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JSON Tools

JSON Validator Online

Check whether a string is valid JSON and see the parser error if it is not.

Updated

Ctrl/Cmd + Enter to run

Formatting changes whitespace only. JavaScript parsing can change very large integer precision, collapse duplicate keys, or reorder integer-like keys, so keep the original input when exact preservation matters.

This tool runs in your browser. No account or signup is required.

Common JSON Validator tasks

Developers typically reach for this page when they need to check if JSON is valid online; find a JSON syntax error; fix trailing comma in JSON. The tool is built for quick, practical work rather than a generic demo.

What matters in a json validator workflow

When developers compare online tools for this job, the useful capabilities tend to center on line-column errors, repair context, RFC language, local processing. This page keeps those practical needs in mind while linking to related tools when a different workflow is a better fit.

What is JSON Validator?

JSON Validator parses your text with the browser's own JSON parser and tells you whether it is valid JSON.

What problem does it solve?

A trailing comma, single quotes or an unescaped character breaks JSON.parse in production. Validating first tells you something is wrong before your app does.

How to use JSON Validator

  1. Paste your JSON into the input box.
  2. Press Process.
  3. You get "Valid JSON!" or the exact parser error message.

Example

Input

{"name": "Ada",}

Result

Error: (parser message about the unexpected "}" - wording depends on your browser)

What you can do with JSON Validator

  • Validate JSON online
  • Find a JSON syntax error
  • Check if JSON is valid

Common use cases

  • Checking a hand-edited config file
  • Debugging a 400 error caused by a bad request body
  • Validating JSON before importing it somewhere strict

Related developer tasks

  • Validate JSON online
  • Find a JSON syntax error
  • Check if JSON is valid

What counts as valid JSON

JSON (defined in RFC 8259) has seven kinds of value: object, array, string, number, true, false and null. Strings and keys use double quotes, items are separated by commas with no trailing comma, and comments are not allowed.

A bare value is valid too. The text "hello", 42 and null are each valid JSON documents on their own.

What this validator checks, and what it does not

  • It checks syntax only, using the browser's own JSON parser.
  • It does not check your data against a JSON Schema, so it cannot tell you that a field is missing or has the wrong type.
  • It reports the first error the parser hits. Fix it and press Process again to find the next one.
  • The wording of the error message depends on your browser, because each engine words its parse errors differently.

A quick validation workflow

Paste the JSON, press Process, and fix whatever the error points at. Once it reads Valid JSON, format it so the structure is easy to read, or minify it if you need a compact string.

Next steps: JSON Formatter, JSON Minifier, JSON to C#

JSON Validator FAQ

What makes JSON invalid?

Common causes are trailing commas, single quotes instead of double quotes, unquoted keys, and comments. Strict JSON allows none of these.

Does formatting preserve my JSON exactly?

Formatting changes whitespace, but this tool uses JavaScript JSON.parse and JSON.stringify. Very large integers can lose precision, duplicate object keys keep only the last value, and integer-like keys can be reordered. Keep the original input when exact preservation matters.

Is my data sent to a server?

The processing runs in your browser, so what you paste into the tool is not uploaded for processing. As with any tool, avoid pasting live secrets you cannot afford to leak.

Does it validate against a JSON Schema?

No. It checks that the text is syntactically valid JSON. Schema validation needs a schema and a schema-aware validator.

Why does it only show one error?

JSON.parse stops at the first problem it finds. Fix that one and validate again to reveal the next.

Is a plain string or number valid JSON?

Yes. Under the current standard any JSON value can appear at the top level, so "hello" and 42 are both valid.

Looking for something else? Browse all developer tools.

onlinedevelopertool.com is a collection of 54 free, browser-based utilities for the small jobs that interrupt real work: formatting a JSON response, decoding a token, converting a timestamp, generating a UUID or checking a hash. Each tool has its own page with a short explanation, a worked example and answers to common questions, so you can use it and learn what it does at the same time.

There is no account to create and nothing to install. Tools run in your browser, so the text you paste is processed on your own device. The one exception is the Website Status Checker, which sends a request from your browser to the address you enter.

Three steps: paste your input, click the tool, copy the result, all inside your browser
Popular developer utilities: JWT decoder, UUID generator, Base64 decoder, SHA-256 hash, regex tester and timestamp converter

What you can do here

  • JSON Tools

    Format, validate, beautify and minify JSON, generate C#, TypeScript, Java, Python, Go, PHP and Kotlin models from it, or convert between JSON, YAML and CSV.

  • Encoders & Decoders

    URL, Base64 and HTML encoding and decoding, plus a JWT decoder for reading token claims.

  • Generators & Hashes

    Generate UUIDs and JWTs, validate UUIDs, and create MD5, SHA-256 and SHA-512 hashes.

  • Web Tools

    Timestamps, color codes, query strings and cron expressions - the small things web work keeps throwing at you.

  • Text & Data

    Format XML and YAML, count text, change case, make slugs, test regex, diff two texts and convert number bases.

  • Website Checking

    Check whether a website or URL is reachable from your browser.

Quick developer reference

  • JSON

    Keys and strings must use double quotes, and trailing commas and comments are not allowed. Those are the three most common reasons a payload fails to parse.

    Validate JSON

  • JWT

    A JSON Web Token is three Base64URL parts joined by dots: header, payload and signature. Decoding shows the claims but does not prove the token is genuine; only signature verification does.

    Decode a JWT

  • Base64

    Base64 is an encoding, not encryption. Anyone can reverse it, and it makes data roughly one third larger, so never use it to hide secrets.

    Decode Base64

  • UUID

    A version 4 UUID is made of random bits and written as 8-4-4-4-12 hexadecimal characters. Collisions are astronomically unlikely, which is why they work well as identifiers.

    Generate a UUID

  • Timestamps

    A Unix timestamp counts time since 1 January 1970 UTC. Ten digits usually means seconds and thirteen digits usually means milliseconds.

    Convert a timestamp

  • Hashes

    MD5 is fine for quick checksums but is not safe for security. Prefer SHA-256 or SHA-512, and remember that hashing is one-way and is not encryption.

    Create a SHA-256 hash

Missing a tool you need? Visit the contact page and tell us what you reach for most often. You can also browse every tool or read the About page to see how the site is built and what it does with your data.