What is JSON?

JSON is a text format for nested data: objects with named keys, arrays, strings, numbers, booleans and null. It has no date type and no comments.

Who uses it

Every web API, most configuration files and anything that talks to JavaScript.

Reading JSON

Four shapes all read correctly: an array of objects, an array of arrays with a header row, an object of column arrays, and an object keyed by row id. A single wrapper key holding the array, which is how most APIs reply, is unwrapped automatically. Nested objects are flattened one level into dotted keys; anything deeper is kept as JSON text in the cell, because a table cannot hold a tree.

Writing JSON

You choose the shape. An array of objects is the default and the one most code expects. A 2D array is smaller. Column arrays suit charting libraries. A keyed object suits lookups by id.

The specification

JSON is defined by ECMA-404. Reading the primary source settles most arguments about edge cases faster than searching for them does.

What it can hold

JSON is a data interchange format. JSON writes a table as an array of objects, repeating the column names on every row, which is why it is larger than the table it came from. A machine can read the table back out of it without guessing, which is what makes it safe to convert into and out of.

It keeps

Types. A number stays a number and a boolean stays a boolean, so whatever reads the file next does not have to guess from how a value looks.
The difference between empty and missing, which most table formats cannot express at all.
Nested values. A cell can hold a list or an object rather than only a single value.
A line break inside a cell, which survives rather than ending the row.

It cannot express

Any formatting. Bold, colour, column widths and merged cells have nowhere to go.
A partial read. The document has to be complete to mean anything, so a truncated file yields nothing and a large one has to be held in memory whole.
A header row. Column names are repeated on every record instead, which is why a file in this format is larger than the table it holds.

What it looks like

Example JSON

[
  { "id": "007", "name": "Halima Yusuf", "role": "Analyst, data", "started": "2024-03-15", "hours": "38.5" },
  { "id": "012", "name": "Jonah \"Jo\" Pryce", "role": "Engineer", "started": "2025-11-02", "hours": "" },
  { "id": "104", "name": "Wei Chen", "role": "Manager", "started": "2023-06-30", "hours": "40" }
]

Questions

Why did my zip code lose its leading zero?

Type inference turned the text 07030 into the number 7030. Tablizer leaves inference off by default for exactly this reason, and refuses to convert any value starting with a zero followed by a digit even when it is on.

How do I open JSON files?

Any text editor will show you the contents. To read it as a table, paste it into the converter on this site and it appears in an editable grid. Nothing is uploaded.

Is JSON a good format for sharing data?

It depends who is receiving it. Every web API, most configuration files and anything that talks to JavaScript. If the recipient is outside that group, a plain CSV travels further than anything else.