of a message. If a message is updated, use a new block_id. No

Example

{
  "type": "context",
  "elements": [
    {
      "type": "image",
      "image_url": "https://image.freepik.com/free-photo/red-drawing-pin_1156-445.jpg",
      "alt_text": "images"
    },
    {
      "type": "mrkdwn",
      "text": "Location: **Dogpatch**"
    }
  ]
}

View this block in Block Kit Builder

Divider block

Visually separates pieces of info inside of a message.

A content divider, like an <hr>, to split up different blocks inside of a message. The divider block is nice and neat, requiring only a type.

Available in surfaces Compatible block elements
Modals Messages Home tabs None

Example:

An example of a divider block

Fields

Field Type Description Required?
type String The type of block. For a divider block, type is always divider. Yes
block_id String A unique identifier for a block. If not specified, one will be generated. Maximum length for this field is 255 characters. block_id should be unique for each message and each iteration of a message. If a message is updated, use a new block_id. No

Example

{
  "type": "divider"
}

View this block in Block Kit Builder

File block

Displays a remote file.

You can't add this block to app surfaces directly, but it will show up when retrieving messages that contain remote files.

If you want to add remote files to messages, follow our guide.

Available in surfaces Compatible block elements
Messages None

Fields

Field Type Description Required?
type String The type of block. For a file block, type is always file. Yes
external_id String The external unique ID for this file. Yes
source String At the moment, source will always be remote for a remote file. Yes
block_id String A unique identifier for a block. If not specified, one will be generated. Maximum length for this field is 255 characters. block_id should be unique for each message and each iteration of a message. If a message is updated, use a new block_id. No

Example

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

Displays a larger-sized text block.

A header is a plain-text block that displays in a larger, bold font. Use it to delineate between different groups of content in your app's surfaces.

Available in surfaces Compatible block elements
Modals Messages Home tabs None

Example:

An example of a header block

Fields

Field Type Description Required?
type String The type of block. For this block, type will always be header. Yes
text Object The text for the block, in the form of a plain_text text object. Maximum length for the text in this field is 150 characters. Yes
block_id String A unique identifier for a block. If not specified, one will be generated. Maximum length for this field is 255 characters. block_id should be unique for each message and each iteration of a message. If a message is updated, use a new block_id. No

Examples

A header block:

{
  "type": "header",
  "text": {
    "type": "plain_text",
    "text": "Budget Performance"
  }
}

View this block in Block Kit Builder

Image block

Displays an image.

An image block, designed to make those cat photos really pop.

Available in surfaces Compatible block elements
Modals Messages Home tabs None

Example:

An example of an image block

Fields

Field Type Description Required?
type String The type of block. For an image block, type is always image. Yes
image_url String The URL of the image to be displayed. Maximum length for this field is 3000 characters. Yes
alt_text String A plain-text summary of the image. This should not contain any markup. Maximum length for this field is 2000 characters. Yes
title Object An optional title for the image in the form of a text object that can only be of type: plain_text. Maximum length for the text in this field is 2000 characters. No
block_id String A unique identifier for a block. If not specified, one will be generated. Maximum length for this field is 255 characters. block_id should be unique for each message and each iteration of a message. If a message is updated, use a new block_id. No

Example

{
  "type": "image",
  "title": {
    "type": "plain_text",
    "text": "Please enjoy this photo of a kitten"
  },
  "block_id": "image4",
  "image_url": "http://placekitten.com/500/500",
  "alt_text": "An incredibly cute kitten."
}

View this block in Block Kit Builder

Input block

Collects information from users via block elements.

Read our guides to collecting input in modals or in Home tabs to learn how input blocks pass information to your app.

Available in surfaces Compatible block elements
Modals Messages Home tabs Checkboxes Date picker Datetime picker Email input File input Multi-select menus Number input Plain-text input Radio button Select menu Time Picker URL input

Example:

An example of an input block

Fields

Field Type Description Required?
type String The type of block. For an input block, type is always input. Yes
label Object A label that appears above an input element in the form of a text object that must have type of plain_text. Maximum length for the text in this field is 2000 characters. Yes
element Object A block element. See above for full list. Yes
dispatch_action Boolean A boolean that indicates whether or not the use of elements in this block should dispatch a block_actions payload. Defaults to false. No
block_id String A unique identifier for a block. If not specified, one will be generated. Maximum length for this field is 255 characters. block_id should be unique for each message or view and each iteration of a message or view. If a message or view is updated, use a new block_id. No
hint Object An optional hint that appears below an input element in a lighter grey. It must be a text object with a type of plain_text. Maximum length for the text in this field is 2000 characters. No
optional Boolean A boolean that indicates whether the input element may be empty when a user submits the modal. Defaults to false. No

Example

An input block containing a plain-text input element.

