Why this tool is useful
Use membership checks to review firewall samples, access-control fixtures or anonymized logs while keeping addresses in the current tab and making version mismatches explicit.
Developer & Data · runs locally
IPv4 and IPv6 CIDR Membership Checker
Test up to 1,000 IPv4 or IPv6 addresses against one same-version CIDR block and label every address inside or outside locally.
Ready. Your working data stays in this browser.
How it works
The CIDR and every candidate are parsed into unsigned 32-bit or 128-bit integers; a prefix-sized mask is applied and mixed IPv4/IPv6 comparisons are rejected.
Practical example
Against 192.0.2.0/24, 192.0.2.42 is inside and 192.0.3.1 is outside; the report preserves one result per submitted line.
Validation
The calculation is deterministic and explains validation errors instead of silently changing invalid input.
Privacy boundary
Input and output remain in this tab. Copy and download happen through browser APIs without a server upload.
Result passport
Every run reports its tool mode, timestamp and input/output size so transformed data can be audited.