Are trailing commas valid in JSON?
No. {"a": 1, "b": 2,} and [1, 2, 3,] both fail JSON.parse. Trailing commas are legal in JavaScript object literals but forbidden by RFC 8259.
Paste JSON to validate syntax with JSON.parse in your browser—auto-check as you type, jump to errors, fix common JS-style issues, and copy formatted output. Nothing is uploaded.
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A JSON validator checks whether text conforms to the JSON specification (RFC 8259 / ECMA-404) and reports the line and column of the first syntax error—this tool runs JSON.parse locally in your browser.
JSON has strict syntax rules: keys must be double-quoted strings, values must be strings, numbers, objects, arrays, booleans, or null, and trailing commas are not allowed. A JSON validator parses input against these rules and returns pass or fail.
Unlike a JSON formatter (which beautifies valid JSON), a validator's primary job is detecting errors before `JSON.parse` runs in your app, CI pipeline, or API gateway. This tool auto-validates as you paste, shows line and column details, offers a context snippet with a caret, and can apply fix helpers for common JavaScript-isms (comments, trailing commas, unquoted keys).
This page validates **syntax only**—not JSON Schema contracts. Use JSON Schema Generator for structural validation after syntax passes.
Concise answers for common searches — definitions, steps, and comparisons.
No. {"a": 1, "b": 2,} and [1, 2, 3,] both fail JSON.parse. Trailing commas are legal in JavaScript object literals but forbidden by RFC 8259.
Yes. JSON.parse runs locally in your browser; payloads are not uploaded to EverydayTools servers. Verify in the Network tab while validating.
Checks JSON syntax with auto-validate, line/column errors, context snippets, fix helpers, and formatted local output—no upload required.
Paste or type JSON into the input area—or click Load sample. Auto-validation runs after a short debounce; very large payloads (>400k characters) require clicking Validate manually.
Valid JSON shows formatted output on the right. Invalid JSON displays an error message, line/column location, a context snippet, and a Jump to error button when position is available.
Edit manually or click Fix common errors to remove comments, trailing commas, and quote unquoted keys. Re-validate until status shows Valid JSON.
Copy formatted JSON or download validated.json. Use JSON Formatter for minify/indent control, JSON Diff to compare versions, or JSON Path Finder to explore keys.
Common real-world scenarios where this tool saves time.
Validate package.json, CI configs, and feature-flag JSON before deploy so runtime JSON.parse does not fail in production.
Paste webhook or REST request bodies that returned 400 errors to find the exact syntax mistake before retrying.
Use Fix common errors on object literals copied from code comments, trailing commas, or unquoted keys—then copy spec-compliant JSON.
Experiment with invalid examples and read line/column feedback to internalize RFC 8259 rules.
Step-by-step chains that connect related tools for common tasks.
Confirm syntax before prettifying or posting in PR comments.
Input
{"name": "Alice", "age": 30, "active": true}Output
✓ Valid JSON — formatted with 2-space indentAll keys are double-quoted, values use correct types, and there is no trailing comma.
Input
{"name": "Alice", "age": 30,}Output
✗ Invalid JSON at line 1, column 29Remove the comma after 30 or use Fix common errors to strip trailing commas automatically.
Input
{'name': 'Alice'}Output
✗ Invalid JSON at line 1, column 2JSON requires double quotes. Replace single quotes manually—Fix common errors does not rewrite quoted string delimiters.
Input
{ // user id
"id": 42, "active": true, }Output
✓ Valid after Fix common errorsComments and trailing commas are invalid in raw JSON but commonly appear in copied config snippets. Fix common errors strips them for a spec-compliant payload.
The tool runs JSON.parse on your input inside a Web Worker when available (sync fallback on the main thread). A successful parse produces formatted output via JSON.stringify with 2-space indent. SyntaxError messages are parsed for line, column, and byte position to build human-readable errors and context snippets.
Formula
JSON value → object | array | string | number | true | false | null
Object → { "key": value (, "key": value)* }
Array → [ value (, value)* ]Free online JSON syntax checkers for developers.
| Tool | Privacy | Auto-validate | Line/column errors | Fix helpers | Formatted output | Signup |
|---|---|---|---|---|---|---|
| EverydayTools | Browser-only — no upload | Yes (debounced) | Yes + context snippet | Comments, trailing commas, unquoted keys | Yes | No |
| JSONLint | Browser-only | Manual | Yes | No | Limited | No |
| JSONFormatter.org | Often server upload | Yes | Yes | Partial | Yes + tree view | Optional |
| CodeBeautify | Server upload common | Manual | Yes | Partial | Yes | Optional |
Where parsing happens affects privacy and verification.
| Factor | Browser-based (this tool) | Server-based validators |
|---|---|---|
| Privacy | JSON stays on your device | Payload uploaded to vendor |
| Verification | Network tab shows no JSON upload | Upload visible to vendor domain |
| Speed | No upload latency | Depends on bandwidth and queue |
| Large files | Limited by browser memory | Vendor size caps apply |
| Offline after load | Works once page loads | Requires internet for upload |
Use JSON Validator for syntax pass/fail and error location. Use JSON Formatter, Diff, or Path Finder after syntax is clean.
| Related tool | Use this tool when | Use related tool when |
|---|---|---|
| JSON Formatter | You need to know if JSON is syntactically valid and where the first parse error occurs. | JSON already parses and you want minify, custom indent, or a formatting-focused workflow. |
| JSON Diff | You are checking whether a payload parses before comparing versions. | Two JSON documents are valid and you need a structural diff after fixing syntax. |
| JSON Schema Generator | You need RFC 8259 syntax validation with line/column errors. | Syntax is valid and you need a schema contract for required fields and types. |
Run syntax check here before JSON Formatter when the source might include comments, trailing commas, or unquoted keys from JavaScript.
