Paste JSON above to get started
Try an example, or paste your own JSON above.
How to use the JSON Validator
- Paste or type your JSON into the input box.
- Tap Validate JSON to check it instantly.
- See whether it's valid, or get the exact error and location if not.
- Use the Copy or Share buttons to save or send your result.
Tip: If validation fails, look at the character position in the error message first — most JSON errors (a missing comma, an extra comma, or a missing quote) sit right before or after that position.
Common mistakes to avoid
- Using single quotes instead of double quotes around keys and string values.
- Leaving a trailing comma after the last item in an object or array.
- Forgetting to escape special characters like backslashes or quotes inside strings.
How the JSON Validator Works
Real parsing, not a guess
This tool runs your text through the browser's built-in JSON.parse() function — the same strict parser that JavaScript itself uses. If your JSON is valid, parsing succeeds silently. If it isn't, JSON.parse() throws a descriptive error that includes the character position where parsing broke down, which this tool surfaces directly instead of hiding it.
When to use this tool
Use it whenever you're debugging an API response, checking a hand-written config file, verifying JSON before pasting it into code, or troubleshooting a payload that a server or app is rejecting.
✓ Pros
- Works instantly, right in your browser
- Uses the same strict parser as JavaScript itself, so results match real-world behavior
- No sign-up, no ads blocking the result
✕ Limitations
- It validates syntax only — it can't tell you whether the data structure matches what your application expects.
- Very large JSON payloads (multiple megabytes) may take a moment to parse in the browser.
- It doesn't support JSON5 or JSONC (JSON with comments) — only strict, standard JSON.
Common JSON Errors Explained
What the error messages actually mean
JSON parser error messages can look cryptic at first, but they almost always point to one of a small handful of syntax problems. Here's what the most common ones mean and how to fix them.
Error message cheat sheet
- "Unexpected token" near a bracket: usually a trailing comma or a missing comma between items.
- "Unexpected end of JSON input": a bracket or brace was never closed — count your opening and closing
{}and[]pairs. - "Unexpected token" near a letter: a string value is missing its surrounding double quotes.
- "Bad control character": an unescaped newline or tab is sitting inside a string value.
Validating vs. Formatting
Validating and formatting are two different jobs. This tool only validates — it tells you whether your JSON is syntactically correct and, if not, exactly where it breaks. It deliberately doesn't try to auto-correct or reformat anything, because guessing at a fix could silently change your data's meaning. Once your JSON passes validation here, TickmarkTools' JSON Formatter can pretty-print it with consistent indentation for easier reading.
Quick Reference: Valid JSON Syntax
A quick refresher on what strict JSON requires, since it's stricter than JavaScript object syntax:
| Rule | Valid example | Invalid example |
|---|---|---|
Keys need double quotes | {"name": "Ali"} | {name: "Ali"} |
Strings need double quotes | "hello" | 'hello' |
No trailing commas | [1, 2, 3] | [1, 2, 3,] |
Booleans are lowercase | true / false | True / False |
No comments allowed | {"a": 1} | {"a": 1 // note} |
This tool enforces the strict JSON specification (RFC 8259) — the same rules used by JSON.parse() in every modern browser.
Features
Precise error location
Instant validation
No data stored
Mobile friendly
How TickmarkTools compares
An honest, feature-by-feature look at browser-based developer tools.
| Feature | TickmarkTools | Typical free sites | Premium suites |
|---|---|---|---|
| Price | Free | Free / freemium | Free tier + paid plans |
| Sign-up required | No | Often yes | Yes |
| Data leaves your device | Never | Usually | Usually |
| Watermark on export | None | Sometimes | On free tier |
| Mobile friendly | ✓ | Varies | ✓ |
| Works without account | ✓ | Varies | ✗ |
These are general, illustrative observations about common patterns across free online calculator tools as a category — not verified or benchmarked data about any specific named competitor or product. Individual sites vary and may differ from what's shown here.
Why you can trust this tool
No data stored
Your input is never saved or logged.
Secure processing
All processing happens client-side in your browser.
Fast processing
Results render in milliseconds, no waiting.
Mobile friendly
Use this tool from any device.
No sign-up
No account, no email, no watermark.
Works offline*
Once loaded, this tool needs no internet connection.
Accuracy & limitations
This tool checks JSON syntax accurately, but it's worth knowing what it doesn't do:
- Syntax only. A payload can be valid JSON and still have the wrong structure, missing fields, or wrong data types for your application — validate your schema separately if that matters.
- No auto-fix. The tool reports problems but never rewrites your JSON, so you stay in full control of any changes.
- Standard JSON only. Comments, trailing commas, and unquoted keys (allowed in JSON5/JSONC) will be flagged as errors here, by design.
JSON Validator FAQ
Yes, the JSON Validator is completely free with no sign-up required.
Trailing commas, single quotes instead of double quotes, missing quotes around keys, and unclosed brackets or braces are the most frequent causes.
No, it only validates and reports errors — use the JSON Formatter to auto-format your JSON once it's valid.
No. Standard JSON does not support comments of any kind — remove them before validating.
There's no hard limit, but extremely large JSON files (multiple megabytes) may take a moment to parse since everything runs in your browser.
No. All calculations run entirely in your browser, and nothing you enter is ever sent to a server or stored.
💡 Quick Help
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