Block Elements — Complete Property Reference

Sources:

Block Kit Elements — Slack

Current interactive and display element types with properties, constraints, and compatible blocks. Rich-text structural and inline elements are documented separately in RICH-TEXT.md.

Current compatibility matrix

Element family	Blocks	Surfaces
button	section, actions	messages, modals, Home tabs
overflow	section, actions	messages, modals, Home tabs
single/multi selects	section, actions, input	messages, modals, Home tabs
datepicker, timepicker	section, actions, input	messages, modals, Home tabs
datetimepicker	actions, input	messages, modals
checkboxes, radio_buttons	section, actions, input	messages, modals, Home tabs
plain_text_input	input	messages, modals, Home tabs
number_input, email_text_input, url_text_input, file_input	input	modals only
rich_text_input	input	modals, Home tabs
feedback_buttons, icon_button	context_actions	messages only
image	section, context	messages, modals, Home tabs
workflow_button	section, actions	messages only
URL source	task_card `sources`	messages only

card.actions also accepts up to three button-shaped objects, but the standard button element's live compatibility facts list section and actions blocks.

Button
Overflow Menu
Select Menus (5 types)
Multi-Select Menus (5 types)
Date Picker
Time Picker
Datetime Picker
Checkboxes
Radio Buttons
Plain Text Input
Number Input
Email Input
URL Input
Rich Text Input
File Input
Feedback Buttons
Icon Button
Image Element
Workflow Button
URL Source Element

Button

Property	Type	Required	Constraints
`type`	string	Yes	`"button"`
`text`	text object	Yes	`plain_text` only, max 75 chars (displays ~30)
`action_id`	string	No	Max 255 chars
`url`	string	No	Max 3000 chars, opens in browser
`value`	string	No	Max 2000 chars, sent in payload
`style`	string	No	`"primary"` (green) or `"danger"` (red)
`confirm`	confirm object	No	Confirmation dialog
`accessibility_label`	string	No	Screen reader text, max 75 chars

Blocks: section (accessory), actions. Card blocks separately accept button objects in card.actions.

Overflow Menu

Property	Type	Required	Constraints
`type`	string	Yes	`"overflow"`
`options`	option[]	Yes	Max 5 options
`action_id`	string	No	Max 255 chars
`confirm`	confirm object	No	Confirmation dialog

Blocks: section (accessory), actions

Select Menus (5 types)

All share: action_id (255 chars), confirm, placeholder (plain_text, 150 chars), and focus_on_load. Only one element in a view may set focus_on_load: true.

Static Select (`static_select`)

options: option[] — max 100. Required unless option_groups provided
option_groups: option group[] — max 100 groups
initial_option: option object — pre-selected

External Select (`external_select`)

min_query_length: integer — chars before typeahead (default 3)
initial_option: option object
Requires Options Load URL configured in app settings

Users Select (`users_select`)

initial_user: string — user ID

Conversations Select (`conversations_select`)

initial_conversation: string — conversation ID
default_to_current_conversation: boolean (default false)
filter: conversation filter object
response_url_enabled: boolean — for modals

Channels Select (`channels_select`)

initial_channel: string — public channel ID
response_url_enabled: boolean — for modals

Blocks: section (accessory), actions, input

Multi-Select Menus (5 types)

All share: action_id (255 chars), confirm, placeholder (150 chars), and max_selected_items (integer, min 1). focus_on_load is documented on static/users/conversations/channels multi-selects, but is not currently listed for multi_external_select.

Multi Static Select (`multi_static_select`)

options: option[] — max 100, each option under 76 chars. Required unless option_groups is provided
option_groups: option group[] — max 100; mutually exclusive with options
initial_options: option[]

Multi External Select (`multi_external_select`)

min_query_length: integer (default 3)
initial_options: option[]

Multi Users Select (`multi_users_select`)

initial_users: string[] — user IDs

Multi Conversations Select (`multi_conversations_select`)

initial_conversations: string[] — conversation IDs
default_to_current_conversation: boolean
filter: conversation filter object

Multi Channels Select (`multi_channels_select`)

initial_channels: string[] — channel IDs

Blocks: section (accessory), actions, input

Date Picker

Property	Type	Required	Constraints
`type`	string	Yes	`"datepicker"`
`action_id`	string	No	Max 255 chars
`initial_date`	string	No	`YYYY-MM-DD` format
`confirm`	confirm object	No
`focus_on_load`	boolean	No	Default false
`placeholder`	text object	No	`plain_text`, max 150 chars

