Blocks

This page documents the public C# API for blocks, generated from the XML documentation of the compiled library. Values are immutable, constructors take named arguments and validate them, and read-only properties return what was passed.

Every block implements IBlock, so blocks of any kind share one collection type, and values serialize as Slack JSON with ToJson() or System.Text.Json.

ActionsBlock

A block that holds interactive elements such as buttons and menus.

• Required: elements.

See the Slack reference.

Implements IBlock.

ActionsBlock

Creates and validates a ActionsBlock.

public ActionsBlock(IEnumerable<IElement> elements, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
elements	Interactive elements in display order. Required. Slack allows at most 25 items.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: ActionsBlock, IElement

Elements

Gets interactive elements in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<IElement> Elements { get; }

Related types: IElement

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

AlertBlock

A severity-labelled alert, available in modals.

• Required: text.

See the Slack reference.

Implements IBlock.

AlertBlock

Creates and validates a AlertBlock.

public AlertBlock(Text text, AlertLevel? level = null, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
text	The alert message. Required. Slack allows at most 200 characters. A string is sent as a mrkdwn text object.
level	The alert severity, which controls its color and icon.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: AlertBlock, AlertLevel, Text

Text

Gets the alert message.

public Text Text { get; }

Related types: Text

Level

Gets the alert severity, which controls its color and icon.

The value, or null when it was not set.

public AlertLevel? Level { get; }

Related types: AlertLevel

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

AlertLevel

Severity levels supported by alert blocks.

ToWireValue() returns the value Slack expects in JSON.

Constant	Slack value	Meaning
Default	default	Neutral styling.
Info	info	Informational styling.
Warning	warning	Warning styling.
Error	error	Error styling.
Success	success	Success styling.

CardBlock

A compact card with an image, text, and up to three buttons.

• Provide at least one of a hero image, title, actions, or body.
• An image icon and a Slack icon cannot be combined.

See the Slack reference.

Implements IBlock.

CardBlock

Creates and validates a CardBlock.

public CardBlock(ImageElement? heroImage = null, ImageElement? icon = null, Text? title = null, Text? subtitle = null, Text? body = null, IEnumerable<ButtonElement>? actions = null, SlackIcon? slackIcon = null, Text? subtext = null, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
heroImage	The image displayed prominently at the top of the card.
icon	The image displayed beside the title.
title	The card title. Slack allows at most 150 characters. A string is sent as a mrkdwn text object.
subtitle	The supporting text shown below the title. Slack allows at most 150 characters. A string is sent as a mrkdwn text object.
body	The main body text of the card. Slack allows at most 200 characters. A string is sent as a mrkdwn text object.
actions	Buttons displayed at the bottom of the card, in display order. Slack allows at most 3 items.
slackIcon	A Slack-provided icon displayed beside the title. Cannot be combined with an image icon.
subtext	The small print shown at the bottom of the card. Slack allows at most 200 characters. A string is sent as a mrkdwn text object.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: ButtonElement, CardBlock, ImageElement, SlackIcon, Text

HeroImage

Gets the image displayed prominently at the top of the card.

The value, or null when it was not set.

public ImageElement? HeroImage { get; }

Related types: ImageElement

Icon

Gets the image displayed beside the title.

The value, or null when it was not set.

public ImageElement? Icon { get; }

Related types: ImageElement

Title

Gets the card title.

The value, or null when it was not set.

public Text? Title { get; }

Related types: Text

Subtitle

Gets the supporting text shown below the title.

The value, or null when it was not set.

public Text? Subtitle { get; }

Related types: Text

Body

Gets the main body text of the card.

The value, or null when it was not set.

public Text? Body { get; }

Related types: Text

Actions

Gets buttons displayed at the bottom of the card, in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<ButtonElement> Actions { get; }

Related types: ButtonElement

SlackIcon

Gets a Slack-provided icon displayed beside the title. Cannot be combined with an image icon.

The value, or null when it was not set.

public SlackIcon? SlackIcon { get; }

Related types: SlackIcon

Subtext

Gets the small print shown at the bottom of the card.

