The self-hosted toolbox for sysadmins and security work.
Subnets, certificates, DNS, mail records, Windows error codes and the rest of the daily lookups — in one container you run yourself. Nothing is logged, nothing is sent to a third party, and the tools that touch secrets never leave your browser.
Network
Addressing, name resolution and reachability
DNS lookup
Query A, AAAA, MX, TXT, NS, CNAME, SOA, CAA, SRV and PTR records against any resolver
server
RDAP and WHOIS lookup
Find who registered a domain or owns an IP range, with registration and expiry dates
server
Subnet calculator
Work out network, broadcast, usable range, mask and host count for any IPv4 or IPv6 block
server
Security
Certificates, hashes, tokens and hardening checks
Certificate / CSR decoder
Decode certificates and CSRs without contacting a server
in browser
Hash generator
Compute MD5, SHA-1, SHA-256, SHA-384 and SHA-512 digests and verify a checksum
in browser
HTTP security headers
Grade a site's response headers and see exactly which protections are missing
server
JWT decoder
Decode a JSON Web Token's header and claims without sending it anywhere
in browser
Password generator
Generate passwords or passphrases in your browser and see their real entropy
in browser
security.txt validator
Check a domain's security.txt for RFC 9116 fields, expiry and HTTPS delivery
server
TLS certificate checker
Check a certificate's expiry, names, issuer, key strength and negotiated protocol
server
Windows
Error codes, event IDs and Windows-specific lookups
Mail flow, deliverability and message headers
Encoding
Encoding, serialisation and text transforms
Ops
Capacity, scheduling, SLAs and unit maths