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Learn JSON

JSON has objects, arrays, strings, numbers, booleans and null. Strings and object keys use double quotes.

Read each short explanation, work through the example, then answer a pop quiz. Every answer explains the reasoning. Incorrect answers unlock a fresh question on the same idea; the full lesson contains ten questions.

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01Understand the basics

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JavaScript Object Notation (JSON) is a text format for exchanging data. Objects use named properties; arrays hold ordered items. Strings and property names use double quotes. JSON supports numbers, booleans and null, but not comments or trailing commas.

Section 1 question · 4 variations

Which is valid JSON?

{'active': true}{"active":true}{"active":True}

02Keep types meaningful

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The number 42 and the string "42" are different values. Arrays preserve order; an object maps property names to values. Use the types expected by the receiving system.

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Array item count: 3Move the slider or use the arrow keys to see what changes.

{"items":[{"id":1,"active":true},{"id":2,"active":true},{"id":3,"active":true}]}Parse syntaxValidate schema

Section 2 question · 3 variations

Which value is a boolean?

"false"false"0"

03Validate the contract

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Parsing checks syntax. A schema can check required fields and value types. Business checks decide whether the values make sense for the real operation.

Section 3 question · 3 variations

Does valid JSON guarantee acceptable business data?

YesNoOnly when formatted

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Learn JSON

01Understand the basics

02Keep types meaningful

Try a different value

03Validate the contract

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