Network

URL Encoder/Decoder

Encode and decode URL

REST API Tester

Testing tool for REST API.

HTTP Status Code List

Complete list of HTTP status codes (1xx-5xx) with meanings, common causes, and fixes for developers. Includes a lookup tool — enter a code number to see details instantly.

curl Exit Code List: Look Up Any Code (1-99), Meaning & Fix

Search the full list of curl exit codes (1-99) by number — see what each one means, common causes, and the exact fix. A developer reference for CI/CD, cron jobs, and shell scripts.

curl Command Generator

Specify the HTTP method, URL, headers, body, and authentication method in the form to generate a ready-to-run curl command you can copy and paste. No request is actually sent, so CORS restrictions never apply.

Subnet Calculator & Quick-Reference Table — Free, /1–/32 CIDR

Instantly calculate the network address, broadcast address, and usable host count from an IPv4 address and subnet mask. Includes a full /1–/32 subnet mask quick-reference table for network design and troubleshooting — fr...

CIDR / Subnet Mask Reference Table

A reference table of subnet masks, wildcard masks, and usable host counts for every prefix length from /0 to /32. Enter how many hosts you need and the smallest CIDR block that fits is highlighted automatically.

What Is My IP Address? Free IP Checker

Instantly check your current global IP address for free. Also shows HTTP connection details and browser environment info — handy for verifying your VPN exit node or device settings.

IP WHOIS Lookup

Look up WHOIS information for any IP address using the RDAP protocol. View the owning organization, network range, country, registration dates, and abuse contact.

IP Address / Domain Blacklist (DNSBL) Checker

Enter an IP address or domain to check it against major DNSBLs (blacklists) such as Spamhaus, SORBS, Barracuda, and SpamCop all at once to see if it's been flagged as a spam source.

IP Range ⇔ CIDR Converter

Enter a start and end IP to split that range into the smallest possible set of CIDR blocks, or enter CIDR notation (e.g. 192.168.1.0/24) to get the block's first/last IP and total address count. Useful for firewall and A...

IP Address Validator — Check IPv4/IPv6 Format & Detect Private Ranges (Free)

Instantly check whether a string is a valid IPv4 or IPv6 address and automatically classify it as private, loopback, link-local, multicast, or public. Runs entirely in your browser — no external lookups, pure format vali...

IPv6 CIDR Reference Table — Address Counts by Prefix Length (Free)

A reference table showing the number of addresses and equivalent /64 subnets for every IPv6 prefix length from /0 to /128. Enter how many /64 subnets you need and the best-fitting prefix length is highlighted automatical...

Subnet Overlap Checker — Detect Whether Two CIDR Blocks Overlap (Free)

Enter two IPv4 CIDR blocks (e.g. 192.168.1.0/24) and instantly find out whether they are identical, one contains the other, or they don't overlap at all. Useful for catching conflicts when designing firewall rules or VPC...

Domain WHOIS Lookup (Free)

Free WHOIS/RDAP lookup for any domain. Check the registrar, registrant, registration date, expiry date, and name servers instantly in your browser.

Punycode Converter (Internationalized Domain Names)

Convert internationalized domain names (IDN) containing non-ASCII characters, such as Japanese, to and from Punycode (an ASCII-compatible encoding).

Domain Name Validator (RFC Compliance Check)

Check whether a domain name complies with the RFC 1035/1123 syntax rules. Validates label length, total length, allowed characters, and hyphen placement individually, showing the specific reason for any violation.

SSL Certificate Checker (Expiry & Issuer Lookup)

Enter a domain name to check its SSL/TLS certificate's expiry date, issuer, SAN, and fingerprint. Days remaining are color-coded so you never miss a renewal and risk site downtime.

TLS Protocol Version Diagnostic Tool

Enter a domain name to check which TLS versions (1.0-1.3) it supports. Instantly see whether deprecated legacy versions are still enabled on your server, for free.

Free Internet Speed (bps) Converter | Kbps, Mbps, Gbps & Bandwidth Guide

Free tool: enter a connection speed in bps, Kbps, Mbps, or Gbps and instantly convert it to every unit at once. Understand the difference between bit and byte units (÷8), plus bandwidth needed for streaming, gaming, and...

Port Number Reference

A reference list of common TCP/UDP port numbers and what uses them — FTP, SSH, HTTP, HTTPS, MySQL, Redis, and more. Useful for configuring firewall rules and troubleshooting "connection refused" errors, with a live searc...

Email Address Validator

Instantly check whether an email address matches a practical RFC 5322-style format, and verify whether its domain can actually receive mail (MX record lookup). Free tool for form validation and mailing list cleanup.

SPF/DKIM/DMARC Record Checker

Look up SPF, DMARC, and DKIM records for any domain in real time and diagnose your anti-spoofing email authentication setup.

DNS Record Type Reference Guide

A reference covering the DNS record types you need for running mail and websites — A, MX, TXT, SPF, DKIM, DMARC and more — with purpose, syntax examples, and gotchas for each.

DNS Propagation Checker (Free) - Check DNS Records Worldwide

Free tool to query a domain's DNS records against multiple public resolvers around the world (Google, Cloudflare, and more) at once, so you can instantly see whether a nameserver or record change has propagated globally.

DNSSEC Checker

Query a domain's DNSKEY record against multiple public DNS resolvers (Google, Cloudflare, and more) to check whether its DNSSEC signature chain validates correctly.

MTA-STS Policy Checker

Fetches a domain's _mta-sts TXT record and mta-sts.txt policy file to diagnose whether MTA-STS (mandatory TLS encryption for inbound mail) is configured correctly.

DANE/TLSA Record Checker

Query the TLSA records published by a domain's mail servers (MX hosts) against multiple public DNS resolvers to check whether DANE certificate pinning is configured.

TLS-RPT (SMTP TLS Reporting) Record Checker

Fetches a domain's _smtp._tls TXT record to diagnose whether the report destination (rua) for failed TLS connections is configured correctly per RFC 8460. Useful alongside MTA-STS/DANE.

DMARC Aggregate Report Viewer

Upload a DMARC aggregate report (XML, gzip, or ZIP) from your mail server to see SPF/DKIM authentication and policy results by source IP in a readable table. Parsing happens 100% in your browser — the file is never uploa...

DKIM DNS Record Generator

Enter a selector name and public key (PEM format) to generate the DNS TXT record for DKIM signing (v=DKIM1; k=rsa; p=...). Public keys longer than 255 characters are automatically split into BIND zone file format.

Email Header Analyzer

Paste the raw headers of a received email (Received:, Authentication-Results:, etc.) to see the delivery path broken down hop by hop, along with SPF/DKIM/DMARC results. Parsing runs 100% in your browser.