Online File Viewer

What is Online File Viewer?

Online File Viewer is a free, browser-based viewer for the files you most often need to read but not edit: Excel spreadsheets, CSV, JSON, YAML, Markdown and HTML. Paste your text or drop a file and it detects the format automatically — spreadsheets become a sortable table, JSON becomes a collapsible tree you can format or minify, Markdown renders as formatted text, and HTML previews safely in a sandbox. You can open several files at once: each one gets its own tab, so you can switch between a spreadsheet, a config file and a README without losing your place. A document in a language you do not read can be translated in place with Google Translate — the only feature that sends anything anywhere, and only when you ask for it. Everything else runs locally in your browser, so nothing is uploaded to a server and the tool keeps working offline.

How to use Online File Viewer

1. Paste your text into the box, or drop a file anywhere on the page (you can also click Open files in the tab bar).
2. The format is detected automatically — CSV, JSON, YAML, Markdown or HTML — and the preview appears instantly.
3. Open more files — select several at once, or drop them together — and each one appears as its own tab above the editor. Click a tab to switch, or press Ctrl/Cmd+1 to Ctrl/Cmd+9.
4. Use the Auto / Markdown / CSV / JSON / HTML / YAML buttons if you want to force a specific format.
5. Sort CSV columns, filter rows, search JSON keys, format or sort JSON and YAML — then copy, download, or share the document as a link.
6. To read a document written in another language, open the Translate menu above the preview and pick one of 43 languages — the preview is translated in place, and the language chip beside it flips back to the original.

Open several files at once — one tab each

Comparing two exports, or reading a config next to the README that explains it, should not mean opening the tool twice. Select several files in the Open dialog — or drop a whole handful onto the page — and each one opens in its own tab above the editor, named after the file. Every tab keeps its own text, its own detected format and its own Excel sheet selection, so switching back and forth costs nothing. Click a tab to switch, press Ctrl/Cmd+1 through Ctrl/Cmd+9 to jump straight to one (9 is always the last tab), Alt/Option+T for a new empty tab and Alt/Option+W to close the current one; the middle mouse button closes a tab the way it does in a browser. Drag tabs to reorder them, double-click a tab to rename it, and every open tab is restored the next time you come back to the page.

CSV viewer — read spreadsheets without a spreadsheet

Paste or drop a .csv or .tsv file and it becomes a clean, readable table with a sticky header row. Commas, semicolons and tabs are all detected automatically, and quoted fields containing commas or line breaks are parsed correctly. Click any column heading to sort the rows — numbers sort as numbers, text sorts alphabetically, and clicking again reverses the order. It is the fastest way to check an export without opening Excel, Numbers or Google Sheets.

JSON viewer — a readable, collapsible tree

Paste minified or badly formatted JSON and it becomes an indented, colour-coded tree you can actually read. Objects and arrays collapse and expand so you can drill into a deeply nested API response without scrolling past thousands of lines, and each branch shows how many keys or items it contains. If the JSON is invalid, you get the error message and the line number where parsing failed — a quick way to find a stray comma or missing bracket.

Markdown viewer with live preview

Paste Markdown and see it rendered as you type, side by side with the source, with two-way synchronised scrolling. Headings, bold and italic, links, images, blockquotes, nested bullet and numbered lists, task lists, GitHub-flavoured tables with column alignment, inline code and fenced code blocks are all supported, and YAML front matter is recognised and hidden. It is handy for previewing a README, checking formatting before you commit, or simply reading a .md file that your editor shows as plain text.

Mermaid diagrams, LaTeX math and syntax highlighting

Fenced mermaid blocks are drawn as real diagrams — flowcharts, sequence diagrams, class and state diagrams, Gantt charts and more — and LaTeX written between $$ delimiters is typeset as proper mathematical notation. Code blocks are syntax highlighted for JavaScript, Python, HTML, SQL, shell and other common languages. The diagram and maths engines are self-hosted rather than pulled from a third-party CDN, and they are downloaded only when a document actually contains a diagram or a formula, so an ordinary Markdown or CSV file still loads in a few kilobytes.

Rich HTML inside Markdown

Real-world Markdown often falls back to HTML for things the syntax cannot express, and this viewer renders it: multi-row table headers using rowspan and colspan, keyboard keys with the kbd tag, highlighted text, underlines, superscript and subscript for formulas like H₂O and x², abbreviations with hover tooltips, centred or right-aligned blocks, and images with explicit dimensions. Everything passes through a strict allowlist first — scripts, event handlers, iframes, forms and unsafe URLs are stripped — so you can safely paste a document from anywhere.

