CertGrade: TLS & web-security scanner

Free TLS & web-security scanner.

Networking and security tools

Small, fast utilities for everyday network and security work. Every tool runs entirely in your browser: no input is sent to a server, no account, no tracking of what you type. They pair with the scanner, which grades any domain's TLS, headers and DNS posture.

Subnet calculator Free IPv4 and IPv6 subnet calculator: network address, broadcast, usable host range, netmask, wildcard mask, and subnet splitting. Runs in your browser. Password generator Generate strong random passwords and diceware passphrases locally in your browser using the EFF wordlist. Entropy shown in bits. Nothing is sent or stored. DNS lookup Look up A, AAAA, MX, TXT, NS, CAA, CNAME and SOA records from your browser over DNS-over-HTTPS via Cloudflare or Google. Dig-style raw view with TTLs. Cron expression builder Build cron expressions visually, or paste one to get a plain English explanation and the next run times in your timezone. Ranges, lists, steps and macros. MTU / MSS calculator Calculate TCP MSS from MTU for IPv4 and IPv6, with overhead presets for WireGuard, IPsec, GRE, PPPoE and VXLAN. Find the right MTU inside any tunnel. WireGuard config generator Generate WireGuard server and client configs with X25519 keypairs created locally in your browser. Private keys are never uploaded. QR code and .conf download.

Why client-side?

Tools that handle addresses, keys or passwords should not see your data at all. Everything on these pages is computed locally by your browser; you can verify it in devtools (no network requests carry your input). The one exception is the DNS lookup tool, which talks directly from your browser to the public Cloudflare or Google DNS-over-HTTPS resolver you select, never to this site's servers.