Attachment object

Slack’s legacy secondary attachment: content in a box with a coloured bar down its side, sent in a message’s attachments array next to (or instead of) blocks.

Usage

Attachments are not blocks. Send them in the message’s top-level attachments array — on chat.postMessage, chat.update, chat.postEphemeral, response_url replies and the v1 chat message endpoints. The API hands them back as attachments, never inside blocks.

Slack treats attachments as legacy; prefer blocks for new apps. They are still handy for a coloured status bar, or to wrap blocks in one: put Block Kit blocks in the attachment’s blocks field and they render inside the box, controls included.

A message can carry up to 20 attachments, shown after its blocks. When a message has attachments but no blocks, its top-level text is shown above them.

Inside the box, Repzo shows the author line, the title, text, fields, blocks, image_url and then the footer; pretext sits above the box and thumb_url beside it.

A status update with fields

{
  "text": "Weekly pipeline update",
  "attachments": [
    {
      "color": "good",
      "fallback": "Northwind Trading renewal moved to Negotiation (SAR 48,000)",
      "pretext": "A deal moved forward in *Enterprise renewals*.",
      "author_name": "Pipeline bot",
      "title": "Northwind Trading renewal",
      "title_link": "https://example.com/deals/northwind-renewal",
      "text": "Stage changed from *Proposal* to *Negotiation*. Next step: send the revised quote by Thursday.",
      "fields": [
        {
          "title": "Amount",
          "value": "SAR 48,000",
          "short": true
        },
        {
          "title": "Close date",
          "value": "Nov 28, 2026",
          "short": true
        },
        {
          "title": "Owner",
          "value": "<@3f6c2a1e-8b4d-4c7a-9e21-5d0b7f9a1c34|Account owner>",
          "short": true
        },
        {
          "title": "Probability",
          "value": "70%",
          "short": true
        }
      ],
      "footer": "Repzo CRM",
      "ts": 1791813600
    }
  ]
}

Blocks inside an attachment

{
  "attachments": [
    {
      "color": "#e01e5a",
      "fallback": "Invoice INV-2041 is 15 days overdue",
      "blocks": [
        {
          "type": "section",
          "text": {
            "type": "mrkdwn",
            "text": "*Invoice INV-2041* for *Blue Harbor Logistics* is 15 days overdue.\nBalance due: *SAR 12,450*"
          }
        },
        {
          "type": "actions",
          "elements": [
            {
              "type": "button",
              "text": {
                "type": "plain_text",
                "text": "Send reminder"
              },
              "style": "primary",
              "action_id": "send_reminder",
              "value": "INV-2041"
            },
            {
              "type": "button",
              "text": {
                "type": "plain_text",
                "text": "Open invoice"
              },
              "url": "https://example.com/invoices/INV-2041",
              "action_id": "open_invoice"
            }
          ]
        }
      ]
    }
  ]
}

Fields

Field	Type	Description	Required?
color	String	Colour of the bar down the side of the box: good (green), warning (yellow), danger (red) or a hex colour code such as #439FE0 (3 or 6 digits, # optional).	Optional
fallback	String	A plain-text summary of the attachment. Used in notifications and message previews, and as the image’s alternative text. Recommended.	Optional
pretext	String	Text shown above the box. Formatted as mrkdwn.	Optional
author_name	String	Small text naming the author, shown at the top of the box.	Optional
author_link	String	An http(s) URL that author_name links to. Only works when author_name is set.	Optional
author_icon	String	An http(s) URL of a small (16×16) image shown before author_name. Only works when author_name is set.	Optional
title	String	Larger, bold text near the top of the box.	Optional
title_link	String	An http(s) URL that title links to.	Optional
text	String	The main body text of the attachment. Formatted as mrkdwn.	Optional
fields	Object[]	A table of values shown under text. Each field is { "title": String, "value": String, "short": Boolean }: title is a plain-text heading, value is mrkdwn (numbers are turned into strings), and short: true lets two fields sit side by side.	Optional
image_url	String	An http(s) URL of an image shown full width inside the box.	Optional
thumb_url	String	An http(s) URL of a small image shown on the right of the box.	Optional
footer	String	Small text at the bottom of the box.	Optional
footer_icon	String	An http(s) URL of a small (16×16) image shown before footer.	Optional
ts	Number	A Unix timestamp (seconds; a numeric string also works). Shown in the footer as a date.	Optional
mrkdwn_in	String[]	Which of pretext, text and fields to format as mrkdwn.	Optional
blocks	Object[]	Block Kit blocks shown inside the box. They follow the same rules as top-level blocks and share the message’s block_id space, so their controls send block_actions like any other.	Optional

How Repzo Chat differs from Slack

• text is formatted as mrkdwn unless mrkdwn_in is sent and leaves text out; then it shows exactly as written, line breaks kept. pretext and field values are always formatted as mrkdwn.
• Legacy attachment buttons (actions, callback_id) aren’t supported and return a warning. Put an actions block in the attachment’s blocks instead.
• ts is shown as the date only (YYYY-MM-DD), not as a relative time.
• A color that isn’t good, warning, danger or a hex code returns a warning and the box has no coloured bar. An attachment with nothing to show also returns a warning.
• Other legacy fields (author_subname, image_bytes, thumb_width, id, …) are dropped.

Examples

A status update with fields

Sent as text + attachments, without blocks: the text shows above the coloured box.

{
  "text": "Weekly pipeline update",
  "attachments": [
    {
      "color": "good",
      "fallback": "Northwind Trading renewal moved to Negotiation (SAR 48,000)",
      "pretext": "A deal moved forward in *Enterprise renewals*.",
      "author_name": "Pipeline bot",
      "title": "Northwind Trading renewal",
      "title_link": "https://example.com/deals/northwind-renewal",
      "text": "Stage changed from *Proposal* to *Negotiation*. Next step: send the revised quote by Thursday.",
      "fields": [
        {
          "title": "Amount",
          "value": "SAR 48,000",
          "short": true
        },
        {
          "title": "Close date",
          "value": "Nov 28, 2026",
          "short": true
        },
        {
          "title": "Owner",
          "value": "<@3f6c2a1e-8b4d-4c7a-9e21-5d0b7f9a1c34|Account owner>",
          "short": true
        },
        {
          "title": "Probability",
          "value": "70%",
          "short": true
        }
      ],
      "footer": "Repzo CRM",
      "ts": 1791813600
    }
  ]
}

Blocks inside an attachment

An attachment’s blocks render inside the box, with working buttons.

{
  "attachments": [
    {
      "color": "#e01e5a",
      "fallback": "Invoice INV-2041 is 15 days overdue",
      "blocks": [
        {
          "type": "section",
          "text": {
            "type": "mrkdwn",
            "text": "*Invoice INV-2041* for *Blue Harbor Logistics* is 15 days overdue.\nBalance due: *SAR 12,450*"
          }
        },
        {
          "type": "actions",
          "elements": [
            {
              "type": "button",
              "text": {
                "type": "plain_text",
                "text": "Send reminder"
              },
              "style": "primary",
              "action_id": "send_reminder",
              "value": "INV-2041"
            },
            {
              "type": "button",
              "text": {
                "type": "plain_text",
                "text": "Open invoice"
              },
              "url": "https://example.com/invoices/INV-2041",
              "action_id": "open_invoice"
            }
          ]
        }
      ]
    }
  ]
}

Related

• Composition objects
• Block Kit overview