I tried the new blocks in Slack Block Kit [General Display Edition]

Since entering 2026, new blocks have been added one after another to Slack's Block Kit. In this series, we will introduce these new blocks while actually trying them out.

• Part 1: Data edition

https://dev.classmethod.jp/articles/slack-block-kit-new-data-display-blocks/

• Part 2: General display edition (this article)
• Part 3: Agent edition
• Part 4: Streaming edition
• Part 5: Verification/CI edition

For this second installment, we will look at 5 general-purpose display blocks: alert / card / carousel / container / markdown.

Overview of the 5 Blocks

The markdown block was added back in February 2025, making it somewhat older, but since its supported syntax was expanded in March 2026 to include tables, task lists, and more^[4], we will introduce it in this article as well.

The official Slack blog describes card as being used for hierarchical display of information, and alert for visually representing severity levels^[5].

Verification is performed in Block Kit Builder, as in the previous installment.

alert block

This block expresses severity levels with colors^[6].

As a note, alert blocks cannot be used in messages and can only be placed in modals. Therefore, in Block Kit Builder, switch to modal mode before pasting.

{
  "type": "modal",
  "title": { "type": "plain_text", "text": "Deploy Confirmation" },
  "submit": { "type": "plain_text", "text": "Execute" },
  "close": { "type": "plain_text", "text": "Cancel" },
  "blocks": [
    {
      "type": "alert",
      "level": "warning",
      "text": {
        "type": "mrkdwn",
        "text": "*This is a production environment deployment.* Please complete verification in staging before proceeding."
      }
    }
  ]
}

Since this is exactly the kind of block you'd want to use for deploy or error notifications, it's a bit surprising that it can't be placed in messages. We look forward to support for additional surfaces in the future.

card block

This block combines an icon, title, body text, and buttons into a single card^[7].

{
  "blocks": [
    {
      "type": "card",
      "title": { "type": "mrkdwn", "text": "v2.4.0 Release Notes" },
      "subtitle": { "type": "mrkdwn", "text": "Published 2026-08-25" },
      "body": { "type": "mrkdwn", "text": "Includes search performance improvements and a bug fix for notification settings." },
      "actions": [
        {
          "type": "button",
          "text": { "type": "plain_text", "text": "View Details" },
          "action_id": "view_release"
        }
      ]
    }
  ]
}

Layouts that previously required combining section, context, and actions can now be completed with a single block, improving readability as well.

carousel block

This block arranges cards in a horizontal scroll^[8]. The only field is elements, which holds a minimum of 1 and a maximum of 10 cards. Blocks other than card cannot be included.

{
  "blocks": [
    {
      "type": "carousel",
      "elements": [
        {
          "type": "card",
          "block_id": "release-240",
          "title": { "type": "mrkdwn", "text": "v2.4.0" },
          "body": { "type": "mrkdwn", "text": "Search performance improvements" }
        },
        {
          "type": "card",
          "block_id": "release-232",
          "title": { "type": "mrkdwn", "text": "v2.3.2" },
          "body": { "type": "mrkdwn", "text": "Bug fix for notification settings" }
        }
      ]
    }
  ]
}

It is well-suited for situations where multiple pieces of information with the same structure need to be presented, such as options or search results.

container block

This block groups multiple blocks together with a title^[9]. It supports collapsing.

{
  "blocks": [
    {
      "type": "container",
      "title": { "type": "plain_text", "text": "Weekly Report: Week of 8/24" },
      "subtitle": { "type": "plain_text", "text": "Expand to view details" },
      "is_collapsible": true,
      "child_blocks": [
        {
          "type": "section",
          "text": { "type": "mrkdwn", "text": "*Inquiry count*: 99 (up 12 from previous week)" }
        },
        { "type": "divider" },
        {
          "type": "context",
          "elements": [{ "type": "mrkdwn", "text": "Reporting period: 8/24–8/30" }]
        }
      ]
    }
  ]
}

As a limitation, card, markdown, and data_table introduced in the previous installment cannot be placed as child elements. Since table can be included, if you want to collapse a table, you will need to use the table block.

markdown block

This block can display text in standard Markdown format^[10].

In Slack's own mrkdwn syntax, bold is written as *bold*, but in this block, standard Markdown's **bold** can be used.

This block appears to be designed for use cases such as displaying LLM responses that are already formatted in Markdown.

{
  "blocks": [
    {
      "type": "markdown",
      "text": "## Incident Response Log\n\n**Search API latency had degraded**.\n\n| Time | Status |\n| --- | --- |\n| 10:02 | Detected |\n| 10:30 | Resolved |\n\n- [x] Root cause identified\n- [ ] Prevention measures implemented"
    }
  ]
}

It's very convenient that tables and task lists render directly!

Summary

In this article, we looked at 5 blocks: alert / card / carousel / container / markdown.

All of these blocks can be easily tried by simply pasting the JSON from this article into Block Kit Builder, so please give any blocks that caught your interest a try.

In the next installment, Part 3, we will try out the agent-related blocks, which are attracting particularly high attention. Stay tuned!