JSON parse errors: what each message means

Look up the error message you’re seeing to find out what causes it and how to fix it. The JavaScript messages below are the ones Chrome, Edge, and Node.js 20 and later show. Firefox, Safari, and Python word them differently, and the Python versions are listed too.

Most JSON errors come down to one of two problems. Either the text you tried to parse isn’t JSON at all, which usually means an API request went wrong, or it’s JSON with a syntax mistake in it. If the error points to the very first character (position 0, or line 1 column 1), start with the first group.

If your JSON parses but an API still rejects it, the problem is usually the data rather than the syntax: a missing field, a number sent as a string, or a value that isn’t allowed. The JSON Schema validator finds those when you have the API’s schema.

Each entry includes a broken example you can open in the JSON validator. It underlines the error, and Fix My JSON repairs it. Your own JSON works the same way: paste it in, and it stays in your browser.

Finding where the error is

Most error messages tell you where the parser gave up. Take this example, where the comma after "Maya" is the mistake:

{"name": "Maya",}
                ^

Where	Message
Chrome, Edge, Node.js	`Expected double-quoted property name in JSON at position 16 (line 1 column 17)`
Python	`Expecting property name enclosed in double quotes: line 1 column 17 (char 16)`
Firefox	`JSON.parse: expected double-quoted property name at line 1 column 17 of the JSON data`

All three point to the same character, the } marked above. Line and column numbers start at 1, so column 17 is the 17th character. Chrome’s “position” and Python’s “char” count from 0 instead, which is why they say 16.

Notice that the parser stops at the }, one character after the comma that caused the problem. It only knows something is wrong once it reaches a character that can’t come next, so look at the reported spot and just before it.

In a long document, print the text around that spot. In JavaScript:

try {
  JSON.parse(text);
} catch (error) {
  const position = Number(error.message.match(/position (\d+)/)?.[1]);
  if (!Number.isNaN(position)) {
    console.log(text.slice(Math.max(0, position - 30), position + 30));
  }
}

In Python, JSONDecodeError has the position built in:

import json

try:
    data = json.loads(text)
except json.JSONDecodeError as error:
    print(f"Line {error.lineno}, column {error.colno}")
    print(text[max(0, error.pos - 30):error.pos + 30])

Or paste the JSON into the JSON validator. It highlights the line with the first error and links to the guide for that kind of mistake.

The input isn’t JSON

When the text isn’t JSON, the error almost always points to the first character. The fix is in the request or code that produced the text, not in the text itself.

The text is an HTML page

JavaScript: Unexpected token '<', "<!DOCTYPE "... is not valid JSON; Unexpected token < in JSON at position 0
Python: Expecting value: line 1 column 1 (char 0)

The server sent a web page instead of JSON. It’s usually a 404 page, a login page, or an error page from a proxy.

Example

<!DOCTYPE html>
<html>
<head><title>404 Not Found</title></head>
</html>

Fix My JSON can’t turn a web page into JSON. The fix is in the request that returned it. Open it in the validator

Why APIs return HTML, and how to find out what happened

The text is empty or cut off

JavaScript: Unexpected end of JSON input; JSON Parse error: Unexpected EOF
Python: Expecting value: line 1 column 1 (char 0)

The response had no body, such as a 204 No Content response, or the JSON stops before its closing brackets.

Example

{
  "id": 42,
  "roles": ["editor", "admin"

Fix My JSON closes the open brackets, but it can’t bring back what was cut off. Open it in the validator

How to handle empty and truncated responses

The value isn’t JSON text

JavaScript: "undefined" is not valid JSON; "[object Object]" is not valid JSON

JSON.parse was given undefined, or an object that has already been parsed. response.json() and axios’s response.data both return parsed objects, so there’s nothing left to parse.

What each unexpected character means

An invisible character at the start

JavaScript: Unexpected token '', "{"a":1}" is not valid JSON
Python: Unexpected UTF-8 BOM (decode using utf-8-sig)

The file begins with an invisible byte order mark (BOM), which the JSON standard doesn’t allow. Save the file as UTF-8 without BOM, or in Python open it with encoding="utf-8-sig".

