What does the HTML Formatter and Minifier do?
Use this tool when you need a browser utility that parses HTML and either prints readable markup or removes comments and unnecessary whitespace for delivery. It accepts one HTML document or fragment up to 2 MB and returns Prettier-formatted HTML or conservatively minified HTML. Results are deterministic for the same input except where cryptographic randomness, current time, or a live provider response is part of the task.
Format, minify, and sanitize are different jobs
Use formatting for maintenance and review. Use minification only for a tested delivery artifact. Use a dedicated sanitizer when markup comes from an untrusted source; neither formatting nor minification makes HTML safe to render.
How do you use it?
- Choose Format HTML for readable markup or Minify HTML for a compact delivery copy.
- Paste an HTML document or fragment no larger than 2 MB into Input and select Convert.
- Review the output, especially whitespace-sensitive text and embedded code, then copy it or download html-output.html.
Worked example
Format and minify a compact document fragment
Input
<main><h1>KitLumi</h1><!-- remove --><p>Local tools</p></main>Output
<main>
<h1>KitLumi</h1>
<!-- remove -->
<p>Local tools</p>
</main>
Minified: <main><h1>KitLumi</h1><p>Local tools</p></main>Format mode preserves the comment and lays out the markup. Minify mode removes the comment and collapses optional whitespace while retaining explicit tags and quoted attributes.
Common errors and fixes
| Symptom | Likely cause | Fix |
|---|---|---|
| The formatted structure is not the structure you expected. | HTML parsing is error-tolerant, so a missing closing tag or invalid nesting can be repaired according to HTML parsing rules. | Correct incomplete or misnested markup before treating the formatted result as an authoritative source. |
| The minified page behaves or renders differently. | Whitespace can be significant in inline content, preformatted text, templates, or code that reads exact text nodes. | Regression-test the output in its real template and browser context; keep the formatted source when whitespace semantics are uncertain. |
| Dangerous markup is still present after minification. | A minifier reduces source size; it does not sanitize scripts, event handlers, URLs, or embedded content. | Use a dedicated allowlist-based HTML sanitizer before rendering any untrusted HTML. |
Important behavior of HTML Formatter
Minification is not sanitization: scripts, event handlers, unsafe URLs, and other active content remain in the output and must still be treated as untrusted.
Standards and implementation references
- Prettier browser documentation (opens in a new tab)Documents the standalone browser formatter and explicit HTML parser plugin used by Format HTML.
- html-minifier-terser official repository (opens in a new tab)Documents the HTML minification options and browser distributions used by Minify HTML.
- WHATWG HTML Standard (opens in a new tab)Defines HTML parsing, document structure, and whitespace behavior.
Frequently asked questions about HTML Formatter
Does the HTML Formatter upload my input?
No. Processing runs in the current browser tab, and the page does not send tool input to a KitLumi processing endpoint.
What input does the HTML Formatter accept?
It accepts one HTML document or fragment up to 2 MB. The workspace checks the input and reports malformed or unsupported values before it produces a result.
What does the HTML Formatter produce?
It produces Prettier-formatted HTML or conservatively minified HTML. Copy and download controls appear when the output format supports them.
What limitation should I know?
Minification is not sanitization: scripts, event handlers, unsafe URLs, and other active content remain in the output and must still be treated as untrusted.
What changed?
Added Prettier HTML formatting, Conservative HTML minification, Inline code left unchanged, Local HTML download, responsive controls, explicit runtime disclosure, and task-specific examples and limitations.