The value, or null when it was not set.

public Text? Subtext { get; }

Related types: Text

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

CarouselBlock

A horizontally scrolling set of cards, available in messages and App Home.

• Required: elements.

See the Slack reference.

Implements IBlock.

CarouselBlock

Creates and validates a CarouselBlock.

public CarouselBlock(IEnumerable<CardBlock> elements, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
elements	The cards in display order. Required. Must contain between 1 and 10 items.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: CardBlock, CarouselBlock

Elements

Gets the cards in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<CardBlock> Elements { get; }

Related types: CardBlock

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

ContainerBlock

A titled group of blocks that can optionally collapse.

• Required: childBlocks.
• Provide a title or a rich text title.

See the Slack reference.

Implements IBlock.

ContainerBlock

Creates and validates a ContainerBlock.

public ContainerBlock(IEnumerable<IBlock> childBlocks, PlainText? title = null, RichTextBlock? richTextTitle = null, Text? subtitle = null, ContainerWidth? width = null, ImageElement? icon = null, bool? isCollapsible = null, bool? defaultCollapsed = null, bool? hasHeaderDivider = null, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
childBlocks	The blocks grouped inside the container, in display order. Required. Must contain between 1 and 10 items.
title	The container title. Provide either a title or a rich text title. Slack allows at most 150 characters. A string is sent as a plain_text text object.
richTextTitle	A rich text block used as the title in place of a plain-text title.
subtitle	The supporting text shown below the title. Slack allows at most 150 characters. A string is sent as a mrkdwn text object.
width	The horizontal width of the container.
icon	The image displayed beside the title.
isCollapsible	Whether users can collapse and expand the container.
defaultCollapsed	Whether a collapsible container starts collapsed. Requires the container to be collapsible.
hasHeaderDivider	Whether Slack draws a divider below the container header. Only valid for non-collapsible containers.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: ContainerBlock, ContainerWidth, IBlock, ImageElement, PlainText, RichTextBlock, Text

ChildBlocks

Gets the blocks grouped inside the container, in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<IBlock> ChildBlocks { get; }

Related types: IBlock

Title

Gets the container title. Provide either a title or a rich text title.

The value, or null when it was not set.

public PlainText? Title { get; }

Related types: PlainText

RichTextTitle

Gets a rich text block used as the title in place of a plain-text title.

The value, or null when it was not set.

public RichTextBlock? RichTextTitle { get; }

Related types: RichTextBlock

Subtitle

Gets the supporting text shown below the title.

The value, or null when it was not set.

public Text? Subtitle { get; }

Related types: Text

Width

Gets the horizontal width of the container.

The value, or null when it was not set.

public ContainerWidth? Width { get; }

Related types: ContainerWidth

Icon

Gets the image displayed beside the title.

The value, or null when it was not set.

public ImageElement? Icon { get; }

Related types: ImageElement

IsCollapsible

Gets whether users can collapse and expand the container.

The value, or null when it was not set.

public bool? IsCollapsible { get; }

DefaultCollapsed

Gets whether a collapsible container starts collapsed. Requires the container to be collapsible.

The value, or null when it was not set.

public bool? DefaultCollapsed { get; }

HasHeaderDivider

Gets whether Slack draws a divider below the container header. Only valid for non-collapsible containers.

The value, or null when it was not set.

public bool? HasHeaderDivider { get; }

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

ContainerWidth

Widths supported by Slack container blocks.

ToWireValue() returns the value Slack expects in JSON.

Constant	Slack value	Meaning
Narrow	narrow	A compact container.
Standard	standard	Slack's standard container width.
Wide	wide	A wide container.
Full	full	The full available width.

ContextActionsBlock

A row of feedback or icon buttons, usually shown below AI-generated content.

• Required: elements.

See the Slack reference.

Implements IBlock.

ContextActionsBlock

Creates and validates a ContextActionsBlock.

public ContextActionsBlock(IEnumerable<IContextActionsElement> elements, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
elements	Feedback buttons or icon buttons in display order. Required. Slack allows at most 5 items.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: ContextActionsBlock, IContextActionsElement

Elements

Gets feedback buttons or icon buttons in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<IContextActionsElement> Elements { get; }

Related types: IContextActionsElement

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

ContextBlock

A block of small, secondary images and text.

