XLSX to JSON for seed data, configs and API payloads

Developers often get data as XLSX from colleagues: seed data for a database, feature flags, country lists, test fixtures. Writing a one off script for each file wastes time, and the result has to be maintained every time the sheet changes.

XlsConverter turns the workbook into JSON that is ready to commit or post, with stable key names and correct types. Excel to JSON covers nested objects in depth, XLS to JSON covers the legacy format, and CSV to JSON handles plain text input.

How to convert XLSX to JSON in three steps

1. 1Upload the .xlsx workbook.
2. 2Pick the sheet, key style and JSON array or JSON Lines output.
3. 3Convert and download, or fetch the result through the API.

Precision loss when large Excel numbers reach JavaScript

JavaScript and many JSON parsers store numbers as 64 bit floating point, the same as Excel, so integers above 9,007,199,254,740,991 lose precision. Excel itself keeps only 15 significant digits, which means a 16 or 18 digit order number typed as a number is already damaged in the workbook. When such IDs are stored as text in the sheet we keep them as JSON strings, and the number handling option forces any ID column to strings.

JSON Lines suits large sheets and streaming pipelines: each row is a complete JSON object on its own line, so a consumer can process the file without loading it all, and appending is trivial. A single array suits config files and small seed sets that are read in one go. Both use UTF-8 without a BOM, which is what JSON parsers expect.

Stable keys matter when the JSON lives in a repository. A colleague renaming a column from Country Code to Country ISO would silently change every key. A saved mapping template pins the output key names, so the JSON stays the same shape even when the sheet headers drift. For loading the same data into a database directly, see XLSX to SQL or Excel to SQLite.