How do I decode a Base64 string online?

Paste your Base64 string into SmartDevBox at smartdevbox.com. It automatically detects Base64 encoding and decodes it instantly — no configuration needed.

How do I decode a JWT token without a secret?

Paste your JWT token into SmartDevBox. The JWT Inspector tool decodes the header and payload and displays them as readable JSON. Note: this decodes but does not verify the signature — you don't need the secret to read the claims.

How do I format or pretty-print JSON?

Paste your minified or unformatted JSON into SmartDevBox. The JSON Formatter tool detects it automatically and pretty-prints it with configurable indentation.

How do I convert a Unix timestamp to a human-readable date?

Paste a Unix timestamp (e.g. 1700000000) into SmartDevBox. The Unix Timestamp converter detects it and shows the equivalent date and time in UTC and your local timezone.

How do I convert JSON to CSV?

Paste a JSON array of objects into SmartDevBox and select the JSON → CSV tool. It converts your data to comma-separated format with headers derived from the JSON keys.

How do I compute a SHA-256 hash online?

Use the Hash Generator tool on SmartDevBox. Paste any text and it computes MD5, SHA-1, SHA-256, and SHA-512 hashes simultaneously in the browser.

How do I parse and understand a cron expression?

Paste your cron expression (e.g. "0 9 * * 1-5") into SmartDevBox. The Cron Job Parser explains it in plain English and shows the next scheduled run times.

How do I decode an X.509 certificate online?

Paste a PEM-encoded certificate (beginning with -----BEGIN CERTIFICATE-----) into SmartDevBox. The Certificate Decoder extracts and displays the subject, issuer, validity dates, public key, and extensions.

Is SmartDevBox free to use?

Yes. SmartDevBox is completely free with no account or sign-up required. All tools run in the browser. An optional AI mode (for ambiguous input detection) can be enabled with your own OpenAI API key.

Does SmartDevBox send my data to a server?

No. All tools run entirely in the browser using client-side JavaScript. Your data never leaves your machine unless you opt into the AI mode, which sends input to OpenAI for format detection.

What is the best free online JSON formatter?

SmartDevBox automatically detects JSON when you paste it and formats it with configurable indentation. It also validates JSON and reports syntax errors with precise line and column numbers — all in the browser, free, with no account required.

What is the best free online Base64 decoder?

SmartDevBox auto-detects Base64 strings — including standard and URL-safe variants, with or without padding — and decodes them instantly on paste. No button to click, no tool to select.

How do I compare two JSON objects online?

Use the Split & Diff tool in SmartDevBox. Paste the first JSON in the left pane and the second in the right pane. Changes are highlighted line-by-line in real time.

Can I add my own tools to SmartDevBox?

Yes. SmartDevBox has a plugin system that lets developers register custom tools by providing a name, a detector function (returns a confidence score 0–1), and a transformer function. Custom tools appear in the sidebar alongside the 91 built-in tools and participate in auto-detection.

Does SmartDevBox work offline?

SmartDevBox is a Progressive Web App (PWA). All 91 tools run entirely client-side with no server dependency. Once the page is loaded, the tools work without an internet connection. AI mode requires connectivity.

JSON (JavaScript Object Notation) is a lightweight, human-readable text format for representing structured data. It was derived from JavaScript object literal syntax but is language-independent — parsers and generators exist in virtually every programming language. JSON is defined by RFC 8259 (ECMA-404).

What are the most common JSON syntax errors?

The most common JSON errors are: trailing commas after the last item in an object or array (not allowed in JSON, unlike JavaScript); single-quoted strings (JSON requires double quotes); unquoted keys; comments (JSON has no comment syntax); undefined or NaN values (not valid JSON values); and numbers with leading zeros (e.g. 007 is invalid).

Glossary

What Is JSON?

JSON (JavaScript Object Notation) is a lightweight, human-readable text format for representing structured data as key-value pairs, arrays, and nested objects. Despite the name, it is entirely language-independent and is the dominant data format for REST APIs, configuration files, and data storage across all modern programming languages.

The One-Line Definition

JSON is a text-based data interchange format defined by RFC 8259 (ECMA-404). It represents structured data using six value types: strings, numbers, booleans, null, objects, and arrays.

A JSON Example

{
  "user": {
    "id": 42,
    "name": "Ada Lovelace",
    "email": "ada@example.com",
    "active": true,
    "roles": ["admin", "editor"],
    "metadata": null
  }
}

JSON Data Types

JSON supports exactly six value types — no more, no less:

Type	Example	Notes
string	"Hello, world!"	Must use double quotes. Supports Unicode escape sequences (\uXXXX).
number	42 / 3.14 / -7 / 1e10	Integer or floating-point. No leading zeros, no NaN, no Infinity.
boolean	true / false	Lowercase only. Not "True" or 1/0.
null	null	Represents an absent or unknown value. Lowercase only.
object	{"key": "value"}	Unordered set of key-value pairs. Keys must be strings (double-quoted).
array	[1, "two", true, null]	Ordered list of any JSON values (mixed types are allowed).

Common JSON Syntax Errors

Because JSON is strict about syntax, small mistakes cause the entire document to fail to parse. These are the errors developers encounter most often:

Trailing commaInvalid: {"a": 1, "b": 2,}
Fix: Remove the comma after the last item. JSON (unlike JavaScript) does not allow trailing commas.

Single-quoted stringInvalid: {"a": 'hello'}
Fix: Use double quotes: {"a": "hello"}

Unquoted keyInvalid: {a: 1}
Fix: Keys must be double-quoted strings: {"a": 1}

CommentInvalid: {"a": 1 // comment}
Fix: JSON has no comment syntax. Remove comments before parsing.

undefined valueInvalid: {"a": undefined}
Fix: JSON has no undefined type. Use null, omit the key, or encode as a string.

Leading zero in numberInvalid: {"a": 007}
Fix: Leading zeros are invalid. Use 7 instead of 007.

JSON vs XML

JSON — compact, readableNo closing tags. Maps directly to objects and arrays in code. Smaller payload size. Dominant format for REST APIs. No support for attributes, namespaces, or comments.

XML — expressive, verboseSupports attributes, namespaces, comments, and mixed content. Used in SOAP services, SVG, HTML, and configuration files (pom.xml, web.xml). Larger payload for the same data.

Format or Validate JSON Now

Paste any JSON into SmartDevBox and it is auto-detected, formatted, and validated instantly — no button click. If there is a syntax error, the exact line and column number is reported. Open the JSON Formatter → or JSON Validator →

Frequently Asked Questions

What are the JSON data types?

Six: string (double-quoted), number, boolean (true/false), null, object ({key: value}), and array ([...]). There is no date, undefined, or function type in JSON.

What is the difference between JSON and XML?

JSON is more compact and maps directly to language data structures. XML supports attributes, namespaces, and comments, making it more expressive but more verbose. JSON dominates REST APIs; XML is common in SOAP and configuration files.

Can JSON have comments?

No. Standard JSON (RFC 8259) has no comment syntax. The JSON5 and JSONC formats add comment support but are not valid JSON.

How do I format and validate JSON online?

Paste your JSON into SmartDevBox. It auto-detects JSON input and pretty-prints it immediately. Syntax errors are reported with line and column numbers. 100% client-side — your data never leaves the browser.

What Is Base64 Encoding? →Binary data embedded in JSON (images, certificates) is typically Base64-encoded.

What Is a JWT? →JWT payloads are JSON objects encoded as Base64url strings.

JSON Formatter →Auto-detects and pretty-prints JSON with configurable indentation.

JSON to CSV Converter →Convert a JSON array of objects to CSV with one paste.