Drop an HTML file. Any size.
safe · secure · no server · works offline · fast
…or just start typing at the cursor.
safe · secure · no server · works offline · fast
…or just start typing at the cursor.
OmniViewer opens an HTML file right in your browser. Drop an
.html file and you get a beautified, syntax‑highlighted
view plus a small toolkit: a minifier, an
HTML‑to‑JSON DOM converter, a
stats report, and the raw and hex views. There is no
upload and no server — the markup is read directly by your browser,
and the heavy work runs in a background Web Worker so the page never
freezes. The raw and hex views read only the bytes needed to paint the
screen, so even a huge document opens instantly and privately.
HTML — HyperText Markup Language — was proposed by Tim Berners‑Lee at CERN in 1991 as the document format of the World Wide Web. It is maintained today as a living standard by the WHATWG, having earlier passed through W3C recommendations (HTML 4.01 in 1999, XHTML, and HTML5 in 2014). An HTML document is a tree of nested elements — tags with attributes and text — which is exactly what OmniViewer’s JSON tab makes visible.
A tiny example of HTML:
<a href="https://omniviewer.org/">Open any file</a>
| Aspect | HTML | XML | Markdown | JSON |
|---|---|---|---|---|
| Shape | Nested elements & attributes | Nested elements & attributes | Plain text with light syntax | Nested objects & arrays |
| Primary use | Web documents | Data & documents | Writing prose | APIs & config |
| Strictness | Lenient, error-tolerant | Strict, well-formed | Lenient | Strict |
| Standard | WHATWG living standard | W3C XML | CommonMark | RFC 8259 / ECMA-404 |
OmniViewer opens every file format; HTML is one of the formats with dedicated tooling, powered by the same viewing engine as fastjsonviewer.com and hugecsv.com.
No. OmniViewer is a static page with no server-side processing: your .html file is read directly by your browser, and every tab — formatting, minify, JSON and stats — runs locally in a Web Worker. The file never leaves your computer.
The raw and hex views are windowed — they read only the bytes needed to paint the screen — so they open files of effectively unlimited size, up to 20 GB and beyond; the engine behind them has been tested in-browser with a 40 GB file. The formatted view and the whole-file tools (minify, JSON, stats) transform the file in memory, so on very large files they work on a bounded prefix and tell you when they do.
Formatted beautifies the markup for reading — one element per line, re-indented and syntax-highlighted. Compressed does the opposite: it strips comments and collapses whitespace to minify the file, and reports the before/after size and the percentage saved.
Yes. The JSON tab parses the document into a JSON DOM tree — every element with its attributes and text as nested objects — syntax-highlighted and ready to copy or download. It is a structural conversion of the markup, not a data-scraping tool.
HTML is maintained as a living standard by the WHATWG. Earlier milestones include W3C HTML 4.01 (1999) and HTML5 (2014); XHTML reformulated HTML as strict XML. OmniViewer treats HTML, HTM and XHTML files with the same toolkit.
Tim Berners-Lee proposed HTML at CERN in 1991 as the document format for the World Wide Web. It has evolved through several versions and is now a continuously updated living standard.