Terminalogue

Turn Markdown code blocks into animated terminal sessions. Write commands and sample output as plain text; Terminalogue plays them back in the built-in Markdown preview as if someone were typing at a real terminal.

Write a termlogue fenced code block:

```termlogue
@theme ubuntu
@title Installing Nginx
@prompt user@ubuntu:~$

$ sudo apt install nginx
Reading package lists... Done
Building dependency tree... Done
@wait 800ms
Setting up nginx...
```

…and the preview shows a terminal window in which the command is typed one character at a time, with a little human-looking jitter, followed by its output appearing line by line. The reader can play, pause, restart, pick a playback speed of 1× / 2× / 4× / Instant, and copy the block's commands to the clipboard.

Commands are never executed. Terminalogue is display-only — see Security.

Getting started

Terminalogue extends the built-in Markdown preview; there is no custom preview or webview to open. Install the extension, then press Ctrl+Shift+V (Cmd+Shift+V on macOS) on any Markdown file containing a termlogue block.

Blocks start playing when they first scroll into view, so a long page does not fire off every animation at once.

The DSL

Every line in a termlogue block is one of four things.

Durations are a number followed by ms or s: 800ms, 1.5s. Unknown directives, malformed durations, unknown theme names and unusable sizes produce a diagnostic with a line number, rendered inside the block — a mistake never breaks the preview.

Terminal size

@size 80x24 gives a block a fixed terminal viewport: eighty character columns by twenty-four rows, measured on the terminal body, with the title bar and the controls outside the count. The area is reserved before playback starts, so nothing below the block moves as the session types itself, and output longer than the rows scrolls inside the terminal the way it does in a real one.

Columns run from 20 to 240 and rows from 5 to 100. A terminal never grows wider than the preview pane: when there is not enough room the terminal stops at the pane's width and long lines wrap, and the font is never shrunk to keep the columns. Without @size a block is sized automatically, exactly as before.

Themes

A theme changes colours and nothing else. In particular it does not touch the prompt — @theme powershell still renders a $ unless the block also says @prompt PS C:\Users\Administrator>. All five themes clear WCAG AA contrast, and none of them depends on a platform-specific font, so powershell and cmd render correctly on macOS and Linux too.

Controls

▶  ↻       1×  2×  4×  Instant       Copy

Play/Pause resumes where it left off; Restart plays from the beginning. The speed multiplier divides every delay the document asks for, and Instant drops delays altogether — but it ignores time, not control flow, so @pause still stops playback. Every block on a page has entirely independent state.

Copy puts the block's $ command lines on the clipboard, one per line. Prompts, terminal output and @type input are demonstration material, so none of it is included.

Accessibility

• With prefers-reduced-motion: reduce, nothing autoplays and the finished terminal state is shown immediately.
• The animated screen is aria-hidden; assistive technology reads a separate, complete transcript instead, so typing never produces per-character announcements.
• Every control is a real <button> with an aria-label, reachable by keyboard. The selected speed is marked with aria-pressed, not by colour alone.

Security

Terminalogue never executes anything. A termlogue block is prose that happens to look like a shell session.

• No shell, no child_process, no terminal or task integration. No eval. No network requests — it is entirely client-side and works offline.
• Copy only ever writes a string to the clipboard. It does not read the clipboard, and nothing runs what it copied.
• Block content is never treated as trusted HTML: text reaches the DOM through textContent, so <script>alert(1)</script> renders as literal terminal text.

The extension is enabled in untrusted workspaces and in virtual workspaces, because it only ever renders text.

Also for Obsidian and for Marp

The same parser, renderer and stylesheet ship as an Obsidian plugin and as a Marp CLI engine, so a block looks and animates identically in a Markdown preview, in a note, and on a slide. See the repository.

License

MIT. See LICENSE.