JSON to Excel Converter with Nested Object Flattening

What the JSON to Excel converter produces

Paste JSON or drop a .json file and the tool builds a real .xlsx workbook — not a CSV renamed to .xlsx — with a bold, frozen header row and columns sized to their content. Numbers stay numeric and booleans stay TRUE/FALSE, so you can sort, filter and sum straight away, while strings are written exactly as they are, leading zeros included.

Everything happens in your browser. The JSON is parsed with JSON.parse, flattened in JavaScript and packed into the XLSX format locally, which matters when the data is an API response full of customer records, tokens or internal IDs that should not be pasted into a third-party server.

How each JSON shape is mapped to sheets

An array of objects is the common case — the output of most REST endpoints and database exports. Each object becomes a row, and the columns are the union of every key that appears in any object, in the order they are first seen, so a field present only in record 500 still gets a column; rows that lack it get an empty cell.

Nested objects are flattened into dot-path columns: {"address": {"city": "London", "geo": {"lat": 51.5}}} becomes address.city and address.geo.lat. Arrays are the awkward part, because a list does not fit in one cell. By default they are kept as compact JSON text such as ["admin","beta"], which is lossless and easy to parse back. Switch to "Expand to columns" and each element gets its own indexed column — tags.0, tags.1, and items.0.price for arrays of objects — which suits short, fixed-length lists better.

Other shapes work too. An array of arrays is written as rows exactly as given, the natural format for tabular data that already has a header row inside it. An array of plain values becomes a single "value" column. A single object becomes one row. An object whose values are all arrays — {"users": [...], "orders": [...]} — becomes a workbook with one sheet per key, named after the key, which is the quickest way to turn a multi-collection export into a tabbed spreadsheet.

Limits worth knowing

Excel caps a cell at 32,767 characters and a sheet at 1,048,576 rows and 16,384 columns; longer text is truncated to fit. Sheet names are limited to 31 characters and may not contain [ ] : * ? / or \, so keys like "2024/Q1" are cleaned to "2024_Q1" and duplicates receive a numbered suffix. JSON numbers outside the range of a double, or integers above 2^53, are already rounded by JSON.parse before the conversion starts; keep such IDs as strings in the source JSON. Very deep or very wide objects work but produce correspondingly wide sheets, so trimming the payload first with jq or a quick script often gives a more readable result. If the JSON fails to parse, the error message from the parser is shown so you can fix it — or run it through the JSON formatter first. Going the other way, the Excel to JSON tool turns a sheet back into an array of objects.