Blocks: section (accessory), actions, input

Time Picker

Property	Type	Required	Constraints
`type`	string	Yes	`"timepicker"`
`action_id`	string	No	Max 255 chars
`initial_time`	string	No	`HH:mm` (24-hour)
`timezone`	string	No	IANA timezone (e.g., `"America/Los_Angeles"`)
`confirm`	confirm object	No
`focus_on_load`	boolean	No	Default false
`placeholder`	text object	No	`plain_text`, max 150 chars

Blocks: section (accessory), actions, input

Datetime Picker

Property	Type	Required	Constraints
`type`	string	Yes	`"datetimepicker"`
`action_id`	string	No	Max 255 chars
`initial_date_time`	integer	No	Unix timestamp
`confirm`	confirm object	No
`focus_on_load`	boolean	No	Default false

Blocks: actions, input. Surfaces: messages and modals.

Checkboxes

Property	Type	Required	Constraints
`type`	string	Yes	`"checkboxes"`
`options`	option[]	Yes	Max 10 options
`action_id`	string	No	Max 255 chars
`initial_options`	option[]	No	Must match items in `options`
`confirm`	confirm object	No
`focus_on_load`	boolean	No	Default false

Blocks: section (accessory), actions, input

Radio Buttons

Property	Type	Required	Constraints
`type`	string	Yes	`"radio_buttons"`
`options`	option[]	Yes	Max 10 options
`action_id`	string	No	Max 255 chars
`initial_option`	option	No	Must match one item in `options`
`confirm`	confirm object	No
`focus_on_load`	boolean	No	Default false

Blocks: section (accessory), actions, input

Plain Text Input

Property	Type	Required	Constraints
`type`	string	Yes	`"plain_text_input"`
`action_id`	string	No	Max 255 chars
`initial_value`	string	No	Pre-populated text
`multiline`	boolean	No	Default false. True = textarea
`min_length`	integer	No	0-3000
`max_length`	integer	No	1-3000
`dispatch_action_config`	object	No	`trigger_actions_on` array
`focus_on_load`	boolean	No	Default false
`placeholder`	text object	No	`plain_text`, max 150 chars
Blocks: input. Surfaces: messages, modals, and Home tabs.

Number Input

Property	Type	Required	Constraints
`type`	string	Yes	`"number_input"`
`is_decimal_allowed`	boolean	Yes	Allow decimal numbers
`action_id`	string	No	Max 255 chars
`initial_value`	string	No	Initial number as string
`min_value`	string	No	Minimum allowed
`max_value`	string	No	Maximum allowed
`dispatch_action_config`	object	No
`focus_on_load`	boolean	No	Default false
`placeholder`	text object	No	`plain_text`, max 150 chars

Blocks: input. Surfaces: modals only.

Email Input

Property	Type	Required	Constraints
`type`	string	Yes	`"email_text_input"`
`action_id`	string	No	Max 255 chars
`initial_value`	string	No	Pre-populated email
`dispatch_action_config`	object	No
`focus_on_load`	boolean	No	Default false
`placeholder`	text object	No	`plain_text`, max 150 chars

Blocks: input. Surfaces: modals only.

URL Input

Property	Type	Required	Constraints
`type`	string	Yes	`"url_text_input"`
`action_id`	string	No	Max 255 chars
`initial_value`	string	No	Pre-populated URL
`dispatch_action_config`	object	No
`focus_on_load`	boolean	No	Default false
`placeholder`	text object	No	`plain_text`, max 150 chars

Blocks: input. Surfaces: modals only.

Rich Text Input

Property	Type	Required	Constraints
`type`	string	Yes	`"rich_text_input"`
`action_id`	string	Yes	Max 255 chars
`initial_value`	rich text object	No	Pre-populated rich text
`dispatch_action_config`	object	No
`focus_on_load`	boolean	No	Default false
`placeholder`	text object	No	`plain_text`, max 150 chars
`min_lines`	integer	No	Visible-line minimum, 1-100
`max_lines`	integer	No	Growth maximum, 1-100; defaults to 8

Blocks: input. Surfaces: modals and Home tabs.

File Input

Property	Type	Required	Constraints
`type`	string	Yes	`"file_input"`
`action_id`	string	No	Max 255 chars
`filetypes`	string[]	No	Allowed extensions (e.g., `["jpg", "png"]`). Client-side only — perform server-side validation too
`max_files`	integer	No	Max uploadable files (1-10, default 10)

Blocks: input. Surfaces: modals only. Note: dispatch_action: true is incompatible with file_input.

