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.

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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.

CIDR / Subnet Calculator — Calculate Subnet Details Online

CIDR / Subnet Calculator takes an IPv4 CIDR block (e.g. 192.168.1.0/24) and computes: network address, subnet mask, wildcard mask, broadcast address, first and last usable host, number of usable hosts, IP class, and whether the address is in a private RFC 1918 range. It also displays the subnet mask in binary for visualising the prefix boundary. All calculation runs in the browser with no server communication.

Understanding CIDR and Subnetting

Before CIDR (introduced in 1993), IP addresses were divided into fixed classes: Class A (/8, 16.7M hosts), Class B (/16, 65K hosts), Class C (/24, 254 hosts). This was wasteful — an organisation needing 1000 hosts had to take a Class B (65K addresses) because Class C was too small. CIDR replaced classes with a variable-length prefix that can be any value from /0 to /32, allowing exact-fit allocation.

A subnet is a logical subdivision of a larger network. In a /24 network (256 addresses), you might carve out a /26 (64 addresses) for web servers, a /27 (32 addresses) for database servers, and reserve the rest for future use. Cloud providers use this extensively: AWS VPCs are typically /16 or /24, with individual subnets as /24 or /28 per availability zone.

The subnet mask encodes the prefix in dotted-decimal: a /24 prefix means the first 24 bits are 1s, or 11111111.11111111.11111111.00000000 = 255.255.255.0. A /19 prefix is 11111111.11111111.11100000.00000000 = 255.255.224.0. Routers use the mask to determine whether a destination IP is on the local network (AND with mask = network address) or must be forwarded.

Common Subnet Sizes Reference

/32 — Single host (1 IP). Used in host routes and /32 security group rules. /31 — Point-to-point links (2 IPs, RFC 3021). No broadcast or network address in /31. /30 — 4 IPs, 2 usable. Classic WAN link size. /29 — 8 IPs, 6 usable. Smallest typical customer allocation. /28 — 16 IPs, 14 usable. AWS minimum subnet size. /27 — 32 IPs, 30 usable. /26 — 64 IPs, 62 usable. /25 — 128 IPs, 126 usable. /24 — 256 IPs, 254 usable. The most common subnet in LANs and cloud VPCs.

/23 — 512 IPs, 510 usable. /22 — 1024 IPs, 1022 usable. /21 — 2048 IPs, 2046 usable. /20 — 4096 IPs. /16 — 65536 IPs. Typical VPC size. /10 — 4.2M IPs. /8 — 16.7M IPs. Class A range. Note: /0 covers the entire IPv4 address space (0.0.0.0/0), used in default routes.

Common Use Cases

Planning IP address allocation for VPC subnets in AWS, GCP, or Azure
Verifying firewall rules and security group CIDR ranges
Designing network topologies for on-premises infrastructure
Learning subnetting and binary mask calculations
Checking whether two IP addresses are in the same subnet

Frequently Asked Questions

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation represents an IP address and a network prefix length as a single string: IP/prefix, e.g. 10.0.0.0/8. The prefix length (0–32) specifies how many leading bits are fixed (the network part); the remaining bits are free (the host part).

How many hosts does a /24 subnet have?

A /24 subnet has 2^(32-24) = 256 total IP addresses. Two are reserved: the network address (e.g. 192.168.1.0) and the broadcast address (192.168.1.255). That leaves 254 usable host addresses.

What is the difference between subnet mask and wildcard mask?

The subnet mask has 1s for the network bits and 0s for the host bits (e.g. 255.255.255.0 for /24). The wildcard mask is the bitwise inverse: 0s for the network bits and 1s for the host bits (e.g. 0.0.0.255 for /24). Wildcard masks are used in Cisco ACLs and OSPF area definitions.

What are the private IP address ranges?

RFC 1918 defines three private ranges: 10.0.0.0/8 (Class A, 16.7M addresses), 172.16.0.0/12 (Class B, 1M addresses), and 192.168.0.0/16 (Class C, 65K addresses). These addresses are not routed on the public internet and are used in private networks and cloud VPCs.

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.

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