Xlsx

This is your reference for working with Excel files programmatically, covering both Python libraries (openpyxl for formatting and cell manipulation, pandas for data operations) and JavaScript's xlsx package. You'll reach for this when reading spreadsheets, writing structured data, applying formulas, or converting between Excel and CSV formats. The examples are concise and cover the common patterns you actually need: iterating rows, styling cells, pivoting data, and merging multiple files. It's designed as a quick lookup rather than a tutorial, so you can grab the syntax and get back to work. The pandas examples are especially useful if you're doing any data transformation before writing output.