Excel Viewer & Converter

What is Excel Viewer & Converter?

An Excel viewer and converter lets you open and inspect XLSX, XLS, and CSV spreadsheet files directly in your browser without Microsoft Excel or any office software. This tool parses spreadsheet data, displays it in an interactive table, and converts it to universally-readable formats like JSON (for developers) and CSV (for spreadsheets and databases). All processing happens entirely within your browser — your files never leave your device.

Spreadsheets are the lingua franca of business data. Whether you received an .xlsx attachment you cannot open on your phone, need to inspect CSV export data, or want to convert a workbook table to JSON for an API integration, this tool eliminates the need for expensive software installations.

Why This Beats AI

Large language models (ChatGPT, Claude, Gemini) have critical failures when handling spreadsheet files:

1. Cannot read binary files — AI models cannot open .xlsx or .xls binary files at all. They have no file system access and cannot parse ZIP-compressed XML workbooks (which is what .xlsx actually is).
2. Hallucinated data — When shown a screenshot of spreadsheet data, AI invents rows, merges cells incorrectly, and fabricates values. A 50-row sheet becomes 53 or 47 rows.
3. Type corruption — Numbers with many digits (like IDs: 1000000000001) lose precision. Dates are misformatted. Currency values get rounding errors.
4. Multi-sheet failure — AI cannot handle workbooks with multiple sheets. You must manually copy-paste each sheet's data individually.
5. Large file limits — AI context windows are typically 32K-200K tokens. A 1MB Excel file with 5000 rows is far beyond what any LLM can process, but this tool handles files up to browser memory limits.

This tool uses the battle-tested SheetJS library for deterministic binary parsing with zero hallucination risk. Every cell is read, every value is preserved, and every sheet is accessible.

Features

• Multi-format support — Open .xlsx, .xls, and .csv files in one tool
• Sheet navigation — Switch between sheets in multi-sheet workbooks with easy tab buttons
• Convert to JSON — Export spreadsheet data as clean JSON (array of objects, array of arrays, or keyed by column)
• Convert to CSV — Export any sheet as comma, semicolon, tab, or pipe-delimited CSV
• Copy & download — Copy converted data to clipboard or download as a file
• Drag-drop upload — Drag files directly onto the drop zone or click to browse
• File info — See file name, size, and sheet count at a glance
• 100% client-side — Zero upload, zero server, zero API keys needed

Common Use Cases

• No Excel installed — Open an .xlsx attachment from email without buying Microsoft Office
• Data extraction — Extract table data from Excel files for use in databases or code
• API integration — Convert Excel data to JSON format for feeding into REST APIs or web applications
• Data migration — Convert between Excel and CSV when switching between spreadsheet tools
• Quick inspection — Preview the contents of an unknown .xlsx file before deciding how to process it

How It Works

When you drop or select a file, the SheetJS library (xlsx.js) reads the binary file in your browser using a JavaScript implementation of the Open XML standard. It decompresses the ZIP archive (for .xlsx files), parses the XML workbook and sheet data, and converts all cells into a JavaScript data structure. The tool then renders the data as an HTML table and makes it available for conversion to JSON or CSV. Because everything happens in your browser, there are no privacy concerns, no file size limits beyond available memory, and no network latency.

Excel vs CSV vs JSON: When to Use Each

Excel (.xlsx/.xls) is the standard for formatted business data with multiple sheets, formulas, charts, and conditional formatting. CSV is a lightweight, universally-compatible format for flat tabular data that any spreadsheet or database tool can import. JSON is the standard for web APIs, configuration files, and NoSQL databases. Converting between these formats bridges the gap between business data and software systems.

Frequently Asked Questions

Is my Excel file uploaded to any server?

No. Your file never leaves your browser. All processing is done client-side using JavaScript. You can verify this by opening your browser's DevTools Network tab — there will be zero upload requests when you load a file.

What file formats are supported?

This tool supports .xlsx (Excel 2007+), .xls (Excel 97-2003), and .csv (comma-separated values) file formats. If you have .xlsb (binary workbook) or .ods (OpenDocument) files, try converting them to .xlsx first using Excel or LibreOffice.

What is the maximum file size?

There is no fixed limit — the maximum file size depends on your browser's available memory (RAM). Most modern browsers can handle files up to 50-100MB without issues. For very large files above 100MB, consider splitting the workbook into smaller sheets first.

Does it support multi-sheet workbooks?

Yes. When you load a workbook with multiple sheets, sheet tabs appear above the table. Click any sheet tab to view its data. When converting, only the currently selected sheet is exported. Supported formats (.xlsx and .xls) can contain multiple sheets; CSV files always have one sheet.

How does the JSON format differ between options?

Array of objects produces [{"Name":"Alice","Age":30}, ...] — each row is an object with column headers as keys. Array of arrays produces [["Name","Age"],["Alice",30], ...] — headers and rows are arrays. Keyed by column produces {"Name":["Alice","Bob"],"Age":[30,25]} — each column becomes an array keyed by the header name.

Are formulas in cells evaluated?

SheetJS evaluates basic formulas and returns the computed value when available. However, complex formulas with external references, macros, or volatile functions may not evaluate fully. For best results, save your Excel file with values (Paste Special > Values) before loading it into this viewer.

Can I view CSV files that use different delimiters?

Yes. SheetJS automatically detects common delimiters (comma, semicolon, tab) when parsing CSV files. If the auto-detection fails, you can specify the delimiter during conversion to CSV output. The viewer always displays the parsed data correctly regardless of the source delimiter.