Message Syntax

Send message bodies as text through the Chatto API. Keep the source unchanged when you edit, quote, or copy messages. A client that does not support a visual renderer can show the source code.

Supported Markdown

Message bodies support paragraphs, ATX headings, bold, italic, underline, links, inline and fenced code, blockquotes, lists, footnotes, and GFM pipe tables. Use **bold**, *italic*, and __underline__. Double underscores mean underline, including in existing messages. Code spans and code blocks keep their literal text.

Timestamp tokens such as <t:UNIX_SECONDS:F> identify a UTC instant. Clients show valid tokens in the reader’s locale and time zone. Clients without timestamp support can show the token unchanged.

Emoji shortcodes such as :wave: and :+1: remain in the source and render as Unicode emoji. Names are case-sensitive. Unknown names stay as text. Separate shortcodes from letters, numbers, combining marks, and literal underscores. Code blocks, inline code, and URLs do not expand shortcodes.

Visual code blocks

Use mermaid, svg, or ansi as a code-fence language. Add rendered after the language to request a visual presentation first. Rendering runs locally; Chatto does not send the code to an external rendering service.

Mermaid diagrams

```mermaid rendered
flowchart LR
  accTitle: Delivery status
  accDescr: A parcel moves from packing to shipping to delivery.
  A[Packed] --> B[Shipped] --> C[Delivered]
```

Mermaid diagrams use Pele. Links, external images, and source configuration are disabled. Each message can render up to four diagrams with at most 10,000 characters each. Invalid, unsupported, or overly complex diagrams show source. Add accTitle and accDescr for screen readers.

SVG previews

```svg rendered
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 120 60">
  <rect width="120" height="60" rx="12" fill="#257d68"/>
  <text x="60" y="36" text-anchor="middle" fill="white">Ready</text>
</svg>
```

SVG previews use isolated images. Include the SVG namespace. Scripts, links, external resources, CSS, embedded images, filters, patterns, masks, clipping paths, markers, and use references are removed. Simple animate and animateTransform elements are supported; CSS animations, motion paths, and event-based timing are not. Durations must be from 100ms to 3600s.

Each message can render up to four SVG previews, each with at most 100,000 source characters, 1,000 elements, and 32 element levels including the root. DTD and entity declarations are rejected. Unsupported or larger blocks show source. The source message stays unchanged; image downloads contain the sanitized SVG.

ANSI art

Use an ansi rendered fence. Send an actual Escape character (U+001B) in ANSI sequences, rather than the literal text \x1b. For example, in JavaScript:

const body = '```ansi rendered\n\x1b[91mHello in red!\x1b[0m\n```';

The renderer supports 16-color, 256-color, and true-color text on an 80-column screen with up to 100 rows and no scrollback. It does not play animations or execute terminal links or clipboard commands. The first four ANSI blocks render; additional blocks show source. Use Unicode for box-drawing characters.

Prevent a link preview

Put a complete HTTP or HTTPS URL in angle brackets:

<https://example.com>

The URL stays clickable without a preview attachment. A later URL outside angle brackets can still produce a preview. Omitting the closing angle bracket also suppresses the preview.

Links

Automatic links start with www., https://, or http://. Bare domains, filenames, and email addresses stay as text. Use an explicit Markdown link or mailto: when needed. Message links permit HTTP, HTTPS, and mailto:. Explicit Markdown links can also use a path that starts with one / on the current origin.