JSON Validator

JSON Validator is a free online tool that checks whether a JSON string is syntactically valid and provides clear error messages when it is not. Paste your JSON, click validate, and the tool either confirms the JSON is valid or identifies exactly what is wrong — the nature of the error and often the position where the problem occurs. Fix the error, re-validate, and repeat until your JSON is clean.

Invalid JSON is one of the most common sources of bugs in API integrations, configuration files, and data pipelines. JSON syntax is strict — stricter than most developers realise when coming from JavaScript, where trailing commas, single quotes, and unquoted keys are all acceptable. In JSON, every key must be a double-quoted string, every string value must use double quotes, no trailing commas are allowed after the last property or array element, and boolean and null values must be lowercase (true, false, null — not True, False, None, or NULL).

The most common JSON syntax errors are: missing or mismatched quotation marks around keys or string values; trailing commas after the last property in an object or last item in an array — valid in JavaScript but forbidden in JSON; single quotes used instead of double quotes; comments included in the JSON (JSON supports no comment syntax of any kind); numeric values with leading zeros (e.g., 007) which are invalid; and unescaped special characters in strings (backslashes, newlines, and tabs must be escaped as \\, \n, and \t).

JSON validation is a critical step before using JSON data in production. Unvalidated JSON passed to a parser throws exceptions that crash applications or cause silent data failures. Configuration files loaded at application startup that contain invalid JSON prevent the application from starting. API responses accepted without validation and deserialised directly into database records can corrupt stored data. Adding a validation step — using this tool during development or a validation library in production code — prevents these entire classes of errors.

Developers use JSON Validator when debugging API integrations where a response payload is causing a parse error. Content managers use it when manually editing JSON configuration files in CMS platforms and headless content systems. Data engineers validate JSON records in pipelines before loading them into databases. DevOps engineers validate Kubernetes manifests, Terraform variable files, and application configuration before deployment. QA testers validate API response formats against expected schemas during regression testing.

JSON Validator is distinct from JSON Schema validation. Syntax validation — what this tool does — checks whether the JSON is well-formed according to the JSON specification: correct syntax, valid data types, properly escaped strings. JSON Schema validation checks whether the JSON content matches a defined structure — required properties present, values within allowed ranges, arrays containing expected element types. Use this tool for syntax validation; use a dedicated JSON Schema validator library in your codebase for content validation.

JSON Validator processes your input in your browser using JavaScript's JSON.parse() function, which throws a SyntaxError with a descriptive message when the JSON is malformed. The error message is captured and displayed with additional context to help you locate and fix the problem. No data is sent to any server. The validator handles JSON of any size and complexity and works offline once the page has loaded.