Markdown Preview

A Markdown workspace that runs entirely in your browser. Write in a real code editor on one side and read the rendered document on the other, GitHub-style: headings, lists, task lists, tables, fenced code with syntax highlighting, footnotes, > [!NOTE] alerts, YAML front matter, maths written in LaTeX and Mermaid diagrams. Keep many documents in tabs and folders; they are saved in this browser as you type, with a trash and up to twenty snapshots per document to go back to. An outline, a lint panel and a list of every link and image help you tidy a long README or a set of docs, and you can export a .md file, a standalone HTML page, a PDF through your browser’s print dialog, or the whole workspace as a ZIP.

1. Write in the editor, or press Open (Ctrl/⌘+O) or drop .md files anywhere on the workspace. Several files open in tabs at once.
2. Choose Write, Split or Read above the editor. In Split, drag the bar between the panes; the two sides scroll together.
3. Format with the toolbar or the keys — Ctrl/⌘+B bold, Ctrl/⌘+I italic, Ctrl/⌘+K link, Ctrl/⌘+Alt+1 to 6 headings — or press Ctrl/⌘+Shift+P for every command by name.
4. Bring text in with Insert → Paste as Markdown (from a web page, Word or Google Docs) or Table from CSV, TSV or JSON; Insert → Tidy the document evens out the style in one step you can undo.
5. Open the panel on the right for the outline, problems (skipped heading levels, broken #links, images without alt text, unclosed code blocks), links and snapshots.
6. Save with Ctrl/⌘+S. In Chrome and Edge the browser can save straight back to the file you opened, after it asks you; elsewhere it downloads a copy. Export also makes HTML, PDF, a ZIP of the workspace or a backup file.

• Raw HTML in a document is shown made safe: kept tags include details, kbd, sub and sup, tables and images embedded as data:; scripts, styles, frames, forms and event handlers are removed. Settings can show it as text instead.
• Images from other websites are shown as a note with their address, never fetched. Links open only web, email and phone addresses, in a new tab without a referrer. Links to other sites are not checked, as that would send each address to its site.
• Files up to 50 MB open; above 5 MB you are asked first, and the preview catches up a moment after you pause typing. Files must be UTF-8 or UTF-16 text. A UTF-8 byte-order mark is not kept, and a file mixing CRLF and LF line endings is saved with the one it uses most.
• Maths, diagrams and each code language’s highlighting download the first time they are used, then work offline. The editor itself does too: offline on a device that never opened it, a plain text box stands in until the connection returns.
• PNG export of a whole document, share links, live collaboration, cloud sync and GitHub import are not offered: the first would cut long documents off without saying so, the rest need a server and would take your documents off this device.
• Everything happens on this device: editing, the preview, maths, diagrams, search, lint, snapshots and every export. No document or file name is sent anywhere, and there are no analytics or third-party scripts on this site. Documents are kept in this browser’s IndexedDB, not encrypted — anyone using this browser profile could read them — so on a shared computer turn on a private session in Settings, which keeps nothing once the tab closes. Images from other websites are never loaded, so a tracking pixel in a document cannot tell anyone you opened it. Your documents are included in “Export my data” and removed by “Delete everything”.

In this browser, on this device, in its IndexedDB storage for toolsdev.in. They stay until you delete them or clear the site’s data. Make a backup (Export → Backup file) to move them to another browser, or download them as a ZIP of .md files.

It follows GitHub-flavoured Markdown for headings, emphasis, lists, task lists, tables, code blocks, autolinks and strikethrough, and adds GitHub’s alerts, footnotes, $maths$ and ```mermaid diagrams. Heading ids follow GitHub’s rules, so #section links match. GitHub-only features such as @mentions and emoji shortcodes stay as text.

Put inline maths between single dollars — $E = mc^2$ — and display maths between $$ lines. For a diagram, fence it as ```mermaid with any Mermaid diagram inside: flowcharts, sequence, class, state, ER, Gantt and more. Both are drawn on your device.

A deleted document goes to the trash at the bottom of the documents list until you empty it. For changes, the History panel keeps snapshots — save one any time; one is also taken before a restore and when you open a document after a day away. Pick a snapshot to see what changed and restore it; Ctrl/⌘+Z undoes the restore.

Use Table on the toolbar, or write a header row with cells separated by |, a row of dashes, then the data rows. A colon on the right of the dashes aligns that column right, on both sides centres it. With the cursor in a table, Insert → Line up the table (Ctrl/⌘+Alt+F) pads the columns, and the same menu adds or deletes rows and columns.