Browser-Based Network Utilities
Free Networking Tools for Every Task
IP lookups, DNS record checks, subnetting calculators, email authentication audits, and more — all browser-based, no installs or signups required.
IP Address Tools
What Is My IP Address?
Instantly find your public IPv4 address with geolocation details including city, region, country, and ISP.
→IP Address ↔ Binary Converter
Convert between dotted-decimal, binary, hexadecimal, and integer IP formats with class and scope detection.
→IPv4 to IPv6 Converter
Convert any IPv4 address to IPv6 — IPv4-mapped, 6to4 prefix, expanded hex, and per-octet notation.
Subnetting & IP Ranges
IPv4 Subnet Calculator
Calculate network address, broadcast address, usable host range, and subnet mask from any IP and CIDR prefix.
→CIDR to IP Range Converter
Expand any IPv4 CIDR block to its full range with subnet and wildcard masks, host counts, and address-type detection.
DNS & Domain Tools
DNS Record Checker
Query ten record types — A, AAAA, MX, TXT, CNAME, NS, SOA, CAA, SRV, and HTTPS — with DNSSEC status.
→DNS Propagation Checker
Compare a DNS record across Google and Cloudflare side by side to see whether a recent change has propagated.
→Reverse DNS Lookup
Find the hostname (PTR record) associated with any IPv4 address via in-addr.arpa resolution.
WHOIS Lookup
Query domain and IP registration details via modern RDAP — registrar, expiry dates, name servers, and abuse contacts.
Email Deliverability Tools
MX Lookup
Look up the MX records for any domain — every mail server, its priority, and the IPs they resolve to.
→TXT Record Lookup
Browse every TXT record on a domain — SPF, DMARC, verification tokens, and more — in one clean list.
→SPF, DKIM & DMARC Checker
Verify the email authentication TXT records on any domain in one click — SPF, DKIM, and DMARC together.
→SPF Record Lookup
Parse the SPF record for any domain with a live count against the SPF 10-DNS-lookup limit.
→SPF and DMARC Record Generator
Build copy-paste ready SPF and DMARC records from guided options with a built-in lookup-limit check.
→IP Blacklist Check
Check whether an IP address appears on Spamhaus, SpamCop, Barracuda, and other major DNS blacklists.
Security & Network Utilities
SSL Certificate Checker
Check the SSL/TLS certificate for any domain — issuer, expiry date, days remaining, and Subject Alternative Names.
→Common Port Number Reference
Searchable database of 86 TCP and UDP ports with category filters and exposure-risk flags on commonly attacked services.
→MAC Address Vendor Lookup
Enter any MAC address to identify the hardware manufacturer using the IEEE OUI database.
→Bandwidth Transfer Calculator
Estimate file transfer time at any speed — ideal and real-world results with protocol overhead, presets, and unit conversion.
Guides
The tools above answer a quick question; these guides explain the concepts behind them. They are written in plain language for students, IT pros, and anyone making sense of how networks actually work. The library covers DNS and domains, IP addressing and subnetting, MAC addresses, network ports, and firewalls. It also spans email authentication and deliverability, SSL/TLS certificates, the IPv4-to-IPv6 transition, and the OSI model. A step-by-step troubleshooting walkthrough ties the set together. More guides are on the way as the toolkit grows.
How to Find Your Public IP Address
What your public IP reveals, why it matters, and the fastest ways to find it on any device.
→ Deep DivePublic vs. Private IP Addresses
What separates public and private address space, NAT, and how traffic gets routed between them.
→IP Address Formats: Decimal, Binary, Hex, and How to Convert
Why IP addresses have multiple representations and how to move between them.
→ Deep DiveIPv4 vs. IPv6: What’s Changing and Why
Address exhaustion, dual-stack networking, and what the transition means for everyday infrastructure.
→Subnetting Made Simple: A Beginner’s Guide to CIDR
Learn CIDR notation, subnet masks, and how to divide networks — with worked examples.
→ Deep DiveVLSM and Supernetting: Beyond Basic Subnetting
Variable-length subnet masks, route aggregation, and when to use them in real network designs.
→What Is a MAC Address?
How MAC addresses work, where to find yours, and why vendor lookups are useful for network management.
→DNS Records Explained: A, AAAA, MX, CNAME, TXT, NS
A plain-English breakdown of every common DNS record type and when each one comes into play.
→ Deep DiveHow DNS Works: A Plain-English Walkthrough
The full DNS resolution chain from browser to authoritative nameserver, step by step.
→What Is Reverse DNS and When Do You Need It?
How PTR records work, why email deliverability depends on them, and how to check yours.
→How Long Does DNS Propagation Take?
Most changes go live in minutes, not 24 hours — what TTL really controls and why neighbors see updates first.
→How to Read a WHOIS Lookup (And Why It’s Now RDAP)
What registration data shows, why most fields are redacted, and how to read the status codes.
→ Deep DiveSPF, DKIM, and DMARC Explained: How They Work Together
How the three email-authentication records combine to keep your mail out of the spam folder.
→How to Set Up SPF and DMARC Without Breaking Email
A safe, monitoring-first rollout path that protects deliverability instead of blocking your own mail.
→What Is a DNS Blacklist? (And How to Get Off One)
How DNSBLs work, why a sending IP gets listed, and the steps to request removal.
→How SSL Certificates Work (And What to Do When They Expire)
The chain of trust, the 2026 shorter-validity limit, and the playbook for a cert that has expired.
→Common Network Ports: What They Are and What They Do
A practical overview of well-known ports, what services use them, and why they matter for security.
→ Deep DiveWhat Is a Firewall? Ports, Rules, and Traffic Filtering
How firewalls use port numbers and rules to control traffic, and how to read a rule set.
→ Deep DiveNetwork Basics: The OSI Model in Plain Language
All seven layers explained without the jargon, with real-world examples at each level.
→ Deep DiveHow to Troubleshoot Network Connectivity
A step-by-step diagnostic workflow using ping, traceroute, DNS checks, and the tools on this site.
Frequently Asked Questions
Are these network tools really free?
Yes. Every tool on this page is free to use with no signup, account, or download. The site is supported by ads, so the tools stay free for everyone.
Do these tools store my queries or data?
No. The tools run in your browser and send queries directly to public APIs like Google DNS-over-HTTPS. NetworkCheckr does not store your lookups, and nothing requires an account.
Do the tools work on mobile devices?
Yes. Every tool is browser-based and responsive, so it works on phones, tablets, and desktops. Nothing needs to be installed — any modern browser is enough.
Spot an error, run into a tool that isn’t working, or wish we had something we don’t? Drop us a line at hello@networkcheckr.com. Your feedback helps us make these tools better for everyone — thanks for taking the time.