Features

Loading and rendering

• Lazy ZIP: reads only the central directory, inflates each part on demand (native DecompressionStream, 0 dependencies)
• HTTP Range: open a URL → fetch only the bytes needed (256 KB block cache); server without Range support → automatic full-download fallback
• Streaming XML parser runs in a Web Worker → UI never blocks
• Progressive render:
  • DOCX: blocks (paragraph/table) stream in → offscreen height measurement in time slices → pagination → only visible pages render
  • XLSX: rows stream in, 2D virtualized grid (only cells in viewport render), freeze panes, merge, number format, sheet tabs
  • PPTX: slides parsed on demand when scrolled into view, virtualized thumbnails

Format support

.doc/.xls/.ppt (legacy binary) and encrypted files are not supported.

Editing

DOCX

• Typing: type/delete/Enter, paste (keeps formatting when pasting from Word/Google Docs/web), IME input (e.g. Vietnamese)
• Text formatting: B/I/U/S, superscript/subscript, font, size, color, highlight, paint format
• Styles: Normal, Title, Subtitle, Heading 1–6 always available (created in the file when missing; Ctrl/⌘+Alt+0…6), document outline panel
• Paragraphs: alignment, line spacing, bullet/number list, indent, page break
• Images: insert (file picker/paste/drag & drop), click to select with 8 resize handles, original size, fit width, replace, alt text, download
• Tables: insert, add/delete rows & columns, delete table, Tab between cells
• Other: link (dialog), special characters, right-click context menu (clipboard, link, table, image, insert), find & replace, word count, undo/redo

XLSX

• Cells: edit, range selection, copy/cut/paste, fill down/right, sort, find & replace (match case, entire cell, in formulas)
• Formulas: auto-calculated (134 functions), function name & argument hints while typing, click/drag cells (incl. other sheets, arrow keys) to insert references, colored references, auto-close parentheses, functions menu (SUM/AVERAGE/COUNT/MAX/MIN)
• Formatting: paint format, currency/percent/decimal buttons + 20 number formats, font, size, B/I/U/S, text/fill color, borders (8 kinds, color, line style), merge all/horizontally/vertically, horizontal & vertical alignment, wrap, text rotation, clear formatting
• Rows & columns: insert/delete/hide/unhide, drag to resize column width/row height, freeze, gridlines
• Sheets: add/rename/delete/reorder
• Other: context menu, undo/redo

PPTX

• Text: font, size, B/I/U/S, color, highlight, superscript/subscript, alignment, vertical alignment, line spacing, bullet/numbered list, indent level, clear formatting
• Shapes: select/drag/resize/delete (arrow keys to nudge), fill, border color/weight/dash, arrange (front/forward/backward/back), rotate 90°/flip, align on slide, duplicate (⌘D), undo/redo
• Insert: 30 shapes, text box, image
• Slides: background, add/duplicate/delete/move/hide, slideshow from current slide or beginning
• Other: context menus on shapes/slides/thumbnails

Toolbar

Single row, buttons that don't fit collapse into ⋮; custom-drawn dropdowns (font/style preview, number formats with examples, ↑↓/Enter/Esc/type-ahead keys, never steals focus from the document); font size box − 11 + accepts direct input; cell borders picked from an icon grid; color pickers have a palette plus a Custom row (+ opens the system color picker, recent custom colors are remembered across sessions).

File menu

• New: blank document, spreadsheet or presentation (16:9, Office theme, title / content / blank layouts)
• Open (Ctrl/⌘+O): .docx .xlsx .pptx open as they are; .csv / .tsv become a workbook (numbers and booleans typed, codes like 007 kept as text); .txt / .md / .html become a document (headings, lists, bold / italic / strike, links, code)
• Download as: the native format, PDF, web page (.html, images embedded), plain text / Markdown (DOCX), CSV / TSV of the current sheet (XLSX), slide text with notes (PPTX)
• Import CSV into new sheet (XLSX): adds a sheet after the current one with the file's rows
• Save (Ctrl/⌘+S), Rename (shown name and the name used for saving), Document details (file, core properties, page / word / slide counts)
• Host entries (fileMenuItems: Share, Version history…) and Close (onClose)
• PDF / Print (Ctrl/⌘+P): rendered off-screen and sent to the browser print dialog (choose "Save as PDF"): DOCX pages as paginated on screen, PPTX one slide per page, XLSX current sheet fitted to the paper width

Saving

• DOCX: edited paragraphs are regenerated from the original XML (keeps pPr, rPr, images, bookmarks, comments); untouched paragraphs keep original bytes
• XLSX: only <row>s containing edited cells are rewritten (streamed, never loads the whole sheet into a DOM); new strings written as inline strings; fullCalcOnLoad set so Excel recalculates formulas
• PPTX: only a:p of edited shapes are regenerated
• Unchanged ZIP entries are copied as-is (no recompression)

Limitations

• Formulas: no defined names, structured refs (Table1[Col]), 3-D refs
• DOCX: header/footer, text boxes and nested tables are read-only; paragraphs with fields spanning multiple paragraphs (TOC) are read-only; "update style to match selection" is not available
• XLSX: no chart/pivot/conditional format/data validation/filter editing; inserting/deleting rows & columns doesn't shift conditional formats/data validation
• PPTX: can't rotate shapes with the mouse yet, can't edit text inside tables yet, no table insert, no animations/transitions; slide list changes (add/delete/move) are not undoable