Every markdown element, on one page.

Use one # per level with a space before the title. Keep a single H1 per document and don't skip levels — clean heading structure helps readers, HTML conversion, and SEO alike.

Underscores work too (__bold__, _italic_), but asterisks behave more predictably in the middle of words. Strikethrough is a GitHub Flavored Markdown extension.

[Link text](https://example.com "Optional title")
![Alt text](https://example.com/image.png "Optional title")

Auto-linked URL: https://markdownviewer.org

[Reference-style link][1]

[1]: https://example.com

Image syntax is link syntax with a leading !. Bare URLs become clickable automatically in GFM. Always write meaningful alt text — it matters for accessibility and image SEO.

Ordered and unordered lists

1. First item
2. Second item
    1. Indented item
    2. Another indented item

- Apple
- Banana
    - Yellow banana
    - Green banana

Indent nested items with four spaces (or one tab). Ordered lists renumber themselves, so 1. on every line also works.

Task lists (GFM)

- [x] Write the documentation
- [x] Add syntax highlighting
- [ ] Review pull request
- [ ] Deploy to production

Task lists render as checkboxes on GitHub and in this site's Markdown Viewer — where clicking a checkbox updates the markdown source.

> "The best way to predict the future is to invent it." - Alan Kay

> First level
> > Second level
> > > Third level

Prefix each line with >. Stack them for nested quotes, and put other markdown (lists, code, headings) inside freely.

| Feature        | Supported |  Notes       |
|:---------------|:---------:|-------------:|
| GFM Tables     | Yes       | Full support |
| Left aligned   | Yes       | Use :---     |
| Center aligned | Yes       | Use :---:    |
| Right aligned  | Yes       | Use ---:     |

The pipes don't need to line up — renderers only care about structure. Control column alignment with colons in the divider row: :--- left, :---: center, ---: right. Escape a literal pipe inside a cell as \|.

```javascript
function greet(name) {
  const message = `Hello, ${name}!`;
  return message;
}
```

```python
def fibonacci(n):
    a, b = 0, 1
    for _ in range(n):
        yield a
        a, b = b, a + b
```

Fence code with triple backticks and add a language hint (javascript, python, json, rust, sql…) for syntax highlighting — this site's editor recognizes 190+ languages. Use indentation-free fences instead of the old four-space style; they survive copy-paste better.

Inline math: $E = mc^2$ and $\alpha + \beta = \gamma$

Display equations:

$$\frac{\partial f}{\partial x} = \lim_{h \to 0} \frac{f(x+h) - f(x)}{h}$$

$$\sum_{i=1}^{n} i^2 = \frac{n(n+1)(2n+1)}{6}$$

Wrap inline math in single dollar signs and display math in double dollar signs. Common constructs: fractions \frac{a}{b}, roots \sqrt{x}, sums \sum_{i=1}^{n}, integrals \int_a^b, and Greek letters \alpha, \beta. Rendering is powered by KaTeX in this site's Markdown Viewer.

```mermaid
flowchart LR
    A[Start] --> B{Is it working?}
    B -->|Yes| C[Great!]
    B -->|No| D[Debug]
    D --> B
```

```mermaid
sequenceDiagram
    User->>Editor: Type markdown
    Editor->>Preview: Render content
    Preview-->>User: Live preview
```

Mermaid turns text into flowcharts, sequence diagrams, Gantt charts, and more. Write the diagram in a fenced block tagged mermaid — GitHub, GitLab, Notion, and Obsidian all render it natively. Paste the examples into Markdown Viewer to see them rendered with fullscreen zoom and PNG/SVG export.

Markdown allows raw HTML for the few things it has no syntax for. Note that some platforms (like GitHub comments) strip certain tags; the ones above are widely supported.

---

***

___

Three or more hyphens, asterisks, or underscores on their own line all produce a horizontal rule. Leave a blank line above --- so it isn't parsed as a heading underline.

\*Not italic\* and \*\*not bold\*\*

\# Not a heading

\- Not a list item

Put a backslash before a character markdown would otherwise interpret: \* \_ \` \# \[ \] \( \) \| \\.

• GitHub — full GFM plus Mermaid, math, footnotes, and alerts (> [!NOTE]).
• Discord — bold, italic, strikethrough, code, and spoilers (||text||); no tables or headings in normal messages.
• Reddit — basic syntax plus tables and superscript (^text); fenced code blocks work in newer editors.
• Slack — uses its own "mrkdwn": single asterisks for bold, underscores for italic; standard markdown links don't work.

Test any syntax live: open the Markdown Viewer — its built-in sample document contains every example on this page, and you can export the result as HTML or PDF.