JSON Validator — Check if JSON is Valid Online

What is JSON Validator?

A JSON validator checks whether a text document conforms to the JSON grammar defined by RFC 8259 (ECMA-404). Unlike a formatter, which reshapes valid JSON into a readable layout, a validator answers a single, non-negotiable question: is this JSON syntactically legal? For any error it reports the exact line, column, and cause — critical when debugging an API payload, a CI config, or a webhook body. This page also surfaces structure statistics that make it easier to reason about unfamiliar payloads at a glance.

How to validate JSON online

1. 1Paste your JSON into the input editor on the left.
2. 2The status card on the right turns green (Valid) or red (Invalid) immediately.
3. 3If invalid, the exact line and column of the first syntax error are shown, along with the parser message.
4. 4If valid, the tool reports the root type, max depth, key count, node count, and a breakdown by JSON type.
5. 5Fix the error at the reported position and re-validate — no upload, no page reload required.

Use Cases

Code Examples

function isValidJson(input) {
  try {
    JSON.parse(input);
    return true;
  } catch (err) {
    console.error(err.message); // includes position on modern V8
    return false;
  }
}

import json

def is_valid_json(s: str) -> bool:
    try:
        json.loads(s)
        return True
    except json.JSONDecodeError as e:
        print(f"error at line {e.lineno}, col {e.colno}: {e.msg}")
        return False

# jq exits non-zero on invalid JSON
echo "$payload" | jq empty && echo "valid" || echo "invalid"

import "encoding/json"

func isValidJSON(data []byte) bool {
    return json.Valid(data)
}

Key Concepts

RFC 8259

The current authoritative JSON specification. Defines the six structural characters { } [ ] , : and the three literals true / false / null.

Strict vs lenient parsing

Strict parsers (JSON.parse, encoding/json, Python's json module) follow RFC 8259 to the letter. Lenient ones (JSON5, JSONC) allow comments, trailing commas, and unquoted keys.

Well-formed vs valid

Well-formed means syntactically parseable. Valid, in a JSON Schema context, means the parsed document also matches a declared shape. This tool checks the first, not the second.

Root type

JSON documents can have any of six root types — object, array, string, number, boolean, null. Older RFC 4627 only allowed object or array; RFC 8259 lifted that restriction.

Tips & Best Practices

• ▸Trailing commas are the #1 cause of 'unexpected token' errors — remove the comma after the last element of an array or object.
• ▸Keys are always strings in double quotes. `{ name: "x" }` is JavaScript, not JSON.
• ▸Standard JSON has no comments. If you need them, use JSON5 or JSONC and strip them before feeding into a strict parser.
• ▸JSON numbers may not be NaN or Infinity. Serialize special floats as null or a sentinel string.
• ▸For large payloads, prefer streaming validators (`stream-json` in Node, `ijson` in Python) — they detect errors without loading the whole document into memory.