Network Diagnostic Tools
Free network lookup and diagnostic tools for DNS records, IP geolocation, reverse DNS, port checks, CIDR math, and user-agent parsing — no software to install.
Built for developers, by a developer.
All tools run locally in your browser. Your data never leaves your device.
In This Collection
DNS Lookup Tool
IP Address Lookup
MX Lookup
Open Port Checker
CIDR Calculator
Why this collection exists
Diagnose DNS misconfigurations, verify mail server records before a domain migration, resolve a hostname to its IP, or check whether a port is actually reachable — all directly in your browser, without installing dig, nslookup, or a network scanner. These tools cover the everyday lookups a developer, sysadmin, or support engineer runs while debugging domains, servers, and client connections.
Every lookup runs through public DNS-over-HTTPS resolvers or standard browser networking — nothing is logged server-side, and no account or install is required.
Best fit for
- Sysadmins verifying DNS propagation and MX records before a domain cutover
- Support engineers diagnosing why a customer can't reach a specific port or host
- Developers debugging CORS, redirect, or hosting issues by resolving hostnames to IPs
- Security-conscious users decoding a suspicious User-Agent string
- Network engineers calculating subnet ranges from CIDR notation
Featured tools in this collection
Start with the strongest tools in this workflow cluster.
DNS Lookup Tool
Query A, AAAA, MX, TXT, CNAME, NS, and SOA DNS records globally using Cloudflare DoH — for email, SSL, and domain debugging.
IP Address Lookup
Look up geolocation, ISP, ASN, and timezone data for any IPv4 or IPv6 address — with automatic detection of your current IP.
MX Lookup
Look up mail exchange records for a domain and inspect MX priorities, hosts, and TTL values.
Open Port Checker
Check whether a public TCP port is open, closed, or filtered on a hostname or IP address.
CIDR Calculator
Calculate subnet details from a CIDR notation — network address, broadcast, first/last host, usable hosts, subnet mask, and binary representation.
Website to IP Address
Resolve a website URL or domain to its public IPv4 and IPv6 address records.
Related categories
More tools like these, organized by category.
All tools in this collection
Browse the complete workflow cluster and jump into the tool you need next.
DNS Lookup Tool
Query A, AAAA, MX, TXT, CNAME, NS, and SOA DNS records globally using Cloudflare DoH — for email, SSL, and domain debugging.
IP Address Lookup
Look up geolocation, ISP, ASN, and timezone data for any IPv4 or IPv6 address — with automatic detection of your current IP.
MX Lookup
Look up mail exchange records for a domain and inspect MX priorities, hosts, and TTL values.
Nameserver Lookup
Check authoritative NS records for a domain and see which DNS provider serves the zone.
Hostname to IP
Find the IPv4 and IPv6 addresses behind a hostname using DNS A and AAAA records.
IP to Hostname
Run a reverse DNS lookup for an IPv4 or IPv6 address and find PTR hostnames.
Website to IP Address
Resolve a website URL or domain to its public IPv4 and IPv6 address records.
Open Port Checker
Check whether a public TCP port is open, closed, or filtered on a hostname or IP address.
CIDR Calculator
Calculate subnet details from a CIDR notation — network address, broadcast, first/last host, usable hosts, subnet mask, and binary representation.
User Agent Parser
Decode any User-Agent string — identify browser, engine, OS, device type, and bot classification.
Collection FAQ
Extra context around when to use this toolkit and where to start.
Do these tools actually query live DNS/network data, or simulate it?
They query real, live data — DNS Lookup and MX Lookup use Cloudflare's DNS-over-HTTPS resolver, IP/hostname tools resolve against live DNS, and Open Port Checker performs an actual TCP connection attempt to the target.
Can I look up any domain or only my own?
Any public domain or IP address. These are read-only diagnostic queries against public infrastructure — the same kind of information available via public DNS or `dig`.
Is my query history or the domains I look up stored anywhere?
No. Lookups are performed on demand and not logged or associated with your identity.
Related Collections
Move into adjacent workflows without losing context.