What causes 'Unexpected token' errors in JSON?

The most common causes are: trailing commas after the last item in an object or array, unquoted keys (JavaScript object notation is not JSON), single quotes instead of double quotes, and smart curly quotes pasted from word processors like Microsoft Word or Google Docs.

Does JSON allow trailing commas?

No. Standard JSON (defined in RFC 8259 and ECMA-404) does not allow trailing commas. JavaScript objects do allow them, which is a common source of confusion. If your JSON has trailing commas, it is not valid JSON — it is JavaScript Object Notation or JSONC (JSON with Comments).

How do I fix smart quotes in JSON from Microsoft Word?

Smart quotes (“” ‘’) are typographic quotation marks used by word processors. JSON requires straight ASCII double quotes ("). Use a JSON repair tool to automatically replace smart quotes, or do a find-and-replace in a plain text editor before parsing.

JSON Repair

Developer Guide

Fix Broken JSON Instantly — Trailing Commas, Unquoted Keys, Smart Quotes

JSON parse errors are frustrating because the error messages rarely tell you what actually went wrong. This guide covers every common way JSON breaks, shows you the exact before/after, and gives you a one-click repair tool for when you just need it fixed now.

April 29, 2026

9 min read

PDF Mavericks Team

Skip to the fix: Paste your broken JSON into our JSON formatter and click the Repair tab. It uses the jsonrepair library (1,500+ GitHub stars) to auto-fix the most common issues.

Table of Contents

Trailing Commas
Unquoted Keys
Single Quotes
Smart Quotes from Word / Google Docs
Comments in JSON
Missing Commas Between Properties
Truncated / Incomplete JSON
How to Read JSON Error Messages

Trailing Commas

This is the number one source of broken JSON. JavaScript objects allow trailing commas since ES5, which means any JSON exported from a JS file or config system may carry them. Standard JSON (RFC 8259) rejects trailing commas entirely.

Trailing comma in an object

BROKEN

{ "name": "Jane", "role": "admin", }

FIXED

{ "name": "Jane", "role": "admin" }

Remove the comma after the last property. JSON objects and arrays cannot have a comma after the final item.

Trailing comma in an array

BROKEN

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

FIXED

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

The comma after "rest" is invalid. Array elements follow the same rule — no trailing comma.

If you write TypeScript/JavaScript and need trailing commas in your source code (common in Prettier config), use JSONC format or convert to plain JSON before sharing.

Unquoted Keys

JavaScript objects allow unquoted keys. JSON does not. If you've copied an object literal from a JavaScript file, the keys won't have quotes.

Unquoted keys (JavaScript object literal)

BROKEN

{ name: "Jane", age: 30, active: true }

FIXED

{ "name": "Jane", "age": 30, "active": true }

Every key in JSON must be wrapped in double quotes. This is one of the most meaningful differences between JSON and JavaScript object notation.

The fix is mechanical: wrap each key in quotes. A repair tool handles this automatically. If you're doing it manually, be careful with keys that contain hyphens or spaces — they still need quotes in JSON.

Single Quotes

Python developers frequently hit this one. Python's str(dict) and repr() output uses single quotes. JSON only accepts double quotes.

Single-quoted strings (Python repr output)

BROKEN

{'name': 'Jane', 'active': True, 'count': 5}

FIXED

{"name": "Jane", "active": true, "count": 5}

Two problems here: single quotes need to become double quotes, and Python boolean True becomes JSON true (lowercase). Use json.dumps() in Python instead of str() to get valid JSON.

Python tip: Never use str(my_dict) to produce JSON. Always use import json; json.dumps(my_dict). The output is valid JSON every time.

Smart Quotes from Word / Google Docs

Word processors auto-convert straight quotes (") to typographic "smart quotes" (“ and ”). When you copy JSON from a document that was edited in Word or Google Docs, these curly characters break every parser.

Smart quotes from a word processor

BROKEN

{“name”: “Jane Doe”, “role”: “admin”}

FIXED

{"name": "Jane Doe", "role": "admin"}

The curly open-quote (“) and close-quote (”) characters are not valid JSON string delimiters. Replace them with standard straight double-quote characters (ASCII 0x22).

This is particularly painful because smart quotes look almost identical to regular quotes in most fonts. The error message (Unexpected token ‘ at position 0) is the tell.

Comments in JSON

JSON has no comment syntax. None. Not //, not /* */, not #. If you've copied a JSONC (JSON with Comments) config file — common in VS Code settings, TypeScript configs, and ESLint configs — you need to strip the comments before parsing.

JSONC with comments (VS Code-style)

BROKEN

{ // Database settings "host": "localhost", "port": 5432, /* default port */ "name": "mydb" }

FIXED

{ "host": "localhost", "port": 5432, "name": "mydb" }

Remove all comment lines and inline comments. If you need comments in your config, keep it as .jsonc and use a JSONC parser (like strip-json-comments) before passing to JSON.parse().

Missing Commas Between Properties

Less common but happens when JSON is generated by string concatenation or edited manually:

Missing comma between properties

BROKEN

{ "name": "Jane" "role": "admin" }

FIXED

{ "name": "Jane", "role": "admin" }

Every property in a JSON object must be separated by a comma, except for the last one. A missing comma triggers a SyntaxError pointing to the line after the gap.

Truncated / Incomplete JSON

APIs that hit size limits, log truncation, or clipboard paste errors can leave you with JSON that simply ends mid-way. The jsonrepair library (used in our Repair tab) can often close open strings, arrays, and objects intelligently.

Truncated JSON (missing closing brackets)

BROKEN

{"users": [{"name": "Jane", "id": 1}, {"name": "Bob"

FIXED

{"users": [{"name": "Jane", "id": 1}, {"name": "Bob"}]}

Repair tools close open structures at the end. The repaired output is best-effort — always verify that the inferred structure matches your intent before using the result.

How to Read JSON Error Messages

JavaScript's JSON.parse() throws SyntaxError with position information. Here's a quick decoder:

Unexpected token } at position 47

Cause: Trailing comma before the closing bracket

Fix: Remove the comma at position ~45

Unexpected token ‘ at position 0

Cause: Smart quote (curly quote) instead of double quote

Fix: Replace all smart quotes with straight quotes

Unexpected token a at position 12

Cause: Unquoted key — parser hits the letter and stops

Fix: Wrap keys in double quotes

Unexpected end of JSON input

Cause: Truncated JSON — file cut off before closing

Fix: Close open arrays and objects

Unexpected token / at position 5

Cause: Comment in JSON (// or /* */)

Fix: Remove all comments

Repair JSON in One Click

Paste your broken JSON, hit the Repair tab. Our formatter uses the jsonrepair library to fix trailing commas, unquoted keys, single quotes, smart quotes, missing brackets, and more — browser-side, no data sent anywhere.

Open JSON Repair Tool