Free Networking and Internet Tools
Free networking tools that run in your browser: subnet and CIDR calculators, an internet speed converter, a download time calculator and a port reference.
Seven free tools for network engineers, home-lab builders and anyone who has ever stared at a router wondering why the download is slow. Every calculator runs in your browser, needs no sign-up, and tells you which units it is using rather than leaving you to guess.
Quick answer
If you only need one thing: the Subnet Calculator works out any IPv4 or IPv6 subnet, the Internet Speed Converter explains why 100 Mbps is 12.5 MB/s, and the Common Port Numbers reference tells you what is listening on a port and whether it should be exposed. All seven are free and nothing you type leaves your device.
IP addresses and subnetting
IPv4 and IPv6
Subnet Calculator: IPv4, IPv6, VLSM and Wildcard
Work out a subnet from an IP address and a prefix, split it with VLSM, and read the mask, wildcard and binary view.
- IPv4 and IPv6 network, broadcast and usable range
- VLSM splitting with wasted-address count
- Wildcard mask, binary view and copy-to-clipboard
CIDR
CIDR to IP Range Converter
Turn CIDR notation into an address range and back, including the exact set of CIDR blocks that covers any range.
- Network, broadcast, mask, wildcard and usable hosts
- Any IPv4 range summarised as aligned CIDR blocks
- IPv6 CIDR blocks with address count
IP lookup
Who Is My ISP? Check Your Provider, IP and ASN
See your public IP address, the provider behind it, the ASN, the reverse-DNS hostname and an approximate location.
- Your connection, or any IP you type
- Provider, organisation, ASN and hostname
- Explains why the ISP name can look wrong
Internet speed and transfer time
Speed units
Internet Speed Converter and Bandwidth Calculator
Convert between Mbps, MB/s, Kbps and Gbps, then calculate how much speed a household actually needs.
- Every common speed unit, decimal and binary
- Mbps to MB/s explained in plain language
- Bandwidth needs from your devices and activities
Transfer time
Download Time Calculator
Enter a file size and a connection speed to see how long a download or upload will take.
- Transfer time from file size and speed
- The same file compared across common connections
- Optional protocol overhead allowance
Reference and writing
Reference
Common Port Numbers Reference
Searchable reference of the common TCP and UDP ports: what each service does and which should never be public.
- More than 70 ports with plain descriptions
- Encrypted and risky ports flagged
- Search by number, service or description
Writing
Word Counter with Readability and Keyword Analysis
Count words, characters and sentences as you type, with readability scores, reading time and keyword density.
- Grapheme-correct counting for emoji and CJK
- Four readability scores plus reading and speaking time
- Keyword density and repeated phrase analysis
How these tools work, and what happens to your data
- Every calculator is a single page that runs its own JavaScript in your browser. There is no server-side processing.
- Nothing you type into a calculator is uploaded, logged or stored. Refresh the page and it is gone.
- The Who Is My ISP tool is the one exception: to resolve an address it must send that address to a public IP-geolocation API, which is how any such lookup works.
- Each page states the units it uses and the standard it follows, and links to the primary source, so you can check the maths yourself.
Cite this collection
Afroz Ahmad, “Free Networking and Internet Tools”, afrozahmad.com. 28 September 2026. Available at https://afrozahmad.com/tools/
Suggested citation: Afroz Ahmad, Free Networking and Internet Tools (afrozahmad.com), reviewed 28 September 2026.
These tools were reviewed and fact-checked on 28 September 2026.
About this tool. It was built and is maintained by Afroz Ahmad, a CCIE with more than 20 years in networking, and it was reviewed against its listed sources on 28 September 2026. Where this page and an official source disagree, the official source wins.
Are these networking tools really free?
Yes. Every tool on this page is free, needs no account and no sign-up, and runs entirely in your browser. There is nothing to install and no usage limit.
Do the tools store or upload what I type?
No. The calculations run in JavaScript on your own device. IP addresses, file sizes and text you type are not sent to this site, and nothing is saved. The only exception is the Who Is My ISP tool, which has to ask a public API for the details of an IP address in order to look it up.
Which tool should I use for subnetting?
Use the Subnet Calculator when you know the address and prefix and want the network details plus VLSM splitting. Use the CIDR to IP Range Converter when you need to turn notation into a first and last address, or turn an address range back into CIDR blocks.
Can I embed or cite these tools?
Yes. Each tool page carries a citation line you can copy, and you are welcome to link to any tool or embed it. Citation and attribution details are on each tool page.
Do the tools work offline?
The calculators do, because the logic runs in your browser and needs no server. A page has to load once while you are online, and the ISP lookup always needs a network connection because it queries a public IP database.
Why are the numbers different from another calculator?
Usually a units mismatch. File sizes can be decimal (MB, 1,000,000 bytes) or binary (MiB, 1,048,576 bytes), and speeds are in bits per second while file sizes are in bytes. Each tool here states which unit it is using and lets you switch, which is why the same file can appear to take longer on one site than another.
Primary sources behind these tools
- IANA Service Name and Transport Protocol Port Number Registry – the authority for port assignments, and the source behind the port reference.
- RFC 6335 – the policy for assigning and registering port numbers, including the three ranges the port tool describes.
- RFC 4632 – classless inter-domain routing, the definition behind the subnet and CIDR calculators.
- NIST SI prefixes – the decimal prefix definitions used by the speed and file-size conversions.