Code Syntax Highlighter

Paste code, choose a language, get highlighted HTML for blogs, emails, and documentation.

Code Input
Highlighted Preview
HTML Output
Paste code above to generate highlighted HTML.

How to Use the Syntax Highlighter

  1. Paste your code into the input area or click "Try Example" to load a JavaScript demo.
  2. Select a language — JavaScript, Python, HTML, CSS, SQL, or Auto-detect.
  3. Choose output format — Styled HTML (external CSS), Inline Styled (for emails), or CSS Classes only.
  4. Set theme and line numbers — Dark or Light code theme, optional line numbers.
  5. Copy the HTML from the output panel and paste it into your blog post, email, or documentation.

Output Format Comparison

  • Styled HTML — wraps tokens in <span class="kw"> etc. You must include the CSS classes in your page's stylesheet. Best for CMS blogs and static sites where you control the CSS.
  • Inline Styled HTML — embeds style="color:#cba6f7" directly on each span. No external CSS needed. Best for HTML email newsletters (Gmail, Outlook, Mailchimp).
  • CSS Classes HTML — outputs only the semantic class names (.kw, .str, .num, etc.) without any colors. Write your own stylesheet for full theme control.

Language Token Reference

  • Keywords — language reserved words (if, function, def, SELECT)
  • Strings — single-quoted, double-quoted, and template literals
  • Numbers — integer and floating-point literals
  • Comments — single-line (//, #, --) and multi-line (/* */, )
  • Function names — identifiers immediately followed by (
  • Operators — arithmetic and logical symbols
  • HTML tags and attributes — in HTML mode, tag names and attribute names are coloured separately

Use Cases

  • Blog posts — add syntax-highlighted code snippets to WordPress, Ghost, Substack, or any CMS that accepts raw HTML
  • Email newsletters — use inline-styled output to send code to subscribers via Mailchimp, ConvertKit, or Beehiiv
  • Documentation — embed highlighted examples in Notion, Confluence, or GitBook
  • Slide decks — paste inline-styled HTML into Google Slides or PowerPoint's HTML editor for styled code blocks
  • Stack Overflow answers — copy the HTML to use in answers that accept formatted code

How the Tokenizer Works

This tool uses a regex-based tokenizer that processes code in a single pass. Tokens are matched in priority order: multi-line comments first, then single-line comments, then string literals, then numbers, then function calls, then keywords, then operators. This order ensures that code inside strings and comments is not re-tokenized. The approach is lighter than a full parser but handles the vast majority of real-world code snippets correctly.

Limitations

Regex-based tokenization has edge cases: very complex templates, nested quotes, or unusual Unicode identifiers may not highlight perfectly. For production documentation where precise highlighting matters, consider integrating a full library like Prism.js or Highlight.js. This tool is optimised for quick one-off formatting rather than being a build-time plugin. For more Markdown and code tools, see our Markdown Preview and Diff Checker.

Frequently Asked Questions

The highlighter supports JavaScript, Python, HTML/XML, CSS, and SQL. Select 'Auto' to let the tool guess the language based on patterns in your code.
Styled HTML uses CSS class names (external stylesheet needed). Inline-Styled HTML embeds all colors directly in span tags — ideal for HTML emails. CSS Classes HTML outputs semantic class names only for use with your own stylesheet.
Click the 'Line Numbers: Off' chip to toggle it on. Line numbers use CSS counters so they appear visually but are not selected when you copy the code text.
Yes — use the 'Inline Styled' output mode. Most email clients strip linked stylesheets but preserve inline style attributes. The inline output includes all colors directly in each span tag.
No. The syntax highlighting runs entirely in your browser using a regex-based tokenizer. Your code never leaves your machine — there is no server processing, no logging, and no data collection.