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
Section	Modals Messages Home tabs

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Actions Block

Available in surfaces: Modals Messages Home tabs

A block that is used to hold 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"
    }
  ]
}

View this block

---

Context Block

Available in surfaces: Modals Messages Home tabs

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

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**"
    }
  ]
}

View this block

---

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.

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"
}

View this block

---

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",
}

---

Header Block

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.

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 3000 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.

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."
}

View this block

---

Input block

Available in surfaces: Modals

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

Read our guide to using modals to learn how input blocks pass information to your app.

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 select menu element, a multi-select menu element, or a datepicker.
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.
hint	Object	No	An optional hint that appears below an input element in a lighter grey. It must be a 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
  }
}

View this block

---

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.

Fields

Field	Type	Required?	Description
type	String	Yes	The type of block. For a section block, type will always be section.
text	Object	Yes	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[]	No	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_."
  }
}

View this block

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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