Netfold

Netfold is a free, browser-based tool that consolidates IP addresses into the smallest possible set of CIDR blocks essentially an "IP supernetting" or summarization utility.

Here's what it does:

Core function: You give it a list of IP addresses and/or CIDR ranges (IPv4 or IPv6, mixed), and it "folds" them into the compactest, non-overlapping set of CIDR blocks that covers the same address space. This is useful for cleaning up firewall rules, access control lists, routing tables, or any situation where you want to reduce a long list of IPs into fewer, broader network blocks.

Input options: You can paste IPs directly into a text box (one per line, or comma/space-separated), or upload a .txt or .csv file. It handles plain IPs, CIDR notation, or a mix of both.

Output: Results are shown as a summary (how many CIDRs went in vs. how many come out), a sortable table with details like prefix length, IP version, and address type, and a plaintext list you can copy. There's also a CSV export option.

Privacy-focused: All processing happens entirely in the browser — no data is sent to any server.

It also has an Unfold mode, which does the reverse: expanding a CIDR block out into its individual constituent IPs or sub-ranges.

In short, it's a handy tool for network engineers and sysadmins who need to tidy up or optimize IP lists.