• Required: elements.

See the Slack reference.

Implements IBlock.

ContextBlock

Creates and validates a ContextBlock.

public ContextBlock(IEnumerable<IContextElement> elements, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
elements	Images and text in display order. Required. Slack allows at most 10 items.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: ContextBlock, IContextElement

Elements

Gets images and text in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<IContextElement> Elements { get; }

Related types: IContextElement

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

DataTableBlock

A sortable, paginated table of raw text, numbers, and rich text.

• Required: rows, caption.
• The first row is the header row and cannot contain rich text.
• Every row must have the same number of cells, and all cell text together is limited to 20,000 characters.

See the Slack reference.

Implements IBlock.

DataTableBlock

Creates and validates a DataTableBlock.

public DataTableBlock(IEnumerable<IEnumerable<IDataTableCell>> rows, string caption, int? pageSize = null, int? rowHeaderColumnIndex = null, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
rows	Complete table rows in display order. Every row must have the same number of cells. Required. Must contain between 2 and 201 items.
caption	The caption that describes the table's contents. Required.
pageSize	How many rows Slack shows per page. Must be between 1 and 100.
rowHeaderColumnIndex	The zero-based index of the column whose cells act as row headers. Must be at least 0.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: DataTableBlock, IDataTableCell

Rows

Gets complete table rows in display order. Every row must have the same number of cells.

The values in order, or an empty list when none were set.

public IReadOnlyList<IReadOnlyList<IDataTableCell>> Rows { get; }

Related types: IDataTableCell

Caption

Gets the caption that describes the table's contents.

public string Caption { get; }

PageSize

Gets how many rows Slack shows per page.

public int? PageSize { get; }

RowHeaderColumnIndex

Gets the zero-based index of the column whose cells act as row headers.

public int? RowHeaderColumnIndex { get; }

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

DataVisualizationBlock

A titled pie, bar, area, or line chart.

• Required: title, chart.

See the Slack reference.

Implements IBlock.

DataVisualizationBlock

Creates and validates a DataVisualizationBlock.

public DataVisualizationBlock(string title, IChart chart, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
title	The chart title. Required. Slack allows at most 50 characters.
chart	The chart to display. Required.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: DataVisualizationBlock, IChart

Title

Gets the chart title.

public string Title { get; }

Chart

Gets the chart to display.

public IChart Chart { get; }

Related types: IChart

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

DividerBlock

A horizontal rule that separates blocks.

See the Slack reference.

Implements IBlock.

DividerBlock

Creates and validates a DividerBlock.

public DividerBlock(string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: DividerBlock

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

FileBlock

A remote file previously added with the files.remote API.

• Required: externalId, source.

See the Slack reference.

Implements IBlock.

FileBlock

Creates and validates a FileBlock.

public FileBlock(string externalId, string? source = null, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
externalId	The external identifier of a remote file previously added with the files.remote API. Required.
source	The file source. Slack currently supports only remote files. Required.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: FileBlock

ExternalId

Gets the external identifier of a remote file previously added with the files.remote API.

public string ExternalId { get; }

Source

Gets the file source. Slack currently supports only remote files.

public string? Source { get; }

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

HeaderBlock

Large, bold plain text that introduces a group of blocks.

• Required: text.

See the Slack reference.

Implements IBlock.

HeaderBlock

Creates and validates a HeaderBlock.

public HeaderBlock(PlainText text, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
text	The header text, shown in a larger bold font. Required. Slack allows at most 150 characters. A string is sent as a plain_text text object.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: HeaderBlock, PlainText

Text

Gets the header text, shown in a larger bold font.

public PlainText Text { get; }

Related types: PlainText, Text

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

IBlock

A validated Slack layout block accepted directly by Slack's official Java SDK.