For production secrets, confirm the Network tab shows no upload requests while validating—browser-only processing is the default but worth verifying once.
Fix the first reported error only—JSON.parse stops at the first syntax error. Re-validate after each fix to find subsequent issues.
Replace ' with " manually. The fix helper targets comments, trailing commas, and unquoted keys only.
Pass syntax here first, then validate structure with JSON Schema Generator or your API's schema layer.
Use null instead of undefined; ensure numbers are finite. JSON.parse rejects non-JSON values.
Likely cause: Input exceeded 400,000 characters—the debounced auto-validate pauses to protect UI responsiveness.
Fix: Click Validate to run manually, or split the document and validate sections separately.
Likely cause: Some parsers accept JSON5 or trailing commas; strict RFC 8259 parsers reject them.
Fix: Ensure downstream systems use standard JSON.parse. Export formatted output from this tool for maximum compatibility.
Likely cause: Single-line minified JSON reports column numbers that are hard to scan visually.
Fix: After fixing syntax, open JSON Formatter to prettify—then edit multi-line output.
This tool checks syntax only. Use JSON Schema Generator after syntax passes to validate required fields and types.
Use JSON Path Finder or a dedicated tree viewer after validating syntax here.
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No. Validation runs entirely in JavaScript in your browser using JSON.parse. Your JSON—including API keys, tokens, and configs—never leaves your device during normal use.
Open Developer Tools → Network, filter by Fetch/XHR, paste and validate JSON on this page. You should see no requests carrying your payload—only static assets and the optional Web Worker script load from your origin.
This validator checks syntax only—quotes, commas, brackets, and valid value types. JSON Formatter beautifies or minifies already-valid JSON. JSON Schema validation (see JSON Schema Generator) checks whether valid JSON matches a structural contract—required fields, types, and ranges. A file can be valid JSON but fail Schema validation.
No. This page uses JSON.parse for syntax checking only. After syntax passes, use JSON Schema Generator or your application's schema validator for contract validation.
It removes // and /* */ comments outside strings, strips trailing commas before } or ], and quotes unquoted object keys. It does not convert single-quoted strings to double quotes—replace those manually. Always review output before production use.
Trailing commas after the last element in an object or array. JSON forbids them; JavaScript object literals allow them—causing confusion when copying from JS code.
Auto-validation pauses above 400,000 characters—click Validate to run manually. Payloads above ~100 KB may feel slower on low-memory devices because parsing runs in browser memory.
It debounces input by 250 ms after you stop typing. Empty input clears the result. Very large inputs skip auto-validate until you click Validate.
Yes. The layout is responsive with touch-friendly controls and a sticky status bar on mobile after you scroll. Long JSON may require vertical scrolling.
JSON.parse accepts duplicate keys—the last value wins per ECMAScript. This validator reports syntax validity, not duplicate-key semantics. Inspect parsed output manually if key uniqueness matters.
No. Those are JavaScript values, not JSON. Use null for absent values. Numbers must be finite—JSON.parse rejects NaN and Infinity.
Both check syntax locally in the browser. This tool adds auto-validate on paste, Web Worker parsing, fix helpers for comments/trailing commas, formatted output, and explicit privacy verification guidance. JSONLint focuses on classic line/column error display.
Yes—free with no signup, no watermark, and no usage limits for browser-based validation.
Yes. Paste the response body here to locate syntax errors before parsing in your application. If the body is HTML or plain text, fix the transport issue first—this tool expects JSON text.
Jump to error requires a byte position from the JavaScript engine error message. Some engines report line/column only—in that case use the context snippet and line number to edit manually.
JSON validation runs locally in your browser using JSON.parse in a Web Worker when supported. Payloads—including API keys, tokens, and configs—are not uploaded to EverydayTools servers during normal use.
Results match native JSON.parse behavior in modern Chromium, Firefox, and Safari for equivalent input. Fix helpers may change text before parse—review output before production.
Validation runs in client-side JavaScript (Web Worker with main-thread fallback). Open the Network tab while typing—no requests should contain your JSON body.
Open Developer Tools → Network, paste and validate JSON, and confirm no requests carry your payload. Cross-check a known-valid file against JSON.parse in your runtime.
Limitations: Syntax only—not JSON Schema validation. Fix helpers do not convert single-quoted strings. Auto-validate pauses above 400k characters. Very large JSON may be slow on low-memory mobile browsers.
Fix helpers are conveniences, not spec-compliant transforms. Verify output before sending to production APIs or storing as canonical config.
Part of Developer Tools
More free tools for the same workflow.
Free JSON Schema generator — paste sample JSON and instantly generate a JSON Schema Draft-7 with inferred types, required fields, and nested object definitions. No signup. Runs locally in your browser when supported—no upload required for normal use.
Free JSON path finder — click any value in a formatted JSON tree to instantly copy its JSONPath expression. Ideal for navigating deep API payloads and config files. No signup. Runs locally in your browser when supported—no upload required for normal use.
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Reviewed by EverydayTools Editorial Team on 2026-06-02.
Auto-validate on paste
Debounced JSON.parse in a Web Worker—syntax errors surface as you type without blocking the UI.
Line & column errors
See where JSON.parse failed, jump to the error, and preview a context snippet with a caret marker.
Runs locally
Your JSON stays in browser memory—nothing is uploaded. Verify in the Network tab while validating.
Removes // and /* */ comments, trailing commas, and quotes unquoted keys—review output before production use.