Missing Comma in JSON: How to Spot It

Quick answer: JSON uses a comma to separate items inside an object or array — one between each pair, none after the last. A missing comma produces errors like Expected ',' or '}' after property value in JSON or Unexpected string in JSON. The fix is to add the comma between the two members. To land on the exact spot, paste the document into the JSON Debugger.

A comma goes between members, never before the first or after the last:

{
  "a": 1,
  "b": 2,
  "c": 3
}

Two commas, for three members. The mirror image of this rule is the trailing comma error — a comma where there shouldn't be one. A missing comma is the opposite: a boundary with no separator.

{
  "name": "Dana"
  "role": "admin"
}

After "Dana" the parser expects either a comma (another property follows) or } (the object ends). Instead it finds "role", so it reports something like Expected ',' or '}' after property value — with the position pointing at the start of "role". The same happens in arrays:

[1 2 3]

Expected ',' or ']' after the 1. The fix is [1, 2, 3].

Missing commas usually come from hand-editing:

• You added a new property but forgot the comma on the line above it.
• You reordered lines and the comma ended up in the wrong place.
• You pasted two objects together without a separator.

Because the error points at the next token (the thing that appeared where a comma should be), people look at "role" and see nothing wrong with it — the real fix is on the line before. Always look at the boundary between the highlighted token and the one above it.

1. Read the position from the error and jump to it with the JSON Debugger.
2. Look at the end of the previous line — that's where the comma belongs.
3. Add the comma, then re-check with the JSON Validator.

The durable fix is to stop writing JSON by hand. JSON.stringify() always inserts commas correctly, so generating JSON from data eliminates the whole class of comma errors — see Parse and Stringify.

Where do commas go in JSON? Between members of an object or array — one comma for each gap. There's no comma before the first member or after the last.

What error does a missing comma cause? Usually Expected ',' or '}' (objects) or Expected ',' or ']' (arrays), or an "unexpected" token error pointing at the member that came right after the missing separator.

The error points at a line that looks correct — why? The reported token is the one that appeared where a comma was expected. The missing comma is on the line before it, so check the previous member's end.

How do I avoid missing commas entirely? Generate JSON with JSON.stringify() (or json.dumps() in Python) instead of typing it. Serializers always place commas correctly.