Implemented by ActionsBlock, AlertBlock, CardBlock, CarouselBlock, ContainerBlock, ContextActionsBlock, ContextBlock, DataTableBlock, DataVisualizationBlock, DividerBlock, FileBlock, HeaderBlock, ImageBlock, InputBlock, MarkdownBlock, PlanBlock, RichTextBlock, SectionBlock, TableBlock, TaskCardBlock, VideoBlock.

IContextActionsElement

A value that can appear in a context actions block: feedback buttons or an icon button.

Implemented by FeedbackButtonsElement, IconButtonElement.

IContextElement

A value that can appear in a context block: an image element or a text object.

Implemented by ImageElement, MarkdownText, PlainText.

IDataTableCell

A value that can appear as a data table cell: raw text, a raw number, or a rich text block.

Implemented by RawNumber, RawText, RichTextBlock.

ImageBlock

A standalone image with alternative text and an optional title.

• Required: altText.
• Provide exactly one of an image URL or a Slack file.

See the Slack reference.

Implements IBlock.

ImageBlock

Creates and validates a ImageBlock.

public ImageBlock(string? imageUrl, string altText, PlainText? title = null, string? blockId = null, SlackFile? slackFile = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
imageUrl	The publicly accessible URL of the image. Cannot be combined with a Slack file. Slack allows at most 3000 characters.
altText	A plain-text summary of the image or video for assistive technology. Required. Slack allows at most 2000 characters.
title	The title shown above the image. Slack allows at most 2000 characters. A string is sent as a plain_text text object.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
slackFile	A file hosted in Slack as the image source. Cannot be combined with an image URL.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: ImageBlock, PlainText, SlackFile

ImageUrl

Gets the publicly accessible URL of the image. Cannot be combined with a Slack file.

The value, or null when it was not set.

public string? ImageUrl { get; }

SlackFile

Gets a file hosted in Slack as the image source. Cannot be combined with an image URL.

The value, or null when it was not set.

public SlackFile? SlackFile { get; }

Related types: SlackFile

AltText

Gets a plain-text summary of the image or video for assistive technology.

public string AltText { get; }

Title

Gets the title shown above the image.

The value, or null when it was not set.

public PlainText? Title { get; }

Related types: PlainText

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

InputBlock

A labelled input that collects a value in a modal, App Home, or message.

• Required: label, element.

See the Slack reference.

Implements IBlock.

InputBlock

Creates and validates a InputBlock.

public InputBlock(PlainText label, IInputElement element, bool? dispatchAction = null, string? blockId = null, PlainText? hint = null, bool? optional = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
label	The label shown above the input. Required. Slack allows at most 2000 characters. A string is sent as a plain_text text object.
element	The input element that collects the user's value. Required.
dispatchAction	Whether changing the element sends a block_actions payload immediately.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
hint	Helper text shown below the input. Slack allows at most 2000 characters. A string is sent as a plain_text text object.
optional	Whether the modal can be submitted when this input is empty.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: IInputElement, InputBlock, PlainText

Label

Gets the label shown above the input.

public PlainText Label { get; }

Related types: PlainText

Element

Gets the input element that collects the user's value.

public IInputElement Element { get; }

Related types: IInputElement

DispatchAction

Gets whether changing the element sends a block_actions payload immediately.

The value, or null when it was not set.

public bool? DispatchAction { get; }

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

Hint

Gets helper text shown below the input.

The value, or null when it was not set.

public PlainText? Hint { get; }

Related types: PlainText

Optional

Gets whether the modal can be submitted when this input is empty.

The value, or null when it was not set.

public bool? Optional { get; }

ITableCell

A value that can appear as a table block cell: raw text or a rich text block.

Implemented by RawText, RichTextBlock.

MarkdownBlock

Standard markdown rendered by Slack, intended for AI-generated content.

• Required: text.

See the Slack reference.

Implements IBlock.

MarkdownBlock

Creates and validates a MarkdownBlock.

public MarkdownBlock(string text, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
text	Standard markdown content, which Slack renders directly. Required. Slack allows at most 12000 characters.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: MarkdownBlock

Text

Gets standard markdown content, which Slack renders directly.

public string Text { get; }

Related types: Text

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

PlanBlock

A titled sequence of task cards.

