Network tools built by
network engineers
Fast, free, and precise calculators for subnetting, CIDR planning, and IP addressing. No login. No fluff. Works entirely in your browser.
IPv4 Tools
CIDR Calculator
Enter any IPv4 CIDR block and instantly get network address, broadcast, subnet mask, wildcard mask, binary breakdown, and usable host range.
Open CIDR Calc →Subnet Tree Visualizer
Interactively visualize and split IPv4 subnets. Start with a parent block and recursively divide it into smaller subnets to plan your network hierarchy.
Open Tree Visualizer →VLSM Planner
Allocate subnets of varying sizes from a parent block. Enter host requirements and get network/broadcast/range for each — sorted and packed automatically.
Open VLSM Planner →Subnet Overlap Detector
Paste a list of CIDR blocks and instantly detect overlapping or duplicate networks. Essential for VPN and VPC peering rule audits.
Open Overlap Detector →IP Range → CIDR
Convert any arbitrary start–end IP range into the minimal set of CIDR blocks covering it exactly. Essential for firewall migrations and AWS Security Groups.
Open IP Range Converter →Mask Converter
3-way live converter between subnet mask, wildcard mask, and CIDR prefix. Full 33-row reference table. Type in any field — all others sync instantly.
Open Mask Converter →Bulk CIDR Aggregator
Clean, merge, and optimize large sets of IPv4 addresses or CIDR blocks. Handles thousands of entries to find the absolute minimal set of covering prefixes.
Open Bulk Aggregator →IPv4 Subnetting Quiz
Test your speed and accuracy. Practice calculating network addresses, broadcasts, and host counts under a timer. Perfect for CCNA/Network+ prep.
Open Subnet Quiz →IPv6 & Utilities
IPv6 Subnet Calculator
Enter any IPv6 prefix and get the network, first/last address, address count, and compressed/expanded forms.
Open IPv6 Calc →MTU & MSS Calculator
Calculate effective MTU and TCP MSS by accounting for encapsulation overheads like IPsec, VXLAN, and GRE.
Open MTU/MSS Calc →DNS Lookup (DoH)
Perform secure DNS-over-HTTPS queries for A, MX, TXT, and more directly from your browser using Cloudflare's 1.1.1.1 service.
Open DNS Lookup →SPF Record Generator
Interactive builder for Sender Policy Framework records. Configure mechanisms like A, MX, and Include with real-time validation.
Open SPF Generator →Certificate Decoder
Decode SSL/TLS X.509 certificates locally. Paste PEM or drop CRT/DER files to view SANs and expiration. 100% private.
Open Cert Decoder →Reference
Subnet Cheat Sheets
Instant reference tables for IPv4 prefixes, IPv6 allocation sizes, RFC 1918 private ranges, and wildcard masks.
Subnet Cheat Sheets →DNS Record Cheat Sheet
Quick reference guide for common DNS record types (A, MX, TXT, SRV, CAA) with examples and usage descriptions.
DNS Cheat Sheet →