Requirements: App must have files:read scope. Max 100MB per file.

Feedback Buttons

Property	Type	Required	Constraints
`type`	string	Yes	`"feedback_buttons"`
`positive_button`	button object	Yes	`text` (plain_text, 75 chars), `value` (2000 chars)
`negative_button`	button object	Yes	Same as positive
`action_id`	string	No	Max 255 chars

Both buttons support accessibility_label (75 chars).

Blocks: context_actions

Icon Button

Property	Type	Required	Constraints
`type`	string	Yes	`"icon_button"`
`icon`	string	Yes	Only `"trash"` available
`text`	text object	Yes	`plain_text` only
`action_id`	string	No	Max 255 chars
`value`	string	No	Max 2000 chars
`confirm`	confirm object	No
`accessibility_label`	string	No	Max 75 chars
`visible_to_user_ids`	string[]	No	Only these users see the button

Blocks: context_actions

Image Element

Property	Type	Required	Constraints
`type`	string	Yes	`"image"`
`alt_text`	string	Yes	Plain-text image summary; the live image-element page states no numeric limit
`image_url`	string	Conditional	Max 3000 chars. Required unless `slack_file`
`slack_file`	object	Conditional	`{ url }` or `{ id }`

Blocks: section (accessory), context (element). Surfaces: messages, modals, and Home tabs.

Workflow Button

Property	Type	Required	Constraints
`type`	string	Yes	`"workflow_button"`
`text`	text object	Yes	`plain_text` only, max 75 chars
`workflow`	workflow object	Yes	Contains trigger URL + input parameters
`action_id`	string	Yes	Max 255 chars, unique within block
`style`	string	No	`"primary"` or `"danger"`
`accessibility_label`	string	No	Max 75 chars

Blocks: section, actions. Surfaces: messages only.

URL Source Element

Property	Type	Required	Constraints
`type`	string	Yes	`"url"`
`url`	string	Yes	Target URL reference
`text`	string	Yes	Display text shown to users

Blocks: task_card (sources array only)

{ "type": "url", "url": "https://docs.slack.dev/", "text": "Slack API docs" }

/slack-block-kit

referencesELEMENTS.md

Block Elements — Complete Property Reference

Current compatibility matrix

Table of Contents

Button

Overflow Menu

Select Menus (5 types)

Static Select (`static_select`)

External Select (`external_select`)

Users Select (`users_select`)

Conversations Select (`conversations_select`)

Channels Select (`channels_select`)

Multi-Select Menus (5 types)

Multi Static Select (`multi_static_select`)

Multi External Select (`multi_external_select`)

Multi Users Select (`multi_users_select`)

Multi Conversations Select (`multi_conversations_select`)

Multi Channels Select (`multi_channels_select`)

Date Picker

Time Picker

Datetime Picker

Checkboxes

Radio Buttons

Plain Text Input

Number Input

Email Input

URL Input

Rich Text Input

File Input

Feedback Buttons

Icon Button

Image Element

Workflow Button

URL Source Element

Third-party checks

Provenance

/slack-block-kit

slack-block-kitreferencesELEMENTS.md

Block Elements — Complete Property Reference

Current compatibility matrix

Table of Contents

Button

Overflow Menu

Select Menus (5 types)

Static Select (static_select)

External Select (external_select)

Users Select (users_select)

Conversations Select (conversations_select)

Channels Select (channels_select)

Multi-Select Menus (5 types)

Multi Static Select (multi_static_select)

Multi External Select (multi_external_select)

Multi Users Select (multi_users_select)

Multi Conversations Select (multi_conversations_select)

Multi Channels Select (multi_channels_select)

Date Picker

Time Picker

Datetime Picker

Checkboxes

Radio Buttons

Plain Text Input

Number Input

Email Input

URL Input

Rich Text Input

File Input

Feedback Buttons

Icon Button

Image Element

Workflow Button

URL Source Element

Third-party checks

Provenance

README badge

Related skills

referencesELEMENTS.md

Static Select (`static_select`)

External Select (`external_select`)

Users Select (`users_select`)

Conversations Select (`conversations_select`)

Channels Select (`channels_select`)

Multi Static Select (`multi_static_select`)

Multi External Select (`multi_external_select`)

Multi Users Select (`multi_users_select`)

Multi Conversations Select (`multi_conversations_select`)

Multi Channels Select (`multi_channels_select`)