{
  "type": "input",
  "element": {
    "type": "plain_text_input"
  },
  "label": {
    "type": "plain_text",
    "text": "Label",
    "emoji": true
  }
}

View this block in Block Kit Builder

Rich text block

Displays formated, structured representation of text.

It is also the output of the Slack client's WYSIWYG composer, so all messages sent by end-users will have this format. Use this block to include user-defined formatted text in your Block Kit payload.

You might encounter a rich_text block in a message payload, as a built-in type in the next-generation Slack platform, or as output of the rich_text_input block element.

Available in surfaces Compatible block elements
Modals Messages Home tabs None

Fields

Field Type Description Required?
type String The type of block. For a rich text block, type is always rich_text. Yes
elements Object[] An array of rich text objects - rich_text_section, rich_text_list, rich_text_quote, rich_text_preformatted Yes
block_id String A unique identifier for a block. If not specified, one will be generated. Maximum length for this field is 255 characters. block_id should be unique for each message or view and each iteration of a message or view. If a message or view is updated, use a new block_id. No

An example of a rich text block

Example

A rich text block:

"type": "rich_text",
  "elements": [
    {
      "type": "rich_text_section",
      "elements": [
        {
          "type": "text",
          "text": "Hello there, I am a basic rich text block!"
        }
      ]
    }
  ]
},
{
  "type": "rich_text",
  "elements": [
    {
      "type": "rich_text_section",
      "elements": [
        {
          "type": "text",
          "text": "Hello there, "
        },
        {
          "type": "text",
          "text": "I am a bold rich text block!",
          "style": {
            "bold": true
          }
        }
      ]
    }
  ]
},
{
  "type": "rich_text",
  "elements": [
    {
      "type": "rich_text_section",
      "elements": [
        {
          "type": "text",
          "text": "Hello there, "
        },
        {
          "type": "text",
          "text": "I am an italic rich text block!",
          "style": {
            "italic": true
          }
        }
      ]
    }
  ]
},
{
  "type": "rich_text",
  "elements": [
    {
      "type": "rich_text_section",
      "elements": [
        {
          "type": "text",
          "text": "Hello there, "
        },
        {
          "type": "text",
          "text": "I am a strikethrough rich text block!",
          "style": {
            "strike": true
          }
        }
      ]
    }
  ]
}

View this block

Section block

Displays text, possibly alongside block elements.

A section can be used as a text block, in combination with text fields, or side-by-side with certain block elements.

Available in Surfaces Compatible block elements
Modals Messages Home tabs Button Checkboxes Date picker Image Multi-select menus Overflow menu Radio button Select menu Time Picker Workflow buttons

Example:

An example of a section block

Fields

Field Type Description Required?
type String The type of block. For a section block, type will always be section. Yes
text Object The text for the block, in the form of a text object. Minimum length for the text in this field is 1 and maximum length is 3000 characters. This field is not required if a valid array of fields objects is provided instead. Preferred
block_id String A unique identifier for a block. If not specified, one will be generated. You can use this block_id when you receive an interaction payload to identify the source of the action. Maximum length for this field is 255 characters. block_id should be unique for each message and each iteration of a message. If a message is updated, use a new block_id. No
fields Object[] Required if no text is provided. An array of text objects. Any text objects included with fields will be rendered in a compact format that allows for 2 columns of side-by-side text. Maximum number of items is 10. Maximum length for the text in each item is 2000 characters. Click here for an example. Maybe
accessory Object One of the compatible element objects. Be sure to confirm the desired element works with section. No

Examples

A text section block:

{
  "type": "section",
  "text": {
    "type": "mrkdwn",
    "text": "A message *with some bold text* and _some italicized text_."
  }
}

View this block in Block Kit Builder

A section block containing text fields:

