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.

IP Address Inspector — Analyze IPv4 & IPv6 Addresses Online

IP Address Inspector analyses any IPv4 or IPv6 address and returns: IP class (A/B/C/D/E for IPv4), private/public classification, loopback status, link-local status, multicast membership, the decimal integer representation, hexadecimal notation, and dotted-binary representation. Useful for understanding address properties at a glance without looking up RFC tables.

IPv4 Address Structure

An IPv4 address is a 32-bit number displayed in dotted-decimal notation: four 8-bit octets separated by dots (e.g. 192.168.0.1). The address space is divided into two logical parts: network bits (prefix) and host bits, determined by the subnet mask or CIDR prefix. Within the same subnet, devices communicate directly; across subnets, traffic is routed.

Special ranges include: 0.0.0.0/8 (this network), 10.0.0.0/8 (private — RFC 1918), 100.64.0.0/10 (shared address space — RFC 6598, used by ISPs for carrier-grade NAT), 127.0.0.0/8 (loopback — 127.0.0.1 is the standard loopback address), 169.254.0.0/16 (link-local / APIPA), 172.16.0.0/12 (private — RFC 1918), 192.168.0.0/16 (private — RFC 1918), 224.0.0.0/4 (multicast), 255.255.255.255/32 (limited broadcast).

The decimal integer representation (also called the network byte order integer) is computed as: (octet1 × 2^24) + (octet2 × 2^16) + (octet3 × 2^8) + octet4. This is useful for range comparisons without converting to binary. The hex representation prefixes the 8-digit hex value with 0x, which is often seen in C, low-level networking code, and packet captures.

IPv6 Address Structure

IPv6 addresses are 128 bits displayed as eight groups of four hexadecimal digits separated by colons (e.g. 2001:0db8:85a3:0000:0000:8a2e:0370:7334). Consecutive all-zero groups can be collapsed to :: (but only once per address). The ::1 loopback and :: unspecified addresses are important special cases.

IPv6 address types: Link-local addresses (fe80::/10) are auto-configured on all IPv6-capable interfaces and used for neighbor discovery; they are not routable. Multicast addresses (ff00::/8) replace IPv4 broadcast. Global unicast addresses (2000::/3) are routable on the public internet. Unique local addresses (fc00::/7) are the IPv6 equivalent of RFC 1918 private addresses.

Common Use Cases

Checking whether an IP from a log file is private or public
Verifying that a generated IP is in the expected class and range
Understanding the binary structure of an IP address for subnetting study
Debugging firewall rules by confirming address type classifications
Quickly checking if an IPv6 address is loopback, link-local, or multicast

Frequently Asked Questions

What are the IPv4 address classes?

Class A: first octet 1–126 (default mask /8, up to 16.7M hosts). Class B: first octet 128–191 (default mask /16, up to 65K hosts). Class C: first octet 192–223 (default mask /24, 254 hosts). Class D: first octet 224–239 (multicast). Class E: first octet 240–255 (reserved/experimental).

What is a link-local IPv4 address?

Link-local addresses (169.254.0.0/16) are automatically assigned when a device cannot obtain an address from a DHCP server. On Windows this is called APIPA (Automatic Private IP Addressing). A 169.254.x.x address usually means DHCP failed.

What does the IPv6 loopback address look like?

The IPv6 loopback address is ::1 (equivalent to 127.0.0.1 in IPv4). It refers to the local machine and never leaves the network interface.

Privacy & Security

This tool runs entirely in your browser using client-side JavaScript. No data is sent to a server — your input never leaves your machine. SmartDevBox has no account system, no usage tracking, and no paid tier. See the Privacy & Security page for full details.

CIDR / Subnet CalculatorCalculate subnet details from CIDR notation: network address, broadcast, host range, subnet mask, and usable hosts. Free, no sign-up, 100% client-side.
Random IP GeneratorGenerate random IPv4 addresses for testing and development. Free, no sign-up, 100% client-side.
String InspectorView character, word, line, sentence, byte, and Unicode statistics for any text. Free, no sign-up, 100% client-side.