SheetJS (xlsx)
The most widely-used JavaScript library for reading and writing Excel files (XLSX, XLS, ODS, CSV, and 30+ spreadsheet formats). Works in both Node.js and browsers without native dependencies. Parses spreadsheet data to JavaScript arrays/objects and serializes JS data to spreadsheet files. Used for Excel report generation, data import from Excel uploads, and spreadsheet format conversion. The xlsx npm package is the Community Edition; SheetJS Pro adds advanced features.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Excel files can contain macros — SheetJS parses data only and doesn't execute macros, preventing macro-based attacks. Zip bomb risk for extremely nested xlsx files.
⚡ Reliability
Best When
You need to read or write Excel (.xlsx, .xls) files in JavaScript across Node.js and browser environments with comprehensive format support.
Avoid When
You only need CSV handling (use csv-parse), or need advanced Excel features like pivot tables and complex formulas.
Use Cases
- • Parse Excel file uploads (.xlsx, .xls) from users to extract data for import into databases or APIs
- • Generate Excel reports from data queries — create workbooks with formatting and multiple sheets for download
- • Convert between spreadsheet formats (xlsx → csv, ods → xlsx) programmatically in Node.js pipelines
- • Read financial or scientific data from Excel files as part of agent data processing pipelines
- • Create formatted Excel exports with headers, column widths, and cell styling for business reports
Not For
- • CSV-only use cases — use csv-parse or PapaParse for pure CSV; SheetJS overhead is unnecessary
- • Advanced Excel features (pivot tables, macros, charts) — SheetJS reads but doesn't fully support all advanced Excel features
- • Very large Excel files (100K+ rows) — consider streaming alternatives; SheetJS loads entire workbook into memory
Interface
Authentication
No authentication — file processing library.
Pricing
The xlsx npm package (Community Edition) is Apache 2.0 and free for most use cases. Check SheetJS Pro license for commercial use requirements.
Agent Metadata
Known Gotchas
- ⚠ Cell values are typed differently: XLSX.utils.sheet_to_json() auto-casts dates, numbers, booleans — disable with raw: true if you need exact cell value strings
- ⚠ Date handling is notoriously complex — Excel stores dates as serial numbers; SheetJS converts them but timezone and date serial number system (1900/1904) can cause off-by-one date errors
- ⚠ Memory usage for large files: entire workbook loads into memory — for files >50MB, implement streaming with XLSX.stream or consider server-side processing
- ⚠ Formula cells return formula string, not computed value — SheetJS doesn't evaluate formulas; use e field for formula, v field for cached value (last computed), w for formatted string
- ⚠ File format detection: always specify bookType when writing (xlsx, xls, csv) — auto-detection may produce wrong format
- ⚠ npm package (xlsx) vs SheetJS Pro: the npm package doesn't include all features (no streaming, limited styling) — check if your use case requires Pro features before committing to the free version
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for SheetJS (xlsx).
Scores are editorial opinions as of 2026-03-06.