Expected double-quoted property name in JSON

The message

The wording depends on what parsed the JSON:

• Chrome, Edge, and current Node.js: Expected double-quoted property name in JSON at position 22
• Older Chrome and Node.js: Unexpected token } in JSON at position 22
• Firefox: JSON.parse: expected double-quoted property name
• Python: Expecting property name enclosed in double quotes

The JSON formatter uses your browser's own parser, so it shows the same wording your browser would, with a line and column where the browser gives one.

Cause 1: a trailing comma

{
  "a": 1,
  "b": 2,
}

The comma after 2 promises another key, and the closing brace arrives instead. The error points at line 4, column 1. Delete the last comma. In an array such as [1, 2, 3,], the message names the bracket instead: Unexpected token ']'.

Cause 2: things JSON does not have

Each of these is valid JavaScript but not JSON. All three report Expected property name or '}' in Chrome.

{'a': 1}
{a: 1}
{
  // note
  "a": 1
}

Use double quotes for keys and strings, and remove comments. If you need notes in a config file, keep it in YAML or TOML and convert it. See Why comments disappear.

The opposite mistake

A missing comma between two keys gives a different message: Expected ',' or '}' after property value, pointing at the start of the second key.

{
  "a": 1
  "b": 2
}

The edge case

Some files that end in .json are not strict JSON. tsconfig.json and VS Code's settings.json accept comments and trailing commas, because those programs use a more lenient parser. package.json does not. Pasting a tsconfig.json with comments into a strict tool fails even though TypeScript reads it.