Flash Viewer

Auto-beautify and collapse JSON pages, preview Markdown / CSV / HTML with file drag-in, click the icon to paste and format manually

Flash Viewer makes JSON, Markdown, CSV and HTML content readable right in your browser — with no setup and no data collection. FEATURES • Automatic JSON beautifier Open any raw JSON URL (API responses, config files, docs) and it is instantly rendered as a syntax-highlighted, collapsible tree view. Collapsed nodes show item counts (e.g. "// 4 items"), and scroll position is preserved when you expand them. Regular web pages are never affected. • Markdown & CSV preview Plain-text pages (text/plain, text/csv) are automatically detected and rendered as formatted Markdown or clean CSV tables. Conservative detection means ordinary text pages stay untouched. • Paste & format toolbox Click the toolbar icon to open a live preview editor: paste JSON, Markdown, CSV or HTML on the left, see the formatted result on the right. The format is auto-detected, and the layout (side-by-side or stacked) is adjustable with a draggable splitter. • Drag & drop file preview Drop .json, .md, .csv or .html files directly into the preview panel to view them instantly — the content stays editable. • Privacy-friendly by design All parsing and rendering happens locally in your browser. No network requests, no analytics, no data collection. Markdown and CSV are rendered by a built-in zero-dependency renderer with HTML escaping; HTML previews run in a fully sandboxed iframe with scripts, forms and same-origin access disabled. Perfect for developers inspecting API responses, anyone reading Markdown/CSV files online, or just quickly formatting a chunk of JSON.