What makes JSON invalid?

The most common causes are: trailing commas after the last key or array element, single-quoted strings instead of double-quoted, unquoted object keys, missing commas between items, and unmatched brackets or braces.

Does this validator send my JSON to a server?

No. Validation runs entirely in your browser using the built-in JSON.parse function. Your JSON data is never transmitted anywhere.

Why does the error point to the wrong line?

JSON.parse stops at the first syntax error it encounters. That error position may be downstream of the actual mistake — for example, a missing comma on line 3 may only surface as a parse error on line 5 when the parser finds an unexpected token.

What is the maximum file size?

The validator accepts files up to 10 MB. Larger files may slow down the editor but validation itself is fast since it uses the native JSON.parse implementation.

How is this different from a JSON Formatter?

A JSON Formatter transforms your JSON (pretty-prints or minifies it). This Validator only checks whether JSON is syntactically correct and reports errors — it does not change your JSON.

JSON Validator

Validate JSON syntax instantly. Get precise error messages with line numbers — your data never leaves your browser.

Last updated: April 2026

JSON Input

upload_fileUpload

Paste JSON here, upload a file, or click Sample

or drag & drop a .json file

infoReady — paste or upload JSON to validate

What it does

Real-time validation

Validation triggers automatically 300 ms after you stop typing, giving instant feedback without interrupting your editing flow.

Precise error locations

Error messages include the exact line number and column so you can jump straight to the problem — no guessing.

Monaco editor with squiggly underlines

The embedded Monaco editor (same engine as VS Code) renders red squiggly underlines at the exact error position in your JSON.

Auto-fix trailing commas

One click removes trailing commas from objects and arrays — the most common reason valid-looking JSON fails to parse.

File upload support

Drag and drop or browse for .json files up to 10 MB. The validator handles large files without blocking the browser UI.

JSON analysis stats

When JSON is valid, the results panel shows object count, array count, total properties, maximum nesting depth, and file size.

How to use JSON Validator

1
Paste your JSON
Click the editor and paste your JSON text, or drag and drop a .json file onto the editor area.
2
Read the real-time result
Validation runs automatically as you type (300 ms debounce). A green card means valid JSON; a red card shows the exact line and column of the first error.
3
Fix errors with guidance
The error message explains what is wrong and where. The Monaco editor underlines the error position. Click Auto-Fix to automatically remove trailing commas.
4
Review the analysis
When JSON is valid, the stats panel shows object count, array count, property count, nesting depth, and file size.

When to use this

Debugging API responses

Paste a raw API response to confirm it is valid JSON before writing parsing logic.

Fixing config files

Validate package.json, tsconfig.json, or other JSON config files that fail to load with an unhelpful error.

Checking generated JSON

Verify JSON output from scripts, templates, or code generators before deploying to production.

Learning JSON syntax

Use the precise error messages to understand exactly which JSON rules your input violates.

Common errors & fixes

Trailing comma — e.g. {"key": "value",}: Remove the comma after the last item in an object or array. Use the Auto-Fix button to remove all trailing commas automatically.
Missing quotes around a key — e.g. {key: "value"}: JSON requires all object keys to be double-quoted strings. Change key to "key".
Unclosed bracket or brace: Check that every { has a matching } and every [ has a matching ]. The error line number points to where the parser gave up, not always to the unclosed bracket.
Invalid escape sequence — e.g. "C:\Users\name": In JSON strings, backslashes must be escaped as \\. Use "C:\\Users\\name" or forward slashes "C:/Users/name".
Single-quoted string — e.g. {'key': 'value'}: JSON only accepts double quotes. Replace single quotes with double quotes throughout.

Why JSON validation is not the same as JSON formatting

Many developers reach for a JSON formatter when they actually need a validator. Formatters reindent your JSON and make it readable — but they also silently parse and re-serialise it, which means a formatter can mask errors by reformatting only the valid parts, or fail entirely without explaining why.

A dedicated validator's job is different: it reports exactly why your JSON failed to parse, at which line and column, with an explanation of what token was expected. This is the information you need when debugging an API integration, a config file that won't load, or JSON output from a code generator.

Another key difference is what happens with auto-fix. A formatter that auto-fixes trailing commas is making a silent editorial decision about your data. A validator makes the problem visible first and lets you confirm the fix — which is more appropriate when you are auditing data from an untrusted source.

Common JSON pitfalls and how to avoid them

Trailing commas are the single most common JSON error, especially for developers who write JavaScript daily. JavaScript objects and arrays allow trailing commas; JSON does not. The mismatch bites when JSON is written by hand or generated by JavaScript templating code.

The second most common error is single-quoted strings. JSON mandates double quotes for both keys and string values. JavaScript's loose syntax accepts single quotes, but any JSON parser will reject them. If you use a template literal or a JavaScript object literal to generate JSON, you need JSON.stringify() to produce valid output — not manual string concatenation.

Backslash escaping is the third common pitfall. In JSON strings, backslashes must themselves be escaped: a Windows path like C:\Users\name must be written as "C:\\Users\\name". Forgetting this is easy when copying paths from a file dialog or terminal output.

Frequently Asked Questions

What makes JSON invalid?: The most common causes are: trailing commas after the last key or array element, single-quoted strings instead of double-quoted, unquoted object keys, missing commas between items, and unmatched brackets or braces.
Does this validator send my JSON to a server?: No. Validation runs entirely in your browser using the built-in JSON.parse function. Your JSON data is never transmitted anywhere.
Why does the error point to the wrong line?: JSON.parse stops at the first syntax error it encounters. That error position may be downstream of the actual mistake — for example, a missing comma on line 3 may only surface as a parse error on line 5 when the parser finds an unexpected token.
What is the maximum file size?: The validator accepts files up to 10 MB. Larger files may slow down the editor but validation itself is fast since it uses the native JSON.parse implementation.
How is this different from a JSON Formatter?: A JSON Formatter transforms your JSON (pretty-prints or minifies it). This Validator only checks whether JSON is syntactically correct and reports errors — it does not change your JSON.