JSON Validator Online

What is JSON Validation?

JSON validation — also called JSON linting or JSON syntax checking — is the process of verifying a JSON string against the RFC 8259 specification. A JSON checker parses every bracket, comma, quote, and data type and flags anything that violates the standard. When it finds a JSON syntax error it reports the exact position so you can fix it immediately — without scanning hundreds of lines manually.

This is distinct from formatting: a JSON formatter makes valid JSON human-readable by adding indentation. A validator tells you whether your JSON is valid in the first place. Always validate first, then format.

JSON Validation Rules — RFC 8259

The JSON specification (RFC 8259) defines six hard rules. Violating any one of them produces a syntax error that prevents parsing.

Why JSON Validation Matters

Features of This JSON Validator

• my_locationPrecise error location — reports the exact line number and character position of every syntax error.
• boltAuto-validate on paste — paste JSON and the validator runs immediately, no button click needed.
• lock100% client-side — your JSON never leaves the browser. Safe for API keys, tokens, and sensitive payloads.
• analyticsStructure analysis — on valid JSON shows type, total key count, nesting depth, and top-level item count.
• keyboardKeyboard shortcut — press Ctrl+Enter (or Cmd+Enter on Mac) to validate without reaching for the mouse.
• volunteer_activismCompletely free — no account, no rate limits, no paywalls. Use it as many times as needed.

JSON Validator Example

Here is what valid vs invalid output looks like when you paste JSON into the validator above:

{"name": "John", "age": 30,}

{"name": "John", "age": 30}

How to Validate JSON Online — Step by Step

JSON Validator vs Formatter vs Linter

These tools are related but solve different problems. The typical workflow is: validate → fix errors → format.

JSON Schema Validation vs Syntax Validation

There are two distinct levels of JSON validation that developers often confuse:

// Always valid syntax:
{"age": "thirty"} // ✓ well-formed
{"age": 30}       // ✓ well-formed

// Schema says age must be number:
{"age": "thirty"} // ✗ type mismatch
{"age": 30}       // ✓ matches schema

Use this tool for syntax validation. For schema-level type checking, integrate Ajv or a JSON Schema validator into your build pipeline.

Common JSON Errors & How to Fix Them

These five errors account for the vast majority of invalid JSON. Paste your JSON into the validator to detect them automatically.

JSON Error Messages Decoded

Every JSON.parse() error message tells you exactly what went wrong — if you know how to read it. Here is a reference for the most common JSON parse errors:

Paste your JSON above and the validator will show you the exact error message — then match it to this table to find the fix instantly.

API Response Validation Workflow

One of the most common uses of a JSON validator is validating API responses. Malformed JSON from a third-party API causes silent failures and 500 errors that are notoriously hard to debug. Here is a bulletproof workflow:

// Or capture it in code before parsing:
const raw = await response.text(); // NOT response.json()
console.log(raw); // paste this into the validator

// Check the Content-Type header:
fetch('/api/data')
  .then(r => { console.log(r.headers.get('content-type')); return r.text(); })
  .then(raw => console.log(raw.slice(0, 200))); // log first 200 chars

async function safeJsonFetch(url: string) {
  const res = await fetch(url);
  const text = await res.text();
  try {
    return JSON.parse(text);
  } catch {
    throw new Error(`Invalid JSON from ${url}: ${text.slice(0, 100)}`);
  }
}

Validate JSON in Your Language

Every major language has a built-in JSON parser that throws on invalid input. Use these snippets to validate JSON programmatically — or use this tool for a faster interactive check.

try {
  const data = JSON.parse(jsonString);
  console.log('Valid JSON:', data);
} catch (e) {
  console.error('Invalid JSON:', e.message);
}

import json
try:
    data = json.loads(json_string)
    print('Valid JSON:', data)
except json.JSONDecodeError as e:
    print('Invalid JSON:', e)

import "encoding/json"

var result interface{}
if err := json.Unmarshal([]byte(jsonStr), &result); err != nil {
    fmt.Println("Invalid JSON:", err)
}

# Validate a JSON file from the terminal
node -e "JSON.parse(require('fs').readFileSync('file.json','utf8')); console.log('Valid')"

# Validate a JSON file using Python's built-in tool
python3 -m json.tool file.json > /dev/null && echo "Valid"

JSON5, JSONC & Comments in JSON

Standard JSON does not support comments, trailing commas, or unquoted keys. If your file has these features, it is one of these extended formats:

Rule of thumb: if a file is consumed by an API or JSON.parse(), it must be valid standard JSON. If it's a developer-facing config file (tsconfig, .eslintrc, VS Code settings), JSONC or JSON5 may be acceptable depending on the tool.

Validate JSON in CI/CD Pipelines

Automate JSON validation in your build pipeline to catch errors before they reach production. A failed JSON parse in a CI check is infinitely cheaper than a production 500 error.

- name: Validate JSON files
  run: |
    for f in **/*.json; do
      python3 -m json.tool "$f" > /dev/null && echo "✓ $f"
    done

"scripts": {
  "validate:json": "node -e \"['config.json','data.json'].forEach(f => { JSON.parse(require('fs').readFileSync(f)); console.log('✓', f); })\""
}

# jq is the fastest JSON validator in shell scripts
cat api-response.json | jq . > /dev/null && echo "Valid" || echo "Invalid"

Related JSON Tools

Frequently Asked Questions