Drop a Markdown 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 a Markdown file right in your browser. Drop a
.md file and you immediately get a clean, rendered
preview plus a small toolkit: a source
formatter, an HTML exporter, a
table of contents, a stats report, and the
raw and hex views. There is no upload and no server — the text is read
directly by your browser, and the rendering 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.
-, one space after each # heading, and long runs of blank lines collapsed. Copy or download the result..html file with its own styling, ready to save or publish. Syntax-highlighted, copy or download.
A Markdown file is untrusted text, and rendering it means turning it into
HTML — exactly where cross-site‑scripting bugs live. OmniViewer’s
renderer escapes every scrap of document text, treats raw or inline HTML in
the source as literal text rather than passing it through, and drops
link and image URLs that use an unsafe scheme (such as
javascript:). So a crafted document renders as words, never as
script.
Markdown was created by John Gruber, with help from Aaron Swartz, in 2004 as a plain‑text writing format that reads naturally and converts cleanly to HTML. Because the original description left corners ambiguous, the community later produced CommonMark, a precise specification, and GitHub’s GitHub Flavored Markdown (GFM) added tables, task lists, strikethrough and autolinks — the flavour most people write today, and the one this viewer renders.
A tiny example of Markdown:
# Title - A **bold** point - A [link](https://omniviewer.org/md)
| Aspect | Markdown | HTML | reStructuredText | AsciiDoc |
|---|---|---|---|---|
| Goal | Readable plain text | Web documents | Technical docs | Technical books & docs |
| Learning curve | Minimal | Moderate | Moderate | Moderate |
| Tables & task lists | Yes (GFM) | Yes | Yes | Yes |
| Standard | CommonMark / GFM | WHATWG living standard | Docutils | AsciiDoc spec |
| First released | 2004 | 1991 | 2002 | 2002 |
OmniViewer opens every file format; Markdown 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 .md file is read directly by your browser, and every tab — preview, formatted, HTML, table of contents 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 preview, formatter, HTML export and stats render the document in memory, so on very large files they work on a bounded prefix and tell you when they do.
It renders CommonMark plus the common GitHub Flavored Markdown (GFM) extensions: headings, bold/italic/strikethrough, inline and fenced code blocks, blockquotes, ordered/unordered and nested lists, task lists, tables, links, images and autolinks. Raw or inline HTML in the source is shown as literal text rather than passed through, for safety.
Yes. The renderer escapes all document text, refuses to pass raw or inline HTML through (it renders as literal text), and drops link or image URLs with unsafe schemes such as javascript:. Combined with the page’s Content-Security-Policy and Trusted Types, a crafted document renders as words and can’t run script or exfiltrate anything.
Yes. The HTML tab gives you the rendered document as a single, self-contained .html file — with its own light/dark styling baked in — that you can copy or download and open anywhere. The Formatted tab, separately, gives you back tidied Markdown source.
Markdown is written to be read as a rendered document, so the preview is the most useful first view. The raw text is always one click away on the RAW tab (with line numbers), and the exact bytes are on the HEX tab — both windowed, so they open a file of any size.
John Gruber created Markdown in 2004, with input from Aaron Swartz, as a plain-text format that reads naturally and converts to HTML. CommonMark later standardised its grammar, and GitHub Flavored Markdown added tables, task lists, strikethrough and autolinks — the flavour most people write today.