{
  "type": "section",
  "text": {
    "text": "A message *with some bold text* and _some italicized text_.",
    "type": "mrkdwn"
  },
  "fields": [
    {
      "type": "mrkdwn",
      "text": "High"
    },
    {
      "type": "plain_text",
      "emoji": true,
      "text": "String"
    }
  ]
}

View this block in Block Kit Builder

A section block containing a datepicker element:

{
  "type": "section",
  "text": {
    "text": "*Sally* has requested you set the deadline for the Nano launch project",
    "type": "mrkdwn"
  },
  "accessory": {
    "type": "datepicker",
    "action_id": "datepicker123",
    "initial_date": "1990-04-28",
    "placeholder": {
      "type": "plain_text",
      "text": "Select a date"
    }
  }
}

View this block in Block Kit Builder

Video block

Displays an embedded video player.

A video block is designed to embed videos in all app surfaces (e.g. link unfurls, messages, modals, App Home) β€” anywhere you can put blocks! To use the video block within your app, you must have the links.embed:write scope.

The metadata received in the block payload will be used to construct the description, provider, and title of the video in all clients. Developers have the flexibility to leave non-mandatory fields null and use other blocks to format this content.

Requirements

  • Video blocks can only be posted by apps; users are not allowed to post embedded videos directly from Block Kit Builder.
  • Your app must have the the links.embed:write scope for both user and bot tokens.
  • video_url has to be included in the unfurl domains specified in your app.
  • video_url should be publicly accessible, unless the app relies on information received from the Events API payloads to make a decision on whether the viewer(s) of the content should have access. If so, the service could create a unique URL accessible only via Slack.
  • video_url must be compatible with an embeddable iFrame.
  • video_url must return a 2xx code OR 3xx with less than 5 redirects and an eventual 2xx.
  • video_url must not point to any Slack-related domain.

Constraints

  • Embeddable video players only (audio-only permitted)
  • Navigation, scrolling and overlays are not allowed within the iFrame.
  • Interactivity (e.g. likes, comments, and reactions) are allowed within your player but shouldn't completely overlay or navigate away from the content being embedded. These interactions will be anonymous since no user data is transferred to the embedded view.
Available in surfaces Compatible block elements
Modals Messages Home tabs None

Example:

An example of a video block for web

Fields

Property Type Description Required?
type string The type of block. For a video block, type will always be video. Yes
alt_text string A tooltip for the video. Required for accessibility Yes
author_name string Author name to be displayed. Must be less than 50 characters. No
block_id string A unique identifier for a block. If not specified, one will be generated. Maximum length for this field is 255 characters. block_id should be unique for each message and each iteration of a message. If a message is updated, use a new block_id. No
description Object Description for video in the form of a text object that must have type of plain_text. text within must be less than 200 characters. Preferred
provider_icon_url string Icon for the video provider, e.g. YouTube icon. No
provider_name string The originating application or domain of the video, e.g. YouTube. No
title Object Video title in the form of a text object that must have type of plain_text. text within must be less than 200 characters. Yes
title_url string Hyperlink for the title text. Must correspond to the non-embeddable URL for the video. Must go to an HTTPS URL. Preferred
thumbnail_url string The thumbnail image URL Yes
video_url string The URL to be embedded. Must match any existing unfurl domains within the app and point to a HTTPS URL. Yes

Examples

An example video block payload:

{
  "blocks": [
    {
      "type": "section",
      "text": {
        "type": "plain_text",
        "text": "I think it's super cool",
        "emoji": true
      }
    },
    {
      "type": "video",
      "title": {
        "type": "plain_text",
        "text": "How to use Slack.",
        "emoji": true
      },
      "title_url": "https://www.youtube.com/watch?v=RRxQQxiM7AA",
      "description": {
        "type": "plain_text",
        "text": "Slack is a nifty way to communicate with your team.",
        "emoji": true
      },
      "video_url": "https://www.youtube.com/embed/RRxQQxiM7AA?feature=oembed&autoplay=1",
      "alt_text": "How to use Slack?",
      "thumbnail_url": "https://i.ytimg.com/vi/RRxQQxiM7AA/hqdefault.jpg",
      "author_name": "Arcado Buendia",
      "provider_name": "YouTube",
      "provider_icon_url": "https://a.slack-edge.com/80588/img/unfurl_icons/youtube.png"
    }
  ]
}