Data & Serialization · 100% Client-Side Browser Utility
Fast JSON Formatter, Online JSON Validator & Beautifier Tool. Check RFC 8259/7159/4627 syntax by line, inspect JSONPath trees, detect duplicate keys & fix locally.
JSON (JavaScript Object Notation, defined across IETF RFC 8259, RFC 7159, historical RFC 4627, and ECMA-404) powers REST and GraphQL APIs, OpenAPI / Swagger 3.0 contracts, PostgreSQL jsonb and MySQL JSON columns, and cloud configs. Strict JSON requires straight ASCII double quotes and forbids trailing commas, comments, and unescaped control characters.
The CrowdFeatures Online JSON Validator & Formatter lets you choose your JSON specification (RFC 8259, RFC 7159, RFC 4627, ECMA-404, or Skip Validation), load payloads by paste, drag-and-drop, or CORS-enabled URL, inspect exact line and column errors, detect duplicate keys, filter nodes via JSONPath ($.path) in Tree view, and repair broken JSON 100% locally in your browser.
Most JSON parse failures happen when JavaScript object literals, Python dictionaries, or escaped log strings are pasted into a strict RFC 8259 parser. Use the reference table below—or the interactive Auto-Correct and Remove Special Chars controls—to resolve them immediately.
| Validation Error | Invalid Example | Valid RFC 8259 JSON | Why & How to Fix |
|---|---|---|---|
| Trailing Comma | {"a": 1, "b": 2,} | {"a": 1, "b": 2} | RFC 8259 forbids a comma before closing } or ]. Click Auto-Correct to strip trailing commas. |
| Single Quotes / Unquoted Keys | {id: 'usr_1'} | {"id": "usr_1"} | All property names and strings must use straight ASCII double quotes (""). |
| Non-JSON Literals | {"ok": True, "val": None} | {"ok": true, "val": null} | Booleans and null must be lowercase true, false, or null. |
| Duplicate Object Keys | {"id": 1, "id": 2} | {"id": 1, "secondaryId": 2} | Standard JSON.parse silently overwrites earlier keys; our validator warns with exact line numbers. |
| Escaped Log Strings & Smart Quotes | "{\"msg\": “hello”}" | {"msg": "hello"} | Click Remove Special Chars to unescape \", \n, strip outer quotes, and normalize curly quotes. |
JSON Specifications Supported (RFC 8259, RFC 7159, RFC 4627, ECMA-404 & Skip Validation): Choose strict RFC 8259 (default), RFC 7159, RFC 4627 (requires top-level Object or Array), ECMA-404, or Skip Validation for best-effort recovery. Load payloads by pasting, dragging and dropping a .json file, or fetching a CORS-enabled URL directly in your browser.
Verified Privacy & Execution Architecture: All JSON validation (JSON.parse), formatting (JSON.stringify), duplicate-key scanning, Tree JSONPath filtering ($.path), and syntax repairs run 100% locally in your browser memory. Your JSON payload is never transmitted over the network. CrowdFeatures only records anonymous pageview and button-click counts (/api/analytics/track with route path and button label) to measure aggregate tool usage.
Related JSON & API Utilities: Convert JSON to YAML · Convert YAML to JSON · Decode JWT Payload JSON · OpenAPI & Swagger JSON Editor · Base64 Encode / Decode JSON
No. All JSON parsing (JSON.parse), beautifying (JSON.stringify), duplicate-key detection, JSONPath tree filtering, and syntax auto-correction run 100% locally in your browser memory. Your JSON text is never sent to a CrowdFeatures backend. CrowdFeatures only records anonymous pageview and button-click counters (route path and button label) to measure aggregate tool usage.
RFC 4627 (2006) required the top-level JSON root to be an Object ({...}) or Array ([...]). RFC 7159 (2014), ECMA-404, and the current RFC 8259 standard permit any JSON value (strings, numbers, booleans, null, objects, or arrays) at the root. Use the Spec selector in the toolbar to test compatibility or choose Skip Validation for best-effort recovery.
Unlike JavaScript objects, strict RFC 8259 JSON grammar prohibits a comma after the last item in an object or array and requires straight double quotes ("") around every property key and string value. Click 'Auto-Correct' in the toolbar to convert single quotes and strip trailing commas automatically.
Yes. Our validator scans every object scope and warns with the exact key name and line number when duplicate keys appear (which standard JSON.parse silently overwrites). Switch Output to 'Tree' view to browse branches, filter keys or values, and evaluate JSONPath queries such as $.endpoints[0].path.
Click 'Remove Special Chars' in the toolbar. It strips invisible UTF-8 byte-order marks (BOM), zero-width spaces, and ANSI terminal codes, normalizes curly smart quotes (“ ”) outside string literals, and unescapes stringified log payloads (such as \n, \t, and \").
Yes. Paste, drag-and-drop, or load any PostgreSQL jsonb value, MySQL JSON document, or OpenAPI / Swagger JSON specification to validate syntax, sort keys alphabetically (A–Z), inspect paths in Tree view, and beautify or minify the output.