JSON formatter — beautify or minify in one click

Paste minified JSON and press Format to pretty-print it with two-space indentation, or press Minify to strip every unnecessary character before shipping it. The formatter uses your browser’s native JSON engine, so output is always standards-exact, and because it rewrites the text in the editor you can copy the result straight back out or download it as a .json file. Validation is built in: if the input is not valid JSON you get the error and line number instead of a silent failure.

HTML viewer with a safe sandboxed preview

Paste an HTML file — or drop a .html, .htm or .svg file — and see it rendered as a real page. The preview runs inside a fully sandboxed frame: styles, layout, images and inline SVG all work, but scripts, forms, popups and navigation are blocked by the browser’s sandbox, so viewing an email template or a page you do not trust cannot execute any code. It is a quick way to check a saved page, an HTML email, or a generated report without opening it live.

Excel viewer — open .xlsx without Excel

Drop an .xlsx, .xls or .ods workbook and it opens as a clean, sortable table — no Microsoft Office, no Google account, no upload. Multi-sheet workbooks show a sheet switcher, and every table feature works on spreadsheet data: click a column to sort, filter rows as you type, read the per-column statistics, and export the result as CSV. The spreadsheet engine is self-hosted and downloaded only when you actually open an Excel file, and like everything else it runs entirely in your browser — safe for payroll exports, client data and anything else you would not upload to a random website.

Column statistics and smart tables

Tables think along with you. Columns are type-detected — numbers align right with tabular figures — and a statistics row under every table shows the sum, average and range of each numeric column and the distinct-value count of each text column, recalculated live as you filter. JSON and YAML arrays of records get a Table button that turns an API response into the same sortable, filterable grid, exportable as CSV.

YAML viewer and validator

Paste a YAML file — a Kubernetes manifest, a CI pipeline, a docker-compose file or any config — and it renders as the same collapsible tree as JSON, with validation built in: syntax errors report the line number. The Format button re-emits clean, consistently indented YAML, and Sort A–Z alphabetises the keys. The YAML engine is self-hosted and loaded only when a YAML document is detected.

Search, filter and share

A filter box searches as you type: in a CSV it hides non-matching rows and shows “42 of 10,000 rows”, and in JSON or YAML it highlights matching keys and values and expands the branches that contain them. Very large tables render the first 2,000 rows instantly with one click to show the rest. When you want a colleague to see the same document, Share compresses it into the link itself — the data lives in the URL fragment, which browsers never send to any server, so even shared documents stay private.

Translate a file into another language

A supplier sends a spreadsheet in Spanish, a config file arrives commented in German, a README is written in Japanese. Open the Translate menu above the preview, pick one of 43 languages, and the document is translated in place with Google Translate — no copy-pasting into another tab, and no losing the file’s shape. A CSV keeps every column and row, and numbers and dates are left alone; JSON keeps its keys, its structure and its URLs and only the string values change; YAML keeps its keys, comments and indentation; Markdown keeps its headings, tables, links and lists, and code inside fenced blocks is never touched. Because the translation is rebuilt as a real document rather than as patched-up text, everything else still works on it: sort the translated table, filter it, expand the tree, copy it or export it as CSV, JSON or PDF. Your editor keeps the original the whole time, and the language chip beside it flips between the two.

Private by design — nothing is uploaded

This viewer has no server component. Files you open are read by your own browser with the File API and rendered locally, so nothing is ever transmitted, stored or logged, and there is no tracking code, no analytics and no cookies. That makes it safe for client exports, database dumps, API responses and anything else you would not want to hand to a random website. Once the page has loaded it also works with no internet connection at all. The single exception is the optional Translate button: choosing a language sends that document’s text to Google Translate, because translation cannot happen offline. Nothing is sent until you pick a language, the menu says so before you do, and if you never use it nothing ever leaves your browser — so keep confidential files untranslated.

Who uses Online File Viewer?

• Developers — inspect an API response or a config file without leaving the browser.
• Analysts — peek at a CSV export before importing it into a spreadsheet or database.
• Writers & documentation authors — preview a README or Markdown draft exactly as it will render.
• Support & ops teams — open a log dump or data export on a machine with nothing installed.
• Anyone on a locked-down or borrowed computer — read a file with no software to install and no account to create.

Frequently asked questions