What is JSON Validator?
JSON Validator is a browser-based tool that does two things: it checks whether your JSON is syntactically valid, reporting the exact line and column of any error, and it optionally validates the structure of valid JSON against a JSON Schema. Paste JSON alone to catch syntax mistakes, or add a schema to confirm the data has the right shape, types, and required fields.
JSON is the standard format for APIs, configuration, and data exchange, and a single misplaced comma or missing quote can break an entire integration. Beyond syntax, applications usually expect JSON to follow a specific contract — certain fields present, values of the right type, numbers within ranges. JSON Schema is the widely-used standard for describing and enforcing that contract.
Together, syntax checking and schema validation catch both classes of problem: malformed JSON that will not parse at all, and well-formed JSON that does not meet your requirements. Everything runs locally in your browser, so your JSON and schema — which may include real payloads and internal contracts — are never uploaded.
Why use JSON Validator?
When an integration fails, the first question is always "is the JSON even valid?" This tool answers it instantly and, crucially, points to the exact line and column of the first syntax error rather than just saying "invalid." That pinpoint accuracy turns a frustrating hunt through a large payload into a one-second fix.
Schema validation catches the subtler, more dangerous class of bug: JSON that parses fine but is structurally wrong. A response missing a required field, a string where a number was expected, or a value out of range will pass a basic syntax check but break your application. Validating against a schema confirms the data actually matches the contract your code depends on.
Doing this locally protects sensitive data. API payloads and schemas often reveal internal field names, business rules, and real customer data. This tool validates everything in your browser and sends nothing to a server, which you can confirm in the Network tab — so you can safely validate production data.
Features
- Checks JSON syntax and reports the exact line and column of errors
- Optionally validates structure against a JSON Schema
- Lists each schema violation with the path to the offending value
- Distinguishes a broken schema from data that fails the schema
- Prioritizes syntax errors before attempting schema checks
- Live validation as you type
- Clear pass/fail status messages
- Runs entirely in your browser — no uploads, works offline
How to use JSON Validator
- Paste the JSON you want to check into the JSON panel on the left.
- If the JSON is malformed, the result shows the error with its exact line and column.
- Optionally paste a JSON Schema into the schema panel to also validate the structure.
- Read the result: valid JSON, valid against the schema, or a list of specific schema violations with their paths.
- Fix the reported issues in the JSON (or the schema) and watch the result update live.
Example 1 — Catch a syntax error
A trailing comma is invalid JSON; the validator reports the precise location.
Input
{"a": 1,}Output
✗ Invalid JSON — line 1, column 9Example 2 — Validate against a schema
Valid JSON that violates a schema constraint is reported with the path to the problem.
Input
JSON: {"age": -5} · Schema: age must be an integer ≥ 0Output
✗ Valid JSON, but /age fails: must be >= 0Common Mistakes
- Trailing commas: JSON forbids a comma after the last element in an object or array. This is one of the most common syntax errors, often from copy-pasting JavaScript object literals.
- Single quotes and unquoted keys: JSON requires double quotes around all strings and property names. Single quotes or bare keys, which JavaScript allows, are invalid JSON.
- Confusing syntax validity with schema validity: JSON can be perfectly well-formed yet still wrong for your application. Valid syntax only means it parses; schema validation is what confirms the structure and types.
- A broken schema masquerading as a data problem: if the schema text itself is not valid JSON, the tool reports that specifically. Do not mistake a malformed schema for the data failing to match it.
- Expecting schema validation while the JSON is invalid: the tool checks syntax first and will not attempt schema validation on JSON that does not parse. Fix the syntax error before worrying about the schema.
- Comments in JSON: standard JSON has no comment syntax. If your file uses JSONC (like tsconfig.json), the comments must be stripped before it will validate.
Developer Tips
- Use this as the first diagnostic step when an API integration fails — confirming the payload is valid JSON (and matches the expected schema) quickly narrows down whether the problem is data or code.
- Keep a JSON Schema for each important API response and validate real responses against it; this catches contract drift — a field renamed, a type changed — before it causes runtime failures.
- When the validator reports a schema violation, the path it gives (like /user/age) points straight at the offending value, so you can jump to the exact field rather than searching.
- Format messy JSON with the JSON Formatter first if you want readable output, then validate it here — the two tools complement each other for cleaning and verifying payloads.
- Remember schema validation enforces structure and types but not business logic; some rules still need to be checked in your application code.
Frequently Asked Questions
- What is the difference between validating syntax and validating against a schema?
- Syntax validation checks only whether the text is well-formed JSON that a parser can read — correct quotes, commas, brackets, and so on. Schema validation goes much further: it checks that valid JSON also has the right structure, such as required fields being present, values being of the expected type, strings matching patterns, and numbers falling within allowed ranges. JSON can pass the syntax check but fail schema validation, which is exactly the kind of subtle bug that breaks applications even though the JSON "looks fine."
- What is a JSON Schema?
- A JSON Schema is itself a JSON document that describes the expected shape of other JSON data. It can specify which fields are required, what type each value should be (string, number, object, array, boolean), constraints like minimum and maximum for numbers or patterns for strings, and how nested structures should look. Validating data against a schema confirms it conforms to that contract. Schemas are widely used to document APIs and to automatically reject malformed requests and responses.
- Why does the validator show a line and column for errors?
- Pinpointing the exact position of the first syntax error is the fastest way to fix it. Rather than telling you the JSON is invalid and leaving you to search, the validator reports the line and column where parsing failed, so you can go straight to the problem — a missing comma, an extra bracket, or an unquoted key. In a large payload with hundreds of lines, this precise location is often the difference between a one-second fix and a tedious manual hunt.
- Is my JSON uploaded to a server?
- No. Both syntax checking and schema validation happen entirely in your browser using JavaScript. Your JSON and schema — which may contain real API payloads, internal field names, and business rules — are never sent to a server, logged, or stored. You can verify this by opening your browser's Network tab while validating: there are zero outbound requests, and the tool works even offline. This makes it safe to validate production data.
- What happens if my schema itself is invalid?
- The tool distinguishes between the two failure modes. If the schema text you paste is not itself valid JSON, it reports that specifically — telling you the schema is broken rather than pretending your data failed to match it. This prevents a confusing situation where a typo in the schema looks like a data problem. Fix the schema so it is valid JSON first, and then the validator can meaningfully check your data against it.
- How does this differ from the JSON Formatter?
- The JSON Formatter focuses on readability — pretty-printing or minifying JSON and reporting basic syntax errors. The JSON Validator focuses on correctness: it confirms the JSON is valid with precise error locations and, importantly, can validate the structure against a JSON Schema to check required fields, types, and value constraints. A common workflow is to format a messy payload first to make it readable, then validate it against a schema to confirm it meets the contract your application expects.