Free DNS & Sysadmin Tools

Standalone utilities that don't need a full domain scan: build and validate records, generate keys, check propagation, and more. Everything below runs client-side or through this same no-account, no-tracking backend.

Last updated: August 29, 2026

Email & Domain Authentication

Build and validate the DNS records that make your outbound mail authenticate cleanly.

SPF Record Builder

Build a valid SPF record mechanism-by-mechanism, with a live RFC 7208 lookup-count meter so you catch a permerror before it ships.

📖 Guide

DKIM Key Pair Generator

Generates an RSA-2048 (or Ed25519, where your browser supports it) key pair locally. The private key never leaves your browser, formatted for a selector._domainkey TXT record.

📖 Guide

MTA-STS & TLS-RPT Generator

Generates the _mta-sts and _smtp._tls TXT records plus the mta-sts.txt policy file your enforcement mode needs.

📖 Guide

Global DNS Propagation Checker

Queries a record across a dozen independent public resolvers spread across the US and Europe to confirm a change has actually propagated.

📖 Guide

Network & Infrastructure Utilities

General-purpose networking calculators and connectivity checks.

IPv4 / IPv6 Subnet & CIDR Calculator

Network/broadcast address, netmask, wildcard mask, and usable host count from CIDR notation, for both IPv4 and IPv6.

📖 Guide

SSL/TLS Certificate Deep Inspector

Full chain validation, negotiated protocol/cipher, key strength, SAN coverage, and a downloadable expiry reminder.

📖 Guide

Port & Mail Server Connectivity Tester

Open/closed checks on 25, 465, 587, 143, 993, 110, 995, 21, 22, 80, 443 (plus a custom port) with banner and STARTTLS detection.

📖 Guide

Web & Server Security Diagnostics

Checks aimed at the web-facing side of your infrastructure, not just mail.

HTTP Security Headers Analyzer

Grades HSTS, CSP, X-Frame-Options, Referrer-Policy, Permissions-Policy and X-Content-Type-Options on any URL with an A-F score.

📖 Guide

Subdomain Takeover Checker

Scans common subdomain names for a dangling CNAME to a third-party platform (GitHub Pages, S3, Heroku, Netlify, Vercel and more) that could be silently hijacked.

📖 Guide

Cron Expression Builder & Explainer Coming soon

Converts crontab syntax to plain English and back, for scheduling backup/maintenance jobs.

Identity & System Administration

General sysadmin utilities that don't fit neatly under DNS, but come up constantly alongside it.

JWT Debugger & Decoder Coming soon

Decodes a JWT's header, payload and timestamps entirely in your browser. Nothing is sent anywhere.

Htpasswd & Password Entropy Generator Coming soon

High-entropy password generation with a bit-entropy readout, plus bcrypt/SHA-256 htpasswd hashing.

Guides

Plain-language reference for every DNS record type this site checks, how to set each one up, and how to troubleshoot it.

DNS & Email Record Guides

A full reference covering every record type on this site: what it does, how to set it up, and how to troubleshoot it. Nine guides, one per tool.