JSON Validator

About this tool

Paste JSON and the validator tells you straight away whether it is valid. If it isn't, you get the line and column of the first error, the lines around it with a marker under the problem, and a plain-English hint: a trailing comma, single quotes, a missing value, a comment, or True instead of true. Valid JSON shows its type, number of keys, depth and size, so you can confirm you pasted all of it.

What a JSON validator checks

A validator checks syntax: that the text follows the JSON rules, so any program can parse it. It doesn't check what the data means. Checking that a price is a number above zero, or that an email field is present, is a job for JSON Schema.

The mistakes that break JSON most often

Most invalid JSON comes from a few mistakes: a comma after the last item, single quotes instead of double quotes, keys without quotes as in JavaScript code, comments, a missing comma between items, a line break inside a string, and NaN, undefined or True, which are not JSON. The validator gives you the fix for each; most are one character.

// invalid
{ name: 'Sara', "tags": ["a", "b",], }

// valid
{ "name": "Sara", "tags": ["a", "b"] }

Validate JSON in Python and C#

In code, parse the JSON and catch the error; both languages tell you the line and column.

# Python
import json

try:
    with open("data.json", encoding="utf-8") as f:
        json.load(f)
    print("valid")
except json.JSONDecodeError as e:
    print(f"line {e.lineno}, column {e.colno}: {e.msg}")

// C# with Newtonsoft.Json
try { JToken.Parse(text); Console.WriteLine("valid"); }
catch (JsonReaderException e) { Console.WriteLine($"line {e.LineNumber}, position {e.LinePosition}: {e.Message}"); }

Validating with a schema

To check the structure as well as the syntax, write a JSON Schema and validate against it: ajv in JavaScript, the jsonschema package in Python, or Newtonsoft.Json.Schema in .NET. Run this validator first: a schema check can't start until the JSON parses.