• Required: title, tasks.
• Task IDs must be unique within a plan.

See the Slack reference.

Implements IBlock.

PlanBlock

Creates and validates a PlanBlock.

public PlanBlock(string title, IEnumerable<TaskCardBlock>? tasks = null, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
title	The plan title. Required.
tasks	Task cards in display order. Required. Slack allows at most 50 items.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: PlanBlock, TaskCardBlock

Title

Gets the plan title.

public string Title { get; }

Tasks

Gets task cards in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<TaskCardBlock> Tasks { get; }

Related types: TaskCardBlock

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

RichTextBlock

Formatted text built from sections, lists, preformatted blocks, and quotes.

• Required: elements.

See the Slack reference.

Implements IBlock, IDataTableCell, ITableCell.

RichTextBlock

Creates and validates a RichTextBlock.

public RichTextBlock(IEnumerable<IRichTextBlockElement> elements, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
elements	Sections, lists, preformatted blocks, and quotes in display order. Required.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: IRichTextBlockElement, RichTextBlock

Elements

Gets sections, lists, preformatted blocks, and quotes in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<IRichTextBlockElement> Elements { get; }

Related types: IRichTextBlockElement

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

SectionBlock

Text, a grid of fields, or both, with an optional accessory element.

• Provide text, fields, or both.

See the Slack reference.

Implements IBlock.

SectionBlock

Creates and validates a SectionBlock.

public SectionBlock(Text? text = null, IEnumerable<Text>? fields = null, IElement? accessory = null, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
text	The main text of the section. Slack allows at most 3000 characters. A string is sent as a mrkdwn text object.
fields	Section fields, shown in a two-column grid, in display order. Slack allows at most 10 items, each at most 2000 characters. Strings are sent as mrkdwn text objects.
accessory	The element displayed beside the section text.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: IElement, SectionBlock, Text

Text

Gets the main text of the section.

The value, or null when it was not set.

public Text? Text { get; }

Related types: Text

Fields

Gets section fields, shown in a two-column grid, in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<Text> Fields { get; }

Related types: Text

Accessory

Gets the element displayed beside the section text.

The value, or null when it was not set.

public IElement? Accessory { get; }

Related types: IElement

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

TableBlock

A simple table of raw text and rich text cells.

• Required: rows.

See the Slack reference.

Implements IBlock.

TableBlock

Creates and validates a TableBlock.

public TableBlock(IEnumerable<IEnumerable<ITableCell>> rows, IEnumerable<ColumnSettings>? columnSettings = null, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
rows	Complete table rows in display order. Required. Slack allows at most 100 items.
columnSettings	Per-column settings in column order. Provide one entry for every column. Slack allows at most 20 items.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: ColumnSettings, ITableCell, TableBlock

Rows

Gets complete table rows in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<IReadOnlyList<ITableCell>> Rows { get; }

Related types: ITableCell

ColumnSettings

Gets per-column settings in column order. Provide one entry for every column.

The values in order, or an empty list when none were set.

public IReadOnlyList<ColumnSettings> ColumnSettings { get; }

Related types: ColumnSettings

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

TaskCardBlock

One task with its status, details, output, and sources.

• Required: taskId, title, status.
• A standalone task card's status cannot be pending; pending is only valid for plan tasks.

See the Slack reference.

Implements IBlock.

TaskCardBlock

Creates and validates a TaskCardBlock.

public TaskCardBlock(string taskId, string title, RichTextBlock? details = null, RichTextBlock? output = null, IEnumerable<UrlSource>? sources = null, TaskCardStatus? status = null, string? blockId = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
taskId	The identifier of the task. Required.
title	The task title. Required.
details	A rich text description of the task.
output	Rich text describing the task's output.
sources	Links to the sources the task used, in display order.
status	The task's current state. Required.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: RichTextBlock, TaskCardBlock, TaskCardStatus, UrlSource

TaskId

Gets the identifier of the task.

public string TaskId { get; }

Title

Gets the task title.

public string Title { get; }

Details

Gets a rich text description of the task.

