Network Tools
17 free toolsDNS, WHOIS, IP, subnet, and email deliverability lookups.
Network tools answer the questions behind a broken deployment or a suspicious domain: what does DNS say right now and from where, who registered a domain and when, what is my IP, how does a CIDR block expand, does this email address have a mail server. The lookups explain what the registry or resolver actually returned instead of summarizing it.
Lookups such as DNS, WHOIS, domain age, and MX checks go through our server to the registry or resolver; the address you query is not logged. Subnet and IP math run in your browser.
All 17 tools
Random Port Generator
Generate random TCP/UDP port numbers
IPv4 Subnet Calculator
Calculate network, broadcast, host range, and mask from CIDR
IP Range / CIDR Expander
Expand a CIDR block or IP range into every address
IPv6 Expander / Compressor
Expand or compress IPv6 addresses
MAC Address Generator
Generate random MAC addresses in any format
Well-Known Port Reference
Search common TCP and UDP port numbers
User-Agent Parser
Parse a User-Agent into browser, OS, and device
What Is My IP
See your public IP address, location, and connection details
DNS Lookup
Look up DNS records for any domain (A, MX, TXT, NS, and more)
DNS Propagation Checker
See if your DNS change has propagated — query multiple resolver networks at once and compare answers
SPF Record Checker & Generator
Check a domain's SPF record: syntax, the 10 DNS lookup limit with every include followed, and what each term means. Or generate one.
DMARC Record Checker & Generator
Look up a domain's DMARC record, grade the policy, explain every tag, verify external report addresses, and generate a correct record.
Email Validator
Check email syntax and whether the domain can receive mail (MX check)
Punycode Converter
Convert IDN domains to Punycode (xn--) and back, with homograph warnings
MAC Address Lookup
Look up the vendor behind any MAC address (IEEE OUI registry)
WHOIS Lookup
Look up domain registration and IP ownership via RDAP
Domain Age Checker
Check how old a domain is from its registration date
Guides
From the blog: the mechanisms, standards, and edge cases behind these tools.
- DMARC From p=none to p=reject: The Rollout That Doesn't Break Your Own Mail Publish p=none, read the aggregate reports, fix the usual failures and alignment, then step up to quarantine and reject without losing your own invoices. Oct 16, 2026 · uses DNS Lookup, DNS Propagation Checker, SPF Record Checker & Generator +2
- One IPv6 Address, Eight Ways to Write It The same 128 bits can be spelled at least eight legal ways, which is why string-comparing IPv6 addresses in logs, allowlists, and databases quietly fails. RFC 5952 picks exactly one canonical form — here are its four rules, worked through real output, plus the two places our expander deliberately departs from it. Aug 31, 2026 · uses IPv4 Subnet Calculator, IP Range / CIDR Expander, IPv6 Expander / Compressor +2
- WHOIS Is Effectively Dead. Here Is What RDAP Actually Returns Plain-text WHOIS on port 43 has been replaced by RDAP: JSON over HTTPS, standardized fields, and GDPR redaction. What changed, what you still get, and what every EPP status code actually means for your domain. Jul 27, 2026 · uses IPv4 Subnet Calculator, What Is My IP, DNS Lookup +2
- "Address Already in Use": Ephemeral Port Ranges, TIME_WAIT, and Picking a Dev Port EADDRINUSE has three different causes and most developers only know one: another process, a TIME_WAIT ghost from the server you just killed, or macOS AirPlay squatting on port 5000. Plus the ephemeral ranges Linux, Windows, and macOS actually use (none agree with IANA), demonstrated with real lsof, sysctl, and socket output. Sep 3, 2026 · uses Random Port Generator, IPv4 Subnet Calculator, Well-Known Port Reference +1
- DNS Record Types Explained: A, AAAA, CNAME, MX, TXT and the Rest What every DNS record type actually does, why you cannot put a CNAME at your root domain, how TTL really works, and how to read SPF, DKIM, DMARC, and CAA records. Jul 25, 2026 · uses What Is My IP, DNS Lookup, SPF Record Checker & Generator +1
- Domain Age: What RDAP Actually Tells You (and What It Can't) Domain age is one RDAP event: the current registration's creation date. Why some registries omit it, why re-registration resets it, and why Google doesn't rank on it. Sep 28, 2026 · uses DNS Lookup, WHOIS Lookup, Domain Age Checker
- Why MAC Address Vendor Lookup Fails on Modern Phones Every phone on your network since 2019 has been lying about its hardware address on purpose. How to read the U/L bit that gives a randomized MAC away, why some real addresses resolve to "IEEE Registration Authority", and what an OUI can and cannot tell you about a device. Aug 24, 2026 · uses MAC Address Generator, DNS Lookup, MAC Address Lookup
- DNS Propagation Is Not Real: What You Are Actually Waiting For Nothing "propagates" when you change a DNS record — millions of independent resolver caches just expire on their own schedules. Where the 24–48 hour folklore comes from, the TTL procedure that removes the wait, and why lookups made too early keep failing. Aug 19, 2026 · uses DNS Lookup, DNS Propagation Checker, WHOIS Lookup
- CIDR & Subnetting Explained: Reading /24, Masks, and Host Counts A no-memorization guide to CIDR notation and subnetting — what the slash number really means, how to count hosts in a /24 or /20, why the network and broadcast addresses are reserved, how subnet masks work in binary, and the quick mental math for everyday networking. Jun 26, 2026 · uses IPv4 Subnet Calculator, IP Range / CIDR Expander, IPv6 Expander / Compressor
- Email Normalization: Gmail Dots, Plus Tags, and the Rules That Only Apply to One Provider Why [email protected] and [email protected] are one inbox but [email protected] and [email protected] are two, what RFC 5321 says about case, and why stripping +tags for every domain quietly merges different people. Sep 18, 2026 · uses Email Validator, Punycode Converter
- Why Your URL Starts With xn--: Punycode Explained The xn-- prefix is not a broken link — it is the ASCII form DNS actually carries. How Punycode works, and why browsers show xn-- to block homograph attacks. Aug 29, 2026 · uses Punycode Converter, WHOIS Lookup
- A Valid Email Address Is Not a Deliverable One [email protected] passes every email regex ever written. So does a perfect address at a domain that refuses all mail, and one at a domain that does not exist. Syntax and deliverability are different layers — here is what each can and cannot catch, and where the honest limit is. Aug 20, 2026 · uses DNS Lookup, Email Validator