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/slack-block-kit

@f71635f
by Chris Cheneyccheney/robust-skills61 stars
3

Build or debug Slack Block Kit payloads for messages, modals, App Home, streaming responses, and Work Object unfurls. Use for block layout, elements, or interaction schemas; not plain Slack text formatting alone.

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Use this Skill: https://skilld.dev/gh/ccheney/robust-skills/slack-block-kit

This session only. Nothing lands on disk.

referencesCHEATSHEET.md

≈2.5k tokens on demand. Your agent reads this file only when SKILL.md points to it.

Slack Block Kit Quick Reference

Sources:

Block Types

Block Type String Surfaces Key Limits
Header header Msg, Modal, Home 150 chars, plain_text only; optional level 1-4
Section section Msg, Modal, Home 3000 chars text, 10 fields (2000 each), 1 accessory
Divider divider Msg, Modal, Home No fields
Context context Msg, Modal, Home 10 elements (text + image)
Actions actions Msg, Modal, Home 25 elements
Alert alert Modal only 200 chars. Levels: default/info/warning/error/success
Card card Msg, Modal, Home Title/subtitle 150, body/subtext 200 chars, max 3 buttons
Carousel carousel Msg, Home 1-10 card elements
Container container Msg title or rich_text_title, max 10 child blocks, collapsible; optional non-collapsible header divider
Image image Msg, Modal, Home alt_text required, png/jpg/gif
Rich Text rich_text Msg, Modal, Home Nested sub-elements
Table table Msg, Home 100 rows, 20 cols. 10K chars/table and per msg. No semantic header schema. Rows are flat cell arrays; no columns prop
Data Table data_table Msg, Home caption required. Header + 1-200 rows, 20K chars, page_size 1-100 (default 5). Sortable/paginated
Data Visualization data_visualization Msg only Title ≤50. pie/bar/area/line. 1-12 series/segments, 1-20 points, labels ≤20
Markdown markdown Msg only 12K chars cumulative, standard MD incl. tables, task lists, dividers, syntax-highlighted code; variable header sizes rolling out
Context Actions context_actions Msg only 5 elements
Input input Modal, Msg, Home label required, many element types
Video video Msg, Modal, Home links.embed:write scope
Plan plan Msg only Sequential task cards for AI agent output
Task Card task_card Msg only Single task with status, details, output, sources
File file Retrieval only Read-only, source: "remote"; apps cannot author it

The current markdown-block reference says all header levels render at the same size, while Slack's March 6, 2026 changelog says variable-sized headers are rolling out. Use semantic levels and expect temporary client/workspace variation.

Interactive Elements

Element Type String Compatible Blocks
Button button section, actions; card has a separate button-shaped actions array
Overflow Menu overflow section, actions
Select Menu static_select / external_select / users_select / conversations_select / channels_select section, actions, input
Multi-Select multi_static_select / multi_external_select / multi_users_select / multi_conversations_select / multi_channels_select section, actions, input
Date Picker datepicker section, actions, input
Time Picker timepicker section, actions, input
Datetime Picker datetimepicker actions, input
Checkboxes checkboxes section, actions, input
Radio Buttons radio_buttons section, actions, input
Plain Text Input plain_text_input input
Number Input number_input input
Email Input email_text_input input
URL Input url_text_input input
Rich Text Input rich_text_input input
File Input file_input input
Feedback Buttons feedback_buttons context_actions
Icon Button icon_button context_actions
Image image section (accessory), context
Workflow Button workflow_button section, actions
URL Source url task_card (sources array)

Composition Objects

Object Used In
Text (mrkdwn / plain_text) Most blocks and elements
Option Select menus, overflow, checkboxes, radio buttons
Option Group Select menus (grouped options)
Confirmation Dialog Elements that expose a confirm property
Conversation Filter Conversation select menus (via filter)
Dispatch Action Config plain/rich/number/email/URL text-like inputs
Slack File Image block/element (via slack_file)
Slack Icon Card block (via slack_icon)
Trigger Workflow button (via workflow.trigger)
Input Parameter Workflow trigger customizable_input_parameters
Workflow Workflow button (wraps trigger object)

Rich Text Sub-Elements

Sub-Element Purpose Key Properties
rich_text_section Paragraph elements (inline array)
rich_text_list Bullet/ordered list style, indent, offset, border
rich_text_preformatted Code block elements, border
rich_text_quote Blockquote elements, border

