5 Best Free JSON Tools Online (2025)

Why JSON Tools Matter

If you work with APIs, config files, or any modern web stack, you deal with JSON constantly. Raw JSON from an API response is often a wall of compressed text with no line breaks. Debugging a deeply nested object without proper formatting is painful. And converting structured data between formats by hand is a waste of time you could spend building things.

That is why having a reliable set of JSON tools bookmarked is a must. But instead of juggling five different sites with ads and cookie banners, you can use ToolBox — where every tool runs in your browser with zero tracking.

Here are the five JSON tools we think every developer should know about.

1. JSON Formatter & Validator

This is the one you will use daily. Paste in raw, minified, or messy JSON and get it instantly formatted with proper indentation. But formatting is only half of it — the tool also validates your JSON and shows you exactly where syntax errors are.

Key features:

- Auto-detects and highlights syntax errors with line numbers

- Adjustable indentation (2 spaces, 4 spaces, or tabs)

- Collapse and expand nested objects

- One-click copy of the formatted output

Common use case: You grab a response from `curl` or your browser's Network tab, paste it in, and immediately see the structure. If a trailing comma or missing bracket is hiding in there, the validator catches it before you waste 20 minutes hunting.

```json

// Before: a mess

{"users":[{"id":1,"name":"Alice","roles":["admin","editor"]},{"id":2,"name":"Bob","roles":["viewer"]}],"total":2}

// After: readable

{

"users": [

{

"id": 1,

"name": "Alice",

"roles": ["admin", "editor"]

},

{

"id": 2,

"name": "Bob",

"roles": ["viewer"]

}

],

"total": 2

}

```

Try the [JSON Formatter](/tools/json-formatter) on ToolBox.

2. JSON to CSV Converter

Sooner or later, someone on your team will ask for "the data in a spreadsheet." That means converting JSON arrays into CSV. Doing it manually for anything more than a handful of records is a non-starter.

Key features:

- Handles nested objects by flattening keys (e.g., `address.city`)

- Auto-detects array structures

- Customizable delimiter (comma, tab, semicolon)

- Download as .csv file

Common use case: Your API returns a JSON array of 500 user records. Product wants it in Google Sheets by end of day. Paste the JSON, click convert, download the CSV, done in 30 seconds.

Tip: If your JSON has inconsistent keys across objects, the converter fills missing fields with empty values so your CSV columns stay aligned.

Try the [JSON to CSV Converter](/tools/json-to-csv) on ToolBox.

3. JSON Diff Checker

When you are debugging why an API response changed between deployments, or comparing config files across environments, you need a diff tool that understands JSON structure — not just line-by-line text comparison.

Key features:

- Side-by-side comparison with color-coded differences

- Detects added, removed, and modified keys

- Handles reordered keys intelligently

- Works with large JSON documents

Common use case: You saved yesterday's API response and today's response looks different but you cannot tell what changed. Paste both into the Diff Checker and the differences light up immediately — maybe a new field was added, or a value changed from a string to a number.

```

Left: { "status": "active", "count": 42 }

Right: { "status": "inactive", "count": 42, "updatedAt": "2025-02-13" }

Result: "status" changed from "active" to "inactive"

"updatedAt" was added

```

Try the [Diff Checker](/tools/diff-checker) on ToolBox.

4. JWT Decoder (JSON Web Tokens)

JWTs are just Base64-encoded JSON with a signature. But decoding them by hand or remembering the `atob()` dance every time is tedious. A dedicated JWT decoder shows you the header, payload, and signature in seconds.

Key features:

- Decodes header and payload sections

- Shows expiration time in human-readable format

- Highlights expired tokens

- Never sends your token to a server

Common use case: A user reports they are getting 401 errors. They send you their JWT. You paste it into the decoder and immediately see the token expired 3 hours ago, or that the `aud` claim does not match your API's expected audience.

```

// Encoded

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4iLCJpYXQiOjE1MTYyMzkwMjJ9...

// Decoded Payload

{

"sub": "1234567890",

"name": "John",

"iat": 1516239022

}

```

The privacy angle matters here. You should never paste authentication tokens into random websites. Since ToolBox runs entirely client-side, your tokens stay in your browser.

Try the [JWT Decoder](/tools/jwt-decoder) on ToolBox.

5. Base64 Encoder/Decoder

While not exclusively a JSON tool, Base64 encoding comes up constantly in JSON workflows. API keys in config files, embedded images in JSON payloads, encoded query parameters — Base64 is everywhere.

Key features:

- Encode text to Base64 or decode Base64 to text

- Handles UTF-8 characters correctly

- File-to-Base64 conversion for images and documents

- Instant conversion as you type

Common use case: You are setting up a webhook and the provider wants your credentials as a Base64-encoded string in the JSON config. Or you receive a Base64 blob in an API response and need to see what is inside.

Try the [Base64 Encoder/Decoder](/tools/base64) on ToolBox.

Honorable Mentions

A few more tools that pair well with JSON workflows:

• Hash Generator — Generate MD5, SHA-1, SHA-256, and SHA-512 hashes of your JSON data for integrity checks
• URL Encoder/Decoder — When JSON lives inside URL parameters, you need to encode and decode it properly
• Regex Tester — Test regex patterns against JSON strings to extract or validate specific values

The Bottom Line

You do not need five different bookmarks for five different tools. ToolBox puts all of them in one place, running in your browser, with no accounts or tracking. Bookmark it once and you are set.

All tools mentioned in this article are free to use at [toolbox-kit.com](https://toolbox-kit.com).