Validate JSON online for free. Check JSON syntax, find errors, identify the line and column where a problem occurs, and understand what needs to be fixed before using your JSON in an API, application, configuration file, or development project.
A JSON Validator is an online tool that checks whether a piece of text follows the syntax rules required for valid JSON. JSON is widely used for APIs, web applications, configuration files, data exchange, automation workflows, and communication between software systems. When a small syntax mistake is introduced, an application may reject the entire document. A validator helps identify that problem before the JSON is used elsewhere.
ToolifyClub's JSON Validator Online lets you paste JSON directly into the browser and check it without installing a separate application. When the input is valid, the tool confirms the result and provides basic information about the JSON. When the input is invalid, it attempts to identify the error position and explains common causes such as missing commas, incorrect quotes, invalid values, or mismatched brackets.
JSON itself is a lightweight, text-based format for representing structured data. The JSON standard defines objects, arrays, strings, numbers, booleans, and null as the core data types.
JSON errors are often caused by very small characters. A missing comma, an extra comma, an incorrectly quoted property, or a closing bracket in the wrong place can make otherwise useful data invalid. These mistakes can be difficult to find when the JSON contains hundreds or thousands of lines.
A JSON validator provides a quick syntax check before you send data to an API, save a configuration file, commit code, or pass data to another application. Instead of waiting for an application to reject the document, you can test the JSON first.
The main advantage of a browser-based JSON validation tool is speed. You can paste the data, validate it, inspect the error information, make the correction, and validate it again without installing a dedicated JSON editor.
ToolifyClub's JSON Validator is designed for everyday development, debugging, API testing, configuration work, and quick syntax checks.
JSON follows a defined syntax rather than accepting every value that
JavaScript happens to support. A JSON value can be an object, array,
number, string, true, false, or
null. Objects contain name/value pairs and arrays contain
ordered values.
JSON object property names are strings, which means they are written using double quotes. Values are separated using commas, while a colon separates an object property name from its value. Curly braces define objects and square brackets define arrays.
Standard JSON also does not permit JavaScript-specific values such as
undefined, NaN, or Infinity.
Numbers follow JSON's number grammar and leading zeros are not allowed
in ordinary numeric representations.
Object properties and array elements normally need commas between them. Forgetting one is one of the most common JSON syntax mistakes.
{
"name": "Alex"
"age": 28
}Correct version:
{
"name": "Alex",
"age": 28
}A comma should not be placed after the final property or array item.
{
"name": "Alex",
"age": 28,
}Remove the final comma:
{
"name": "Alex",
"age": 28
}JSON strings and object property names use double quotation marks. JavaScript code may use single quotes in many situations, but that does not make single-quoted strings valid JSON.
{'name': 'Alex'}Correct:
{"name": "Alex"}{
name: "Alex"
}Correct:
{
"name": "Alex"
}
Values such as undefined, NaN, and
Infinity are not standard JSON values. If a system needs
to represent an unavailable value, null may be appropriate
depending on the application's data model.
{
"score": NaN
}A standard JSON-compatible alternative could be:
{
"score": null
}Every opening object or array delimiter needs the corresponding closing delimiter.
{
"users": [
{
"name": "Alex"
}
}The array needs to be closed before the object:
{
"users": [
{
"name": "Alex"
}
]
}Special characters inside JSON strings may need escaping. For example, a quotation mark inside a string must be represented using an escaped quotation mark rather than ending the string early.
{
"message": "He said "hello""
}Correct:
{
"message": "He said \"hello\""
}When a JSON parser reports an error position, it is telling you where it detected something unexpected. That location is not always the exact character where the original mistake was made.
For example, if a comma is missing between two properties, the parser may only realize there is a problem when it encounters the next property. This is why the reported position should be treated as the place to investigate, rather than an absolute guarantee that the previous character is the original mistake.
For large JSON documents, line and column information makes this investigation much easier. If your JSON is minified into one line, the line may simply be line 1 while the column or character position provides the more useful location.
{
"name": "Alex",
"age": 28,
"active": true,
"country": "Pakistan"
}[
"HTML",
"CSS",
"JavaScript",
"PHP"
]{
"user": {
"name": "Alex",
"profile": {
"verified": true,
"roles": [
"developer",
"admin"
]
}
}
}{
"name": "Alex",
"age": 28,
}
The final comma after 28 makes this invalid under standard
JSON syntax.
A JSON Validator and a JSON Formatter solve related but different problems. Validation asks whether the input follows JSON syntax. Formatting focuses on making valid JSON easier for humans to read.
| Task | JSON Validator | JSON Formatter |
|---|---|---|
| Check syntax | Yes | Usually |
| Find syntax errors | Primary purpose | Secondary function |
| Line / column diagnostics | Yes | Not always the focus |
| Beautify JSON | For valid input | Primary purpose |
| Minify JSON | Not the main purpose | Common feature |
If you are unsure whether your JSON is broken, start with a validator. Once it is valid, a formatter can make the structure easier to inspect.
JSON validation is useful in many development and technical workflows.
APIs frequently use JSON to exchange structured information between clients and servers. A malformed payload can cause a request to fail before the application reaches the business logic. Validating the payload first can therefore save time during API development and debugging.
If an API response looks strange, you can also paste the response into the validator to determine whether it is valid JSON. This is especially useful when a server unexpectedly returns HTML, plain text, or an incomplete response instead of the expected JSON document.
Experienced developers can use a JSON validator as a quick debugging utility, while beginners can use it to learn the structure of JSON. Seeing a validation error after changing one character can make JSON's syntax rules easier to understand.
The most important concept is that JSON is structured data with a defined grammar. Formatting can improve readability, but formatting cannot make invalid syntax valid. Validation should therefore come before relying on a JSON document in a system that expects standard JSON.
The core validation performed by this browser-based tool does not require an external JSON validation API. The JSON is processed by the JavaScript running in your browser for the validation features provided here.
Even when a tool processes data locally, you should still avoid pasting passwords, API keys, access tokens, private customer information, or other sensitive information into any online utility unless you have verified that the environment is appropriate for that data.
JSON validation is the process of checking whether a JSON document follows the syntax rules required for valid JSON. It can identify problems such as missing commas, incorrect quotation marks, invalid values, and mismatched brackets.
Paste your JSON into the ToolifyClub JSON Validator and click Validate JSON. The tool checks the input and reports whether it is valid. If an error is detected, it provides diagnostic information to help you investigate the problem.
Common JSON errors include missing commas, trailing commas, single quotes, unquoted property names, mismatched brackets, invalid escape sequences, and unsupported JavaScript values such as undefined, NaN, and Infinity.
Yes. Click Upload JSON and select a .json file from your device. Its contents will be loaded into the validator so you can check the syntax.
Yes. After the JSON has been successfully validated, you can use Format Valid JSON to create a readable, indented version.
No. undefined is a JavaScript value, not a standard JSON value. Standard JSON supports strings, numbers, objects, arrays, true, false, and null.
No. NaN is not part of standard JSON number syntax. If your data model needs a representation for a missing numeric value, null may be used where appropriate.
JSON strings use double quotation marks. Object property names are also strings, so standard JSON objects use double-quoted property names.
If your JSON is minified and contains no line breaks, the entire document is technically on line 1. In that situation, the column or character position can be more useful for locating the issue.
After validating your JSON, you may also need to format, inspect, or transform it. ToolifyClub's developer tools collection is designed for these everyday tasks.
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