Subnet Calculator
Calculate IPv4 network, broadcast, and host ranges from CIDR.
OpenMerge, overlap-check, and diff IPv4 CIDR lists for security groups. - runs entirely in your browser. Free, fast and private.
Add one or two IPv4 CIDR sets to compare.
Merge adjacent ranges and highlight collisions.
See added and removed CIDRs for SG reviews.
Format results for AWS security group ingress.
CIDR Toolbelt is a free network & ops utility on OneDevToolkit. Merge, overlap-check, and diff IPv4 CIDR lists for security groups. It runs in your browser for this session - use the workspace on this page to try it.
Need a related step? Open the Network & Ops hub at /network-tools/ or the <a href="/blog/">blog</a> for longer workflows.
Processes data instantly with no server round-trips.
Your data never leaves your browser. Nothing is uploaded.
Works in any modern browser. Nothing to download or install.
No limits, no sign-up, no credit card required.
Works on desktop, tablet and mobile devices.
Beautiful in both themes. Your preference is saved.
Keyboard shortcut
Open CIDR Toolbelt when you need a quick result without uploading data to a third-party site.
No install required - bookmark the tool and return anytime.
Client-side processing keeps inputs on your device for core OneDevToolkit tools.
Answers for this tool. For site-wide help, open the FAQ hub.
CIDR Toolbelt merge, overlap-check, and diff ipv4 cidr lists for security groups. Output stays in your browser for quick iteration.
Prefer redacted samples. Even with local processing, treat prod credentials carefully and rotate anything accidentally shared.
No. Generators and linters produce text for you to copy into Git, CI, or consoles - they do not deploy for you.
Always run official CLIs (kubectl, terraform plan, actionlint, etc.) on the final files after using CIDR Toolbelt as a starting point.
Syntax may vary across Kubernetes/Terraform/GitHub Actions versions. Adjust generated snippets to your runtime version.
After the page loads, most authors work offline. Keep a local copy of critical manifests.
Use Sample to learn the format, edit, then Download/Copy into your editor.
Request it via Contact with the platform and version you use.