JSON Validator
Check JSON for syntax errors and see the reason.
How to use JSON Validator
Validate JSON and see the exact reason when it is invalid. No upload, fully private.
Open JSON Validator on toolpermarket — the form is ready, so type your numbers and read the result.
In the Input field, paste the JSON you want checked against the spec. Pair it with a schema only if you have one; syntax check works without.
In the Schema (optional) field, paste a JSON Schema to enforce structure, types and required fields. Leave schema blank for a pure syntax and shape check.
Press Validate to compute the result. The output appears immediately below the form. Edit a value and press the button once more to see the updated answer.
Read the result and use it as needed. If the number looks off, re-check your inputs and run it again — the math is deterministic, so the same entries always return the same answer.
Worked example. Validating {"name":"Ada","age":36} against a schema requiring age as integer passes; sending age:"36" fails with a type error.
Tips for accurate results.
Validate API responses in CI to catch contract drift early.
Read the first error — validators stop or report the earliest issue.
Use schema mode to enforce required keys, not just syntax.
When to use JSON Validator. Catching malformed JSON before it reaches code. Enforcing an API contract in tests or pipelines. Teaching teammates the expected shape of a payload.
When you actually reach for this
- An API or build step rejected your JSON and you need to find the exact line and character of the syntax error.
- You want to confirm a config file is well-formed before committing or deploying it.
Where this tool stops being accurate
- It only checks syntax, not schema — valid JSON can still have the wrong shape or missing fields for your use case.
- Comments and trailing commas are not valid JSON; the validator will report them as errors even though some parsers allow them.
Frequently asked questions
What is the difference between validate and format?
Formatting only checks that the text is syntactically valid JSON and reorganizes whitespace; validation goes further and compares the data against a JSON Schema, confirming types, required fields, value ranges and nesting. Use format to clean, use validate to enforce a contract.
Do I need a schema to use it?
No. Without a schema the tool still performs a strict parse that rejects any malformed JSON and reports where it broke. The schema is optional and only adds structural rules such as "age must be a number" or "email is required".
Why did validation pass but my code still failed?
A schema only checks what you told it to check. If a field is missing from the schema it is not enforced, and runtime code may expect more than the schema demands. Treat validation as a floor, not a guarantee that every downstream consumer will be satisfied.
The error says "unexpected token" but I cannot see it — how do I find it?
Look at the reported line and column: the culprit is usually a missing comma before it, a trailing comma, or an unquoted key just before that position.
My file has comments and still works in Node — why does validation fail?
Node uses JSONC for some configs; strict JSON forbids comments and trailing commas. Remove them for standard JSON, or use a JSONC validator.