How to Validate JSON and Find Syntax Errors

What is JSON Validation?

JSON Validation is the process of checking if a JSON text strictly complies with standard JSON syntax specification guidelines (RFC 8259). A single out-of-place comma or mismatched bracket will cause standard parsers to crash, breaking downstream frontend interfaces or backend applications.

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Step-by-Step Validation Guide

If your application is failing with “Unexpected token…” or similar exceptions, follow this routine:

Step 1: Feed It to an Online Validator

The fastest diagnostic tool is our browser-based JSON Validator Online. Paste your JSON, and click Validate. If it is broken, the engine will extract the character index and line number where the problem lies.

Step 2: Look for Typical Culprits

Standard validation failures are almost always caused by one of these three mistakes:

1. Trailing Commas: A comma placed after the final array item or object property.
2. Invalid Quotes: Single quotes (') instead of standard double quotes (").
3. Mismatched Brackets: Opening a brace { but closing with an array bracket ].

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Programmatic Validation Examples

Validation in JavaScript / Node.js

In Node.js or browser JS, you can validate JSON inside a try/catch block:

function isValidJSON(jsonString) {
  try {
    JSON.parse(jsonString);
    return true;
  } catch (e) {
    console.error("Syntax Error at position:", e.message);
    return false;
  }
}

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Frequently Asked Questions

Can a JSON string have trailing commas?

No. Standard JSON strictly forbids trailing commas. The parser expects another key/value pair if it encounters a comma.

What is the difference between validation and linting?

Validation checks if the file adheres to syntactical rules (i.e. is parseable). Linting may check style preferences like indentation and key-sorting guidelines.