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Reference: Layout 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.

The lists of fields and values below describe the JSON that apps can use to generate each block:

Block type Available in surfaces
Actions Modals Messages Home tabs
Context Modals Messages Home tabs
Divider Modals Messages Home tabs
File Messages
Header Modals Messages Home tabs
Image Modals Messages Home tabs
Input Modals Messages Home tabs
Section Modals Messages Home tabs

Actions Block

Available in surfaces: Modals Messages Home tabs

A block that is used to hold interactive elements.

An action block containing multiple interactive elements

Fields

Field Type Required? Description
type String Yes The type of block. For an actions block, type is always actions.
elements Object[] Yes An array of interactive element objects - buttons, select menus, overflow menus, or date pickers. There is a maximum of 5 elements in each action block.
block_id String No A string acting as 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.

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"
    }
  ]
}

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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"
    }
  ]
}

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Context Block

Available in surfaces: Modals Messages Home tabs

Displays message context, which can include both images and text.

An example of a context block

Fields

Field Type Required? Description
type String Yes The type of block. For a context block, type is always context.
elements Object[] Yes An array of image elements and text objects. Maximum number of items is 10.
block_id String No A string acting as 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.

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**"
    }
  ]
}

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Divider Block

Available in surfaces: Modals Messages Home tabs

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.

An example of a divider block

Fields

Field Type Required? Description
type String Yes The type of block. For a divider block, type is always divider.
block_id String No A string acting as 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.

Example 

{
  "type": "divider"
}

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File Block

Appears in surfaces: Messages

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.

Fields

Field Type Required? Description
type String Yes The type of block. For a file block, type is always file.
external_id String Yes The external unique ID for this file.
source String Yes At the moment, source will always be remote for a remote file.
block_id String No A string acting as 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.

Example 

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

Available in surfaces: Modals Messages Home tabs

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.

An example of a header block

Fields

Field Type Required? Description
type String Yes The type of block. For this block, type will always be header.
text Object Yes 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.
block_id String No A string acting as 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.

Examples

A header block:

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

View an example

Image Block

Available in surfaces: Modals Messages Home tabs

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

An example of an image block

Fields

Field Type Required? Description
type String Yes The type of block. For an image block, type is always image.
image_url String Yes The URL of the image to be displayed. Maximum length for this field is 3000 characters.
alt_text String Yes A plain-text summary of the image. This should not contain any markup. Maximum length for this field is 2000 characters.
title Object No 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.
block_id String No A string acting as 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.

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."
}

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Input block

Available in surfaces: Modals Messages Home tabs

A block that collects information from users - it can hold a plain-text input element, a checkbox element, a radio button element, a select menu element, a multi-select menu element, or a datepicker.

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

An example of an input block

Fields

Field Type Required? Description
type String Yes The type of block. For an input block, type is always input.
label Object Yes 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.
element Object Yes An plain-text input element, a checkbox element, a radio button element, a select menu element, a multi-select menu element, or a datepicker.
dispatch_action Boolean No A boolean that indicates whether or not the use of elements in this block should dispatch a block_actions payload. Defaults to false.
block_id String No A string acting as 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.
hint Object No 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.
optional Boolean No A boolean that indicates whether the input element may be empty when a user submits the modal. Defaults to false.

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
  }
}

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Section Block

Available in surfaces: Modals Messages Home tabs

A section is one of the most flexible blocks available - it can be used as a simple text block, in combination with text fields, or side-by-side with any of the available block elements.

An example of a section block

Fields

Field Type Required? Description
type String Yes The type of block. For a section block, type will always be section.
text Object Preferred The text for the block, in the form of a text object. Maximum length for the text in this field is 3000 characters. This field is not required if a valid array of fields objects is provided instead.
block_id String No A string acting as 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.
fields Object[] Maybe 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.
accessory Object No One of the available element objects.

Examples

A simple text section block:

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

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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"
    }
  ]
}

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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"
    }
  }
}

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