What is JSON?
JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format. It was popularised by Douglas Crockford in the early 2000s and is now the dominant format for API responses, configuration files, and data storage on the web. JSON is defined in RFC 8259 and ECMA-404.
A JSON document looks like this:
{
"name": "Alice",
"age": 30,
"active": true
}
JSON supports six value types: string, number, boolean, null, object (key-value pairs), and array. Its syntax is a strict subset of JavaScript object literal syntax, which is why "JavaScript" is in the name — though JSON is language-independent and is used with Python, Go, Rust, Java, C++, and virtually every other language.
What is JASON?
JASON (all caps) is an unrelated acronym and name that comes up in a few different contexts:
- A given name — JASON is an alternative capitalisation of the name Jason, sometimes used as an acronym-style moniker. When people search for "JASON format" or "JASON data," they almost always mean JSON.
- JASON Advisory Group — a secretive US Department of Defense scientific advisory panel that has advised on military and national-security topics since the 1960s. No relation to data formats.
- JASON (NASA instrument) — a series of satellite altimetry missions (Jason-1, Jason-2, Jason-3) operated by NASA and CNES to measure sea-surface height. Also unrelated to data formats.
How is JSON pronounced?
Douglas Crockford, who named and popularised the format, pronounces JSON exactly like the name "Jason" — /ˈdʒeɪsən/. He chose the name partly as a quiet joke: he is himself named Douglas, and he named the format after a colleague.
In practice you'll also hear "JAY-sawn" (rhymes with "drawn") in many developer communities, especially in the UK and among people who default to pronouncing all letters. Both are widely understood. The RFC and ECMA specs are silent on pronunciation.
The "J" is definitely not silent, and it's not an acronym you spell out letter by letter ("jay-ee-es-oh-en") — though you occasionally hear that too.
Summary
| Term | What it is |
|---|---|
| JSON | JavaScript Object Notation — a data interchange format |
| JASON (name) | A person's name; alternate spelling of Jason |
| JASON (advisory group) | US DoD scientific advisory panel — no relation to JSON |
| Jason (NASA) | Satellite altimetry missions — no relation to JSON |
If you arrived here looking for JSON tools, you're in the right place — see the JSON Formatter, JSON Validator, or What is JSON? for a full introduction to the format.