Network engineering tools that run entirely in your browser
Paste a network diagram, an address plan or a device configuration. Every calculation happens in this tab — there is no NetKit server to upload it to, and the tools keep working with no network at all.
- 24
- tools
- 6
- categories
- 0
- network calls
- No accounts, no uploads
- Installs as an app, works offline
- Every tool declares whether it uses the network
The pages carry Google’s advertising script, which funds the site. It is not part of the tools, and it is not given anything you type — what it does and does not see.
- Network
- 172.16.40.0/22
- Usable range
- 172.16.40.1 – 172.16.43.254
- Netmask
- 255.255.252.0
- Wildcard
- 0.0.3.255
- Usable hosts
- 1,022
- Addresses in block
- 1,024
- Reverse zone
- 0.40.16.172.in-addr.arpa
- Scope
- Private (RFC 1918)
Also a native app
NetSmith carries 34 tools on the phone — the same kernel, no account, one-time purchase.
It adds the three things a browser tab cannot do: the camera, for asset and serial stocktakes; real ICMP ping and traceroute from the phone you are actually standing in front of; and the live probes — DNS against any server, HTTP timing, TLS certificates and TCP port scans.
The tools
24 calculators, converters and references. No account, no upload.
Every one of them runs from the same kernel, in this tab, with no request of its own. Press ⌘K to search by name, keyword or pinyin initials.
10 tools
IP Addressing & Routing
Subnetting, VLSM planning, route summarization, IPv6 and address arithmetic.
- IPv4 Subnet CalculatorNetwork and broadcast address, usable host range, netmask and wildcard mask, host counts and the special-purpose classification for any address and prefix.Open
- Topology & Routing SimulatorDescribe a network as text, then trace a packet through it hop by hop: connected, static and single-area OSPF routes, longest-prefix forwarding, equal-cost multipath, and the exact hop where it dies when it does not arrive.Open
- VLSM Subnet PlannerSplit one block into right-sized VLANs: best-fit allocation for every host count, growth headroom, /31 point-to-point links, plus the leftover free blocks and a utilization figure.Open
- Route Summarization CalculatorReduce a list of prefixes to the minimal exact cover, the single covering supernet, and the holes that the supernet would advertise but nobody owns.Open
- BGP Aggregation & Suppress-Map BuilderBuild a BGP aggregate plan for Cisco, Huawei, Arista or Juniper: what summary-only suppresses, what must stay visible, and which routes fall outside the aggregate and would be blackholed.Open
- IPv6 Subnet CalculatorNetwork address, last address, total and usable address counts for any IPv6 prefix, with /127 point-to-point and /128 host-route handling, reverse-DNS zone and classification.Open
- IPv6 Address Compressor & ExpanderNormalize IPv6 addresses to the RFC 5952 canonical text form, expand them to eight full groups, and see the binary and hex-group forms side by side. One address per line.Open
- IPv6 Prefix SplitterSplit an IPv6 prefix into equal sub-prefixes: the subnet count, the first and last blocks, and a CSV export of the full list. The output is capped so large splits never freeze the tab.Open
- IPv6 EUI-64 ConverterDerive the EUI-64 interface identifier and link-local address from a MAC address, or work backwards from an interface identifier to the MAC, with the universal/local bit flip explained.Open
- IP Address Format ConverterRead an IPv4 address in any notation — dotted decimal, hex, dotted hex, decimal integer, octal or binary — and see all six representations plus the radix that was detected.Open
5 tools
Protocols & Standards
DHCP options, vendor TLVs, MAC and OUI handling, ASN formats, BGP regex.
