Why inline styles instead of CSS classes?

Most places you'd paste this HTML, a wiki, an email, a CMS post editor, don't let you attach a separate stylesheet. Inline `style` attributes on each token mean the highlighted output looks identical wherever it lands, without needing to also copy and register a CSS file alongside it.

Does this validate my YAML first?

No. Highlighting is done with a lightweight tokenizer that recognizes keys, strings, numbers, comments, and the `true`/`false`/`null` keywords by pattern, not a full parser, so it can highlight invalid or partial YAML too, useful when you're highlighting a snippet rather than a complete document. Use the YAML Validator if you need a correctness check.

Can I use this output on a dark or light page?

The generated ` ` block sets its own dark background and light text, so it reads consistently regardless of the surrounding page's theme, the same approach code blocks on documentation sites typically use to avoid clashing with a reader's color scheme.

Is this the same highlighting used elsewhere on this site?

It uses the same token categories, keys, strings, numbers, keywords, and comments, as every other YAML view on this site, so the colors you see in the preview match what you'd see pasting YAML into any other tool here. The HTML output is exported as portable inline styles rather than this site's internal CSS classes.

YAML Syntax Highlighter - Highlight YAML Online

Overview

Introduction

Plain YAML pasted into documentation or a chat message reads as an undifferentiated wall of text. This tool tokenizes YAML into keys, strings, numbers, keywords, and comments, and wraps each in a colored `<span>`, producing HTML you can drop directly into anything that accepts raw HTML.

It's built for portability first: rather than relying on a page's existing CSS or a syntax-highlighting library the reader would need to load, every token carries its own inline color, so the output looks the same everywhere.

What Is YAML Syntax Highlighter?

A YAML syntax highlighter scans text and classifies pieces of it, mapping keys, quoted strings, numbers, `true`/`false`/`null`, and `#` comments, then wraps each recognized piece in a `<span>` with an inline color style.

Unlike a formatter or validator, it doesn't require the input to be a single complete, valid document. It highlights based on lexical patterns, so partial snippets and documents with intentional errors still get colorized.

How YAML Syntax Highlighter Works

A single regular expression scans the input for YAML's core token shapes, keys at the start of a line, comments, quoted strings, numbers, and the boolean/null keywords, and wraps each match in an inline-styled span. Unmatched text passes through as-is, HTML-escaped.

The whole `<pre>` block is generated as one self-contained string, no external stylesheet or script is required to render it correctly wherever it's pasted.

When To Use YAML Syntax Highlighter

Use it when writing documentation, a blog post, or an internal wiki page that includes a YAML example and you want it to read like code, not a plain paragraph.

It's also handy for pasting a config snippet into a tool (an email, a ticketing system) that renders raw HTML but doesn't have its own code-block support.

Often used alongside YAML Formatter & Prettifier and YAML Validator.

Features

Advantages

Produces portable HTML with inline styles, no external CSS dependency.
Highlights partial or intentionally invalid snippets, not just complete valid documents.
Runs entirely client-side.
Live preview shows exactly what the copied HTML will look like.

Limitations

This is a lexical highlighter, not a parser, so it doesn't validate the YAML or catch structural errors.
Complex multi-line block scalars (`|` and `>`) are highlighted as plain text rather than as a distinct token type.
Colors are fixed and not currently configurable.

Examples

Basic mapping with a comment

Input

# service config
name: api
replicas: 3

Output

<pre>...<span style="color:#94a3b8"># service config</span>\n<span style="color:#38bdf8">name</span>: api\n<span style="color:#38bdf8">replicas</span>: <span style="color:#fbbf24">3</span>...</pre>

Comments, keys, and numbers each get their own inline color, wrapped in a self-contained <pre> block.

Best Practices & Notes

Best Practices

Preview the output before copying it, since some CMS editors strip inline styles from pasted HTML.
Keep snippets focused; a highlighted 200-line manifest is rarely more readable than a shorter, relevant excerpt.
Use the YAML Validator first if you need to confirm correctness, since this tool won't catch structural errors.

Developer Notes

The tokenizer is a single `g`-flagged regex with five capture groups, one per token category, matched with `String.matchAll()`. Text between matches is HTML-escaped and passed through unchanged. Each matched token is wrapped in `<span style="color:...">`, with the color values chosen to match the same token palette used elsewhere on this site, so a YAML snippet looks the same whether it's viewed in another tool's live preview or exported as standalone HTML here.

YAML Syntax Highlighter Use Cases

Embedding a colorized YAML example in a blog post or documentation page
Pasting a highlighted config snippet into a ticket or support email
Producing a code-block-style YAML example for a tool without native syntax highlighting

Common Mistakes

Pasting the copied HTML into an editor that strips inline styles, then wondering why the colors disappeared.
Assuming a successful highlight means the YAML is valid, when highlighting works on invalid input too.

Tips

Check the live preview before copying, it's exactly what the exported HTML renders as.
For a real correctness check, run the same input through the YAML Validator first.

YAML Syntax Highlighter