Slack mrkdwn

Slack's custom text formatting syntax for messages and text objects. Not standard Markdown.

CRITICAL: Two Markup Systems

Slack has two completely different markup syntaxes. Using the wrong one is the most common formatting mistake.

text

type: "mrkdwn"

*bold*

<url|text>

markdown

**bold**

[text](url)

# Heading

Standard Markdown syntax (

**bold**

[text](url)

# Heading

*bold*

<url|text>

The

markdown

type: "markdown"

markdown

mrkdwn Syntax

*bold*

**bold**

_italic_

*italic*

~strikethrough~

~~strikethrough~~

`code`

```code```

> quoted text

<https://example.com|display text>

[text](url)

:emoji_name:

\n

1. item

- item

rich_text

Inline code disables all other formatting within it — use it to display literal text like

*not bold*

Nested Formatting

Combining adjacent format markers without spaces (e.g.,

*bold*_italic_

*bold* _italic_              ← works reliably
*bold*_italic_               ← may fail to render

For reliable combined formatting on a single word, use

rich_text

{"bold": true, "italic": true}

Links

<https://example.com>                            Auto-detected URL
<https://example.com|Display Text>               URL with custom text
<mailto:user@example.com|Email Link>             Email link

URLs posted in text are auto-linked by Slack. Use

<url|text>

<url|*bold*>

Link Unfurling

Slack previews ("unfurls") linked content. Control this per message:

unfurl_links

false

unfurl_media

true

Set both to

false

chat.postMessage

Mentions and References

User Mentions

<@U0123ABC456>

Triggers a notification for the mentioned user. Auto-converts to display name.

Channel References

<#C0123ABC456>

Auto-converts to channel name. Users without access see "private channel".

User Group Mentions

<!subteam^SAZ94GDB8>

Notifies all members of the user group.

Special Mentions

<!here>

<!channel>

<!everyone>

Best Practice

Always use IDs, not names. IDs are stable; names change:

  <@U0123ABC456>       (user ID)
  @chris                (name — may not resolve)

  <#C0123ABC456>       (channel ID)
  #general              (name — may not resolve)

To enable name-based parsing, set

link_names: 1

Date Formatting

Displays dates/times localized to the reader's device timezone (not their Slack preference timezone).

Syntax

<!date^{unix_timestamp}^{token_string}^{optional_link}|{fallback_text}>

Tokens

{date_num}

{date}

{date_short}

{date_long}

{date_pretty}

{date_short_pretty}

{date_long_pretty}

{time}

{time_secs}

{ago}

_pretty

Examples

<!date^1392734382^{date} at {time}|February 18th, 2014 at 6:39 AM PST>
<!date^1392734382^{date_short_pretty} {time}|Feb 18, 2014 6:39 AM>
<!date^1392734382^{ago}|February 18th, 2014>

Tokens can be mixed with literal text in the token string. The optional link (third

^

|

Escaping

Only three characters require escaping in mrkdwn:

&

&

<

<

>

>

Do NOT encode other characters as HTML entities. Only these three are control characters in Slack's markup system.

When displaying user-generated content that may contain these characters, always escape them to prevent unintended formatting or link injection.

Text Object

The text object is the most common composition object in Block Kit. It determines how text is rendered.

{ "type": "mrkdwn", "text": "*bold* and _italic_", "verbatim": false }
{ "type": "plain_text", "text": "No formatting", "emoji": true }

mrkdwn

plain_text

emoji: true

:emoji:

fields

Where Each Type Is Allowed

plain_text

mrkdwn

plain_text

mrkdwn

plain_text

plain_text

plain_text

plain_text

plain_text

plain_text

mrkdwn

plain_text

Verbatim Behavior

When

verbatim: false

• URLs auto-convert to clickable links
• Channel names auto-convert to channel links
• Mentions auto-parse

When

verbatim: true

• Markdown formatting still processes
• No auto-linking or mention parsing
• Useful for displaying raw URLs or text containing

  @

  or

  #

  that aren't mentions

{ "type": "mrkdwn", "text": "Check the log at http://example.com/debug", "verbatim": true }

Auto-Parsing Behavior

The

parse

Parameter (chat.postMessage)

"none"

"full"

Disabling Auto-Parsing

In text objects: Set

verbatim: true

In message payloads:

• Omit

  link_names

  argument (or set to

  0

  )
• Set

  parse: "none"

  to disable all auto-parsing

Disabling Formatting Entirely

type

"plain_text"

text

mrkdwn: false

mrkdwn_in

Anti-Patterns

**bold**

*bold*

[text](url)

<url|text>

# Heading

header

markdown

*bold*

**bold**

link_names: 1

<@USERID>

&<>

&

<

>

%20

*bold*_italic_

*bold* _italic_

Secondary Attachments (Legacy)

The

attachments

fallback

text

blocks

fallback

color

"good"

"warning"

"danger"

pretext

author_name

author_link

author_icon

title

title_link

text

fields

{ title, value, short }

image_url

thumb_url

footer

footer_icon

ts

mrkdwn_in

"text"

"pretext"

"fields"

Only

"text"

"pretext"

"fields"

mrkdwn_in

fallback

Prefer Block Kit blocks over attachments for new development.

Reference Documentation

Sources

• Formatting Message Text — Slack
• Block Kit Composition Objects — Text Object — Slack
• Markdown Block — Slack
• Legacy Secondary Message Attachments — Slack
• Messaging Overview — Slack