Message Formatting

This guide covers Enzyme's message formatting syntax, mentions, links, attachments, and related features.

mrkdwn Syntax #

Enzyme uses mrkdwn, a Slack-compatible markup language for formatting messages.

Inline Formatting #

Unclosed formatting markers are rendered as literal text (e.g., *unclosed stays as *unclosed).

Code Blocks #

Wrap code in triple backticks with an optional language identifier:

```js
const x = 42;
```

Blockquotes #

Prefix lines with >:

> This is a blockquote
> spanning multiple lines

Each line must start with >. Content inside blockquotes supports inline formatting.

Lists #

Bullet lists use • or -:

- First item
- Second item
- Third item

Ordered lists use 1., 2., etc.:

1. First item
2. Second item
3. Third item

List item content supports inline formatting.

Links #

Links use angle bracket syntax with | separating the URL from the display text:

<https://example.com>
<https://example.com|Example>

The first form displays the raw URL. The second displays "Example" as a clickable link. URLs must include a scheme (http:// or https://).

Link Previews #

The first URL in a message automatically generates a link preview.

External links fetch Open Graph metadata (title, description, image) from the target page. Results are cached for 24 hours (1 hour on fetch error). If metadata isn't cached yet, the preview is fetched asynchronously and broadcast to clients via SSE when ready.

Internal message links — URLs matching the pattern /workspaces/{id}/channels/{id}?msg={id} — display an inline preview showing the referenced message's author, content (truncated to 300 characters), timestamp, and channel name. These previews respect access controls: if the viewer doesn't have access to the referenced channel, the content is redacted.

Mentions #

User Mentions #

Syntax: <@userId>

Renders as a clickable blue badge showing @Display Name. Clicking opens a profile popover with a "View profile" button. Triggers a notification for the mentioned user. See Notifications for notification preferences and delivery behavior.

When composing via the API, use the user's ULID (not their display name).

Channel References #

Syntax: <#channelId>

Renders as a clickable badge showing #channel-name with a hashtag icon (or a lock icon for private channels). Clicking opens a popover with the channel description and a "Go to channel" button. If the viewer doesn't have access to the channel, it renders as a generic "private-channel" with a lock icon.

When composing via the API, use the channel's ULID (not its name).

Special Mentions #

These render as highlighted @here, @channel, and @everyone badges.

Emoji #

Shortcodes #

Use :shortcode: syntax to insert emoji (e.g., :smile:, :rocket:, :thumbsup:). Standard shortcodes follow the GitHub gemoji set. Unrecognized shortcodes are rendered as literal text.

Custom Emoji #

Workspaces can upload custom emoji (PNG or GIF, max 256 KB). Custom emoji use the same :shortcode: syntax. Standard emoji take precedence over custom emoji when names conflict.

• Name: alphanumeric characters, hyphens, and underscores (1-63 characters)
• Formats: PNG and GIF only

Large Emoji #

Messages containing only 1-3 emoji (with no other content) render at 4x size.

Character Limit #

Messages have a maximum length of 40,000 characters (counted as UTF-8 runes, not bytes). This limit is enforced server-side when sending, editing, and scheduling messages. Exceeding it returns a 400 response with a validation error.

Attachments #

File Uploads #

• Maximum file size: 10 MB (configurable via files.max_upload_size)
• All file types are accepted
• Multiple files can be attached to a single message

Image Display #

Images (PNG, JPEG, GIF, WebP) display inline with previews. Layout depends on the number of images:

Clicking an image opens a full-screen carousel with arrow key navigation and a download button.

Non-image files display as a list with file name, size, and a download link.

Other Upload Limits #

System Messages #

System messages are generated automatically for channel events. They cannot be edited, deleted, or sent via the API.