JSON Validator
Check whether a JSON text follows standard JSON syntax and understand why an input is accepted or rejected.
Check JSON syntax before using data
A missing quote, comma, or closing bracket can stop an API, configuration loader, or build step before it reaches the code that needs the data. JSON Validator gives you a focused place to check a source text against the JSON grammar and separate a syntax problem from later application checks.
Validation here means parsing the supplied text as JSON. A successful parse says that the structure is accepted by the validator. It does not say that required fields exist, values meet business rules, or the document matches a JSON Schema unless those checks are explicitly provided elsewhere.
Syntax validity and meaning are different
Standard JSON contains objects, arrays, strings, numbers, true, false, and null. Object names and strings use double quotes, members are separated by commas, and brackets must close in the correct order. Comments and trailing commas are not part of the standard grammar.
A validator answers a narrow question: can this source be parsed as JSON? It does not repair the source, execute embedded code, contact an API, or decide whether a value is useful to your application. Keep schema validation and domain checks as separate steps.
How to validate JSON
- Paste one complete JSON value into the source field.
- Run the validator and read the status or diagnostic result.
- For a rejected input, inspect quotes, commas, brackets, escapes, and the value near the reported area.
- After syntax passes, run any schema or application checks required by your project.
Validation method
- Read the grammar
The validator attempts to parse the complete source as a JSON value. The source must use the accepted tokens and nesting rules.
- Report acceptance or failure
A successful result indicates that parsing completed. A failure indicates that the source did not satisfy the syntax understood by the validator.
- Keep later checks separate
Schema constraints, required properties, ranges, and permissions are semantic checks. They need their own evidence and should not be inferred from a parse result.
Do not invent an exact line number or error message unless the tool actually returns it for the input.
Reading the validation result
A valid result means the submitted text was accepted as JSON syntax. You can then inspect its values or pass it to a schema and application-level check.
An invalid result means parsing stopped. Read the diagnostic in context, then inspect the characters before and after the reported area. Do not treat a syntax result as a complete explanation of every possible data problem.
Common mistakes
People often paste JavaScript notation with single quotes, comments, or trailing commas. Convert it to standard JSON rather than assuming similar-looking language syntax is interchangeable.
A valid result is sometimes mistaken for schema validation. Check required properties, value ranges, and permissions in the system that owns those rules.
Limits and special cases
The documented input is source text. The interface does not establish JSON Schema fields, business-rule validation, file processing, or a guarantee about every parser-specific edge case.
Duplicate keys, very large numbers, and downstream encoding deserve separate tests when their behavior matters to a consumer.
Examples
Accept a simple object
Is a basic object valid JSON?
Submit the complete object.
The source uses quoted names, a string, and a boolean in a valid object structure.
Reject an unquoted name
Why is an unquoted property name invalid?
Submit the source and inspect the failure.
Standard JSON requires the member name to be a double-quoted string.
Accept nested data
Can an object contain an array of objects?
Submit the nested value as one document.
The array, objects, numbers, commas, and brackets form valid JSON syntax.
Reject a trailing comma
What does a final comma do?
Submit the object with the final comma.
A trailing comma is not allowed by standard JSON. Remove it and validate again.
Keep null distinct
Is null a valid JSON value?
Submit the object and inspect the status.
null is a standard JSON value. Its meaning in an application is a separate decision.
Reject a missing closing bracket
Why must every opening bracket close?
Submit the unbalanced structure.
The array opens with [ but does not close with ]. Correct the nesting before using the data.
Frequently asked questions
Does valid JSON mean valid application data?
No. It means the text can be parsed as JSON. Required fields, types, ranges, and business rules need separate checks.
Can the validator repair my source?
Treat the validator as a checker. Correct the source yourself, then submit it again so the new text is checked.
Are comments allowed?
Not in standard JSON. Remove comments or use a documented preprocessing step that produces standard JSON.
Why are single quotes rejected?
Standard JSON strings and member names use double quotes. Single quotes belong to some programming-language syntaxes.
Does it check JSON Schema?
The source contract documents a JSON text field, not a Schema field. Do not describe schema validation without separate evidence.
Can a JSON array be the top-level value?
JSON can represent an array as a value. Submit a complete array and interpret the result according to the validator's documented grammar.
Are duplicate keys always rejected?
Do not assume a universal policy. Acceptance and the resulting value can depend on the parser, so test the consumer when duplicates matter.
What should I do after validation passes?
Run the checks your project requires, such as schema validation, authorization rules, value ranges, and integration tests.