Two ways to describe the same set of addresses

CIDR notation and a start-end range describe overlapping but not identical things. A CIDR block is always a power-of-two-sized, alignment-constrained chunk of address space — 192.168.1.0/28 has to start at a multiple of 16, because the block boundary is defined by the prefix length, not by whatever address you feel like starting from. A plain range (10.0.0.5-10.0.0.19) has no such constraint — it can start and end anywhere, at the cost of not being expressible as a single routing prefix. This tool accepts either because both show up constantly in practice: CIDR blocks from network design, arbitrary ranges from vendor documentation or firewall rule exports.

Why there's a cap on address count

Expanding a /8 would mean generating and rendering over 16 million lines of text in the browser tab, which would freeze the page rather than produce something useful. The cap exists to keep the tool responsive for its actual use case — small allowlists, DHCP scopes, subnet audits — rather than pretending to support address-space-scale enumeration a browser was never going to handle well anyway.