Example

{"id": 42}

Fix My JSON removes the invisible mark. Open it in the validator

Reading files that start with a BOM

The JSON has a syntax error

These errors point somewhere in the middle of the text. They’re most common in JSON that was written by hand or put together by joining strings, which is a good reason to generate JSON with JSON.stringify or json.dumps instead.

A property name isn’t in double quotes

JavaScript: Expected property name or '}' in JSON at position 1; Expected double-quoted property name in JSON at position 16
Python: Expecting property name enclosed in double quotes

A property name uses single quotes or no quotes, there’s a comma right before }, or there’s a comment. This usually means the text is a Python dictionary or a JavaScript object rather than JSON.

Example

{'name': 'Maya', age: 30}

Fix My JSON adds the missing double quotes. Open it in the validator

Fixing property names, quotes, and comments

A trailing comma

JavaScript: Expected double-quoted property name in JSON at position 16; Unexpected token ']', "[1,]" is not valid JSON
Python: Expecting property name enclosed in double quotes; Expecting value

There’s a comma after the last item in an object or array. JavaScript allows that in code, but JSON doesn’t.

Example

{"tags": ["api", "json",],}

Fix My JSON removes both extra commas. Open it in the validator

Removing trailing commas safely

A value is missing or invalid

JavaScript: Unexpected token 'N', "{"a": NaN}" is not valid JSON
Python: Expecting value: line 1 column 7 (char 6)

A value is missing, as in "a": ,, is in single quotes, or is something JSON doesn’t support, such as NaN, undefined, or Python’s None.

Example

{"id": 7, "owner": , "score": NaN}

Fix My JSON fills in the missing value with null. It turns NaN into the text “NaN”, so replace that with a real number or null. Open it in the validator

Finding and fixing the bad value

A missing comma or colon

JavaScript: Expected ',' or '}' after property value in JSON at position 8; Expected ',' or ']' after array element in JSON at position 3; Expected ':' after property name in JSON at position 5
Python: Expecting ',' delimiter; Expecting ':' delimiter

Two items aren’t separated by a comma, or a property name isn’t followed by a colon. An unescaped " inside a string causes the same error, because the parser thinks the string ends there. If the position in the message equals the length of your text, the JSON was cut off.

Example

{"id": 7 "name": "Maya"}

Fix My JSON adds the missing comma. Open it in the validator

Extra text after the JSON

JavaScript: Unexpected non-whitespace character after JSON at position 7
Python: Extra data: line 2 column 1 (char 8)

There’s more text after the JSON value ends, often a second JSON object. A file with one JSON value on each line is JSON Lines (also called NDJSON), and each line has to be parsed separately.

Example

{"id": 1}
{"id": 2}

Fix My JSON wraps the two objects in an array. If the file is JSON Lines, parse each line on its own instead. Open it in the validator

A line break or tab inside a string

JavaScript: Bad control character in string literal in JSON at position 10
Python: Invalid control character at: line 1 column 11 (char 10)

A string contains an actual line break or tab character. Inside JSON strings, these have to be written as \n and \t. JSON.stringify and json.dumps escape them automatically, and so does the JSON escape tool.

Example

{"note": "line one
line two"}

Fix My JSON escapes the line break as \n. Open it in the validator

A string is never closed

JavaScript: Unterminated string in JSON at position 12
Python: Unterminated string starting at: line 1 column 7 (char 6)

A string is missing its closing quote. Either the text was cut off, or a quote inside the string wasn’t escaped as \".

Example

{"name": "Maya}

Fix My JSON closes the string. Check the result, because it can’t know where the string was meant to end. Open it in the validator

Python can write invalid JSON

By default, Python’s json.dumps writes NaN and infinity as they are, so json.dumps({"x": float("nan")}) produces {"x": NaN}. Python can read that back, but JSON.parse and most other parsers reject it. Convert these values to None before encoding, or pass allow_nan=False so that json.dumps raises an error instead of writing invalid JSON. JavaScript’s JSON.stringify writes null for these values.