JSON Validator

A JSON validator checks whether a text document follows standard JSON syntax rules (RFC 8259). It verifies double-quoted property names, correctly escaped strings, commas between values, colons between keys and values, balanced brackets and braces, and valid scalar types — before another application, API, or database consumes the document.

Paste your JSON into the input field, or open a local .json file. ToolsSonic parses the document in your browser using JSON.parse and immediately reports Valid JSON with document statistics, or Invalid JSON with the first error message, line number, column position, source context, and a targeted repair hint. Enable "Validate while typing" to get live feedback as you edit.

A JSON parse error means the browser's JSON.parse engine found a character that violates JSON syntax. Common causes include a missing comma between properties, a trailing comma before } or ], single quotes instead of double quotes, an unquoted key, an unfinished string, a JavaScript comment, an undefined or NaN value, or unbalanced brackets. The validator shows the error message, line and column, surrounding source context with a caret marker, and a specific repair hint for the most common patterns.

No. Standard JSON does not allow a trailing comma before a closing brace } or bracket ]. Trailing commas are valid in JavaScript object literals but JSON.parse rejects them. Remove the final comma, or use JSON Repair if the source is JavaScript-style with multiple extensions.

No. All JSON strings and property names must use double quotes. Single-quoted values are JavaScript syntax and are not accepted by JSON.parse or any RFC 8259 compliant parser.

No. Standard JSON does not define line comments (//) or block comments (/* */). If your configuration format supports comments (JSON5, JSONC, HJSON), remove them before validating strict JSON, or use a parser that targets that specific format.

ToolsSonic extracts the character offset from the browser's error message when the engine exposes one, then converts it to a line number and column, shows up to five surrounding lines, and places a caret under the reported character. Browser engines vary in error message format, so the location is a precise diagnostic aid rather than a guaranteed formal grammar position — but it correctly identifies the problem in the vast majority of real-world errors.

Yes. Copy the raw response body from your browser DevTools Network tab, a curl output, or an API client into the validator. ToolsSonic checks whether it is valid JSON before you pass it to JSON.parse, a database import, or a schema validator. Syntax validation confirms the format is correct — it does not check whether the response has the fields your application expects.

JSON syntax validation checks whether the document follows the JSON grammar: correct quotes, commas, brackets, and value types. JSON Schema validation checks whether a valid JSON document conforms to a defined schema — required properties, data types, value ranges, string patterns, and additional constraints. ToolsSonic's JSON Validator handles syntax. Use the JSON Schema Validator for schema conformance.

Native JSON.parse accepts duplicate object keys with implementation-defined last-value behavior rather than rejecting them as a syntax error. ToolsSonic reports what JSON.parse reports. If key uniqueness matters for your workflow, use a duplicate-key-aware parser or linter in addition to syntax validation.

After a valid parse, the Inspect structure tab shows the top-level type (Object, Array, String, Number, Boolean, or Null), total object keys, array items, maximum nesting depth, and counts of every scalar type (strings, numbers, booleans, nulls) across the entire document. It also lists the first 40 JSON paths so you can quickly see the shape of an API response or configuration file.

Yes. Click Open file and select a local .json or .txt file. The browser reads it with the FileReader API entirely in memory. The file is not sent to a server, no upload endpoint is contacted, and no data is written to localStorage or any persistent storage.

Yes. All validation uses the browser's built-in JSON.parse. There are no network requests, no upload endpoints, no analytics on your input, and no localStorage writes. Clipboard access is requested only when you click Paste. The validation report is generated and downloaded locally.

Use JSON Formatter to make the document readable with consistent indentation and optional key sorting. Use JSON Minifier to strip presentation whitespace for a transport payload. Use JSON Schema Validator to check required fields and data types. Use JSON Diff to compare it with another version. A passing syntax check confirms the document is structurally valid JSON — it does not guarantee that values are safe, complete, or semantically correct for your application.

JSONLint.com is a long-established online JSON validator that validates on form submission. ToolsSonic validates in real time as you type, shows a source context excerpt with a caret marker, provides targeted repair hints for the most common error patterns, and includes a structure inspection panel with type statistics and path preview. All processing is browser-only with no server submission required.