- MAC Address Format ConverterPaste a MAC in any notation and get every convention back at once — Cisco, Linux, Windows, bare hex — plus the multicast and locally-administered bits and the EUI-64 / IPv6 link-local form.Open
- MAC OUI Vendor LookupPaste a MAC or a bare OUI and get the registered vendor, the assignment type (MA-L, MA-M or MA-S) and whether the address is globally unique or locally administered. Curated offline subset of the IEEE registry.Open
- ASN Format ConverterConvert an Autonomous System Number between asplain (4200000000) and asdot (64086.59904) in both directions, and see whether it is 16-bit or 32-bit, private, reserved or AS_TRANS.Open
- BGP AS-Path Regex TesterTest a BGP AS-path regular expression against a list of real AS paths, one answer per line. Expands the Cisco underscore metacharacter, explains each token in plain language and ships a preset library.Open
- DHCP Option 43 GeneratorBuild the DHCP option 43 value that points access points at their wireless controller, with the per-sub-option breakdown, the Cisco dotted hex, a per-vendor CLI, and a generic TLV builder for anything not covered.Open
4 tools
Cheatsheets
Ports, protocol numbers, header overhead and cross-vendor CLI equivalents.
- TCP/UDP Port LookupSearch TCP, UDP and SCTP port assignments by number, service name or purpose, with the IANA or vendor source and a confidence marker on every row.Open
- IP Protocol NumbersEvery assigned IANA IP protocol number with its registry keyword and RFC — ICMP 1, TCP 6, UDP 17, GRE 47, ESP 50, OSPF 89, VRRP 112 — plus a bulk mode that names a pasted list of numbers.Open
- Protocol Header Overhead & MTUHeader sizes for every common encapsulation, plus a stack builder that turns Ethernet, VLAN, PPPoE, MPLS, GRE, IPsec, VXLAN, Geneve and SRv6 into a total, an effective MTU and the TCP MSS for IPv4 and IPv6.Open
- Vendor CLI Cross-ReferenceTwenty operational tasks — BGP summary, MAC table, LLDP, port mirroring, packet capture, save and diff — with the command for IOS, IOS-XE, IOS-XR, NX-OS, EOS, VRP, Comware and Junos side by side.Open
3 tools
Datacenter & Cabling
PDU power and current, cooling load, cabling pinouts and optics compatibility.
- PDU Power & Breaker CalculatorTurn a rack load in watts into line current for single- or three-phase feeds, apply the 80 % continuous derating, pick the next standard breaker size and count the C13 and C19 receptacles the load needs.Open
- BTU & Cooling Load CalculatorA live converter between watts, kilowatts, BTU/hr, tons of refrigeration and kcal/h, plus CRAC sizing: enter the rack load, see the heat rejection and the recommended unit size with a stated redundancy factor.Open
- Cabling Pinout & Fiber Polarity ReferenceT568A and T568B side by side as tables and as color-coded strip diagrams, plus crossover and Cisco rollover wiring, PoE Mode A/B pin usage with the 802.3af/at/bt classes, MPO/MTP polarity A/B/C and the copper and fiber Ethernet standards.Open
1 tool
Credentials & Keys
Device password formats, hashes, certificates and SSH keys — all local.
1 tool
Config & Automation
Configuration diffing, template rendering, log filtering, line operations.
Writing
The reasoning behind the calculators
Longer pieces on the failures these tools exist to catch — worked through by hand, with the arithmetic shown, by the person who builds them.
- RoutingWhy a packet dies: three failures that look identical from the sourceNo route, no ARP reply, and two masks that disagree all produce the same symptom from the sending host. Here is how to tell them apart before you start changing configuration.21 October 2026 · 6 min read
- BGPWhat BGP summary-only actually hidesAn aggregate advertises address space, not the routes inside it. When the two do not match, summary-only turns a tidy configuration into a blackhole — and the routing table still looks correct.21 October 2026 · 5 min read
Nothing here needs an account, and the tools run without the network.
The whole toolkit is a static site with a service worker, so one visit is enough to make the tools work offline — on a laptop in a datacenter, on a phone with no signal. There is no NetKit server to be down and no upload of your input to be intercepted, because the tools have nothing to upload. The advertising script each page loads is the one third-party exception, and it is written down on the privacy page rather than implied away here.