Fixing "Unexpected token" in JSON

This error means JSON.parse() hit a character it didn't expect at a specific position. The message always names the offending character and its position — that's your starting point, not a red herring.

Read the error message first

A message like Unexpected token } in JSON at position 42 tells you exactly where to look: count 42 characters into the string, or paste it into a formatter that reports line/column instead of a raw offset (Cryonel's JSON Validator does this).

The five most common causes

1. Trailing comma

{"a": 1, "b": 2,} — the comma after the last value is invalid in JSON, even though it's fine in a JavaScript object literal. This is the single most common cause of this error.

2. Single-quoted strings

{'a': 1} — JSON requires double quotes for both keys and string values. Single quotes aren't valid JSON syntax at all.

3. Unquoted keys

{a: 1} — again valid JavaScript, invalid JSON. Every key must be a double-quoted string.

4. Comments

Standard JSON has no comment syntax. // note or /* note */ anywhere in the document will break parsing.

5. A truncated response

If the error position is at (or very near) the end of the string, the JSON was likely cut off — check for a network timeout, a response size limit, or a copy-paste that missed the closing bracket.

Fix it automatically

The first four causes above can be fixed automatically — paste the broken JSON into JSON Repair and it strips comments, converts quotes, and removes trailing commas for you, then reports any error that's left (which usually means cause #5: something structural, not a syntax nit).