The value, or null when it was not set.

public RichTextBlock? Details { get; }

Related types: RichTextBlock

Output

Gets rich text describing the task's output.

The value, or null when it was not set.

public RichTextBlock? Output { get; }

Related types: RichTextBlock

Sources

Gets links to the sources the task used, in display order.

The values in order, or an empty list when none were set.

public IReadOnlyList<UrlSource> Sources { get; }

Related types: UrlSource

Status

Gets the task's current state.

The value, or null when it was not set.

public TaskCardStatus? Status { get; }

Related types: TaskCardStatus

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

TaskCardStatus

States supported by task card blocks.

ToWireValue() returns the value Slack expects in JSON.

Constant	Slack value	Meaning
Pending	pending	The task has not started.
InProgress	in_progress	The task is running.
Complete	complete	The task finished successfully.
Error	error	The task failed.

VideoBlock

An embedded video player.

• Required: altText, thumbnailUrl, title, videoUrl.

See the Slack reference.

Implements IBlock.

VideoBlock

Creates and validates a VideoBlock.

public VideoBlock(string altText, string thumbnailUrl, PlainText title, string videoUrl, string? blockId = null, string? authorName = null, PlainText? description = null, string? providerIconUrl = null, string? providerName = null, string? titleUrl = null, IReadOnlyDictionary<string, object?>? additionalFields = null)

Parameter	Description
altText	A plain-text summary of the image or video for assistive technology. Required. Slack allows at most 2000 characters.
thumbnailUrl	The URL of the image shown before the video plays. Required. Slack allows at most 3000 characters.
title	The video title. Required. Slack allows at most 200 characters. A string is sent as a plain_text text object.
videoUrl	The embeddable URL of the video. The domain must be listed in the app's unfurl domains. Required. Slack allows at most 3000 characters.
blockId	A unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again. Slack allows at most 255 characters.
authorName	The name of the video's author. Slack allows at most 50 characters.
description	The video description. Slack allows at most 200 characters. A string is sent as a plain_text text object.
providerIconUrl	The URL of the video provider's icon. Slack allows at most 2000 characters.
providerName	The name of the video provider, such as YouTube. Slack allows at most 50 characters.
titleUrl	The HTTPS URL opened when the title is clicked. Slack allows at most 2000 characters.
additionalFields	Slack fields that have no named parameter yet, such as a field Slack introduced after this release. Values must be strings, numbers, booleans, lists, dictionaries, JSON nodes, or slackblocks values, and are validated with the rest of the object. Typed properties do not reflect them, and a field cannot be set both here and through its named parameter.

Throws	When
ValidationException	The value breaks a Block Kit rule, such as a missing required field or an exceeded length limit.
ArgumentException	A collection contains null, or an additional field cannot be written as JSON or repeats a named parameter.

Related types: PlainText, VideoBlock

AltText

Gets a plain-text summary of the image or video for assistive technology.

public string AltText { get; }

ThumbnailUrl

Gets the URL of the image shown before the video plays.

public string ThumbnailUrl { get; }

Title

Gets the video title.

public PlainText Title { get; }

Related types: PlainText

VideoUrl

Gets the embeddable URL of the video. The domain must be listed in the app's unfurl domains.

public string VideoUrl { get; }

BlockId

Gets a unique identifier for this block. Slack returns it in interaction payloads, so use a stable value when you need to find the block again.

The value, or null when it was not set.

public string? BlockId { get; }

AuthorName

Gets the name of the video's author.

The value, or null when it was not set.

public string? AuthorName { get; }

Description

Gets the video description.

The value, or null when it was not set.

public PlainText? Description { get; }

Related types: PlainText

ProviderIconUrl

Gets the URL of the video provider's icon.

The value, or null when it was not set.

public string? ProviderIconUrl { get; }

ProviderName

Gets the name of the video provider, such as YouTube.

The value, or null when it was not set.

public string? ProviderName { get; }

TitleUrl

Gets the HTTPS URL opened when the title is clicked.

The value, or null when it was not set.

public string? TitleUrl { get; }