Inline Elements

Type Key Properties
text text, style: { bold, italic, strike, underline, highlight, client_highlight, unlink }
link url, text, style
emoji name
user user_id
channel channel_id
usergroup usergroup_id
broadcast range (here/channel/everyone)
date timestamp, format, fallback
color value (hex)

The current index also defines attachment_mention, canvas, canvas_message_unfurl, canvas_user_mention, citation, file, list_record, message_mention, salesforce_data_field, tag, team, work_object_mention, and workflow_mention. Sections, list-item sections, and quotes accept the broad inline set; rich_text_preformatted accepts only text and link. See RICH-TEXT.md before authoring specialized/output-oriented types.

Button Styles

Style Color Usage
(default) Gray Standard actions
primary Green Affirmation — use sparingly, one per set
danger Red Destructive — use with confirmation dialog

Limits at a Glance

What Limit
Blocks per message 50
Blocks per modal/Home 100
Section text 3000 chars
Section fields 10 items
Header text 150 chars
Context elements 10
Actions elements 25
Alert text 200 chars (modals only)
Card title / subtitle / body / subtext 150 / 150 / 200 / 200 chars
Card action buttons 3
Carousel cards 1-10
Container child blocks / title 10 / 150 chars
Table rows / cols 100 / 20
Table cell chars (per table & per msg) 10,000
Data table rows / cell chars header + 200 / 20,000 per table and per message
Data viz series/segments / points 1-12 / 1-20
Modal title 24 chars
Modal views stack 3
Button text 75 chars
action_id / block_id 255 chars
Select options 100
Overflow options 5
Placeholder text 150 chars
File input max size 100MB per file
Rich text input lines min_lines/max_lines 1-100; maximum defaults to 8
Streaming chunk fields (task/plan update) 256 chars

Streaming (chat.startStream / appendStream / stopStream)

What Detail
Scope chat:write
Start requires channel, thread_ts (+ recipient_user_id, recipient_team_id for channels)
Append requires channel, streaming message ts, plus at least one of markdown_text or chunks per the official Node SDK contract
Stop requires channel, streaming message ts
Chunk types markdown_text (text field), flat task_update, flat plan_update, blocks
task_display_mode timeline (default), plan, dense
Blocks per chunk array 50 (extras dropped with warning)
Top-level blocks Only stopStream; rendered below final stream, separate 50-block limit
Rate limits start/stop Tier 2 (20+/min), append Tier 4 (100+/min)

The live Web API field table marks append markdown_text required and chunks optional. In contrast, the official Node SDK marks both optional but says either is required, the Python SDK accepts both as optional, and the Developing an agent guide shows chunks-only append. For SDK calls, provide at least one; raw-HTTP callers should check the current method schema before omitting markdown_text and include it whenever that schema still marks it required. Validate chunk shapes against the current method reference and SDK model.

Surfaces

Surface Block Kit Key Method
Messages Yes (50 blocks) chat.postMessage
Modals Yes (100 blocks) views.open
App Home Yes (100 blocks) views.publish
Canvases No (markdown only) canvases.create
Lists No lists.*
Agent Messages agent_view (new apps) Standard Messages tab with threads
Legacy Assistant assistant_view (existing apps) Chat + History; eventual deprecation

Work Object Entity Types

Type Entity ID
File slack#/entities/file
Task slack#/entities/task
Incident slack#/entities/incident
Content Item slack#/entities/content_item
Item slack#/entities/item

Unfurl entities live at metadata.entities[] and require per-entity app_unfurl_url, url, external_ref, entity_type, and entity_payload. entity_comments is the sibling bidirectional-comments envelope; see WORK-OBJECTS.md.

Source: SKILL.md on GitHub

Third-party checks

No alerts15d4 checks · Risk SAFE
  • Gen Agent Trust Hub15d

    This skill is a technical reference for Slack Block Kit. It provides detailed API documentation, schema requirements, and security guidelines for building Slack payloads. No malicious code or risky patterns were found.

  • Socket15d

    No alerts

  • Snyk15d

    Risk: LOW · No issues

  • Runlayer7mo

    8 files scanned · No issues

Provenance

Signed by skilld at f71635f. This ties the file your Agent reads to that commit on GitHub. It does not review the instructions.

Last checked against GitHub 3 weeks ago.

Activeupdated 3 weeks ago

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