JSON Validation: How to Find and Fix Broken JSON Fast

You've been here. You paste JSON into a tool, an API, or a config file — and get back something like Unexpected token at position 47. Or worse: Invalid JSON with no further information.

JSON validation errors are fixable once you understand what the parser is actually complaining about. Here's how to read them and fix them fast.

Why JSON Parsing Fails

JSON has strict rules. The parser is not being pedantic — it's following the spec. Common failure points:

1. Trailing Commas

{
  "name": "Toolblip",
  "version": "1.0",   ← trailing comma = error
}

JSON parsers expect no comma after the last item in an object or array. Remove the comma.

2. Single Quotes

{
  'name': 'Toolblip'   ← single quotes are not valid JSON
}

JSON requires double quotes for both keys and string values. Always use " not '.

3. Comments

{
  // This is not valid JSON
  "name": "Toolblip"
}

JSON has no concept of comments. If you need comments, move them outside the JSON structure or use a different format.

4. Unquoted Keys

{
  name: "Toolblip"   ← unquoted key = error
}

JSON requires all keys to be double-quoted strings. "name" is valid; name is not.

5. Trailing Characters After the Closing Bracket

If you get an error at the very end of your JSON, you probably have extra text after the closing } or ]. Check for a stray character, a BOM (byte order mark), or text that got appended accidentally.

6. Newlines in Strings

{
  "bio": "Line one
  Line two"   ← raw newline in string = error
}

Strings in JSON cannot contain raw newlines. Use \n instead:

{
  "bio": "Line one\nLine two"
}

How to Read the Error Position

Many JSON validators report position X in the error message. This is the character offset from the start of the string. Here's how to use it:

1. Copy your JSON into a text editor with a character count display
2. Go to character position X
3. Look at the character at that position and the few characters before it

Most errors are at or very near the actual problem — the parser often can't detect the error until it tries to parse what comes next.

Validating JSON Programmatically

JavaScript

try {
  const parsed = JSON.parse(jsonString);
  console.log('Valid JSON', parsed);
} catch (e) {
  console.error('Invalid JSON:', e.message);
}

Python

import json

try:
    parsed = json.loads(json_string)
    print("Valid JSON", parsed)
except json.JSONDecodeError as e:
    print(f"Invalid JSON at position {e.pos}: {e.msg}")

PHP

$result = json_decode($json_string);
if (json_last_error() !== JSON_ERROR_NONE) {
    echo "Invalid JSON: " . json_last_error_msg();
}

Pro Tips

1. Format Before Debugging

Minified JSON is nearly impossible to read. Always format it first — one misplaced comma is easy to miss in a wall of text.

Format your JSON →

2. Validate in Your Editor

Most code editors have JSON validation built in:

• VS Code — errors shown in the Problems panel, red underlines
• Sublime Text — JSON syntax checking via sublime-json
• IntelliJ/WebStorm — real-time validation with line-level error markers

3. Use jq for Command-Line JSON

jq is a command-line JSON processor. Great for validating, querying, and transforming JSON in scripts:

# Validate JSON
echo '{"name":"Toolblip"}' | jq empty   # succeeds, no output
echo '{"name"}' | jq empty              # error: parse error

# Pretty print
cat data.json | jq .

4. Check for BOM Issues

If your JSON validates in a browser tool but fails in code, you might have a UTF-8 BOM (byte order mark). This invisible character EF BB BF at the start of a file confuses many JSON parsers. Save your file as "UTF-8 without BOM" in your editor.

JSON vs JSONC

If you're working in VS Code, your settings.json or tsconfig.json might be JSONC — JSON with Comments. VS Code uses JSONC to allow // and /* */ comments in config files. These are not valid JSON and will fail if parsed with a standard JSON parser.

TL;DR Error Guide

Error	Cause
Unexpected token	Bad character, usually a quote or comma issue
Unexpected end of JSON	Missing closing bracket or brace
Unexpected number	Missing quotes around a string value
Unexpected string	Unquoted key or wrong quote type
Missing : after property	Key without its colon separator
Missing , after property	Missing comma between fields
Position X	Count X characters from start to find the problem

Validate and format your JSON →

Paste any JSON — formatted, minified, or broken — and get back a clean error message with the exact line and character position of the problem.