# Plan your IP space, visually

> Subnet Planner is an install-free, file-based IPAM-lite: enter a parent block and the subnet sizes you need and it lays out an optimal VLSM allocation, draws a visual map of allocated / reserved / free space, flags overlaps, and finds the next free block of any size. Name each subnet with VLAN / site / status; the plan persists locally and exports as JSON or CSV. It also does CIDR math and IPv6 expand/compress. Everything runs in your browser — no NetBox install, no account, nothing uploaded.

Live tool: https://lofttools.com/tools/dev-tools/subnet-planner

Category: Dev Tools


## What it does

- VLSM planner: give a parent block + the subnet sizes you need, get an optimal leaf→root allocation
- Visual address-space map (SVG): see allocated, reserved and free space at a glance, colored by status
- Allocation tracker: name each subnet and tag it with VLAN, site, purpose and status — the plan persists
- Overlap / conflict detection across the whole plan (the thing spreadsheets get wrong)
- Free-space finder: 'find the next free /27 in 10.0.0.0/8'
- CIDR calculator: network, broadcast, usable range, host count, mask ⇄ wildcard
- CIDR aggregation / supernetting and IPv6 expand / compress
- Import / export the plan as JSON or CSV — round-trips with the spreadsheets you already use
- Runs entirely in your browser — the plan is a file you own, nothing is uploaded

## How it works

1. **Set the parent block** — Enter the block you're planning (e.g. 10.0.0.0/16). The visual map shows the whole space.
2. **Allocate subnets** — List the subnet sizes you need for a VLSM split, or add named subnets manually with VLAN / site / status.
3. **Check + export** — The plan flags overlaps and finds free space; export it as JSON or CSV — it's a file you own.

## FAQ

### Is my network plan uploaded anywhere?

No. Everything is computed in your browser and the plan is stored locally and exported as a file you keep. Network designs are sensitive (internal topology), so nothing is sent to a server — open DevTools' Network tab and you'll see no data leave.

### How is this different from a subnet calculator?

A calculator does one calculation and forgets it. This is a planner: it lays out a full VLSM allocation, keeps a persistent named plan (VLAN/site/status per subnet), detects overlaps across the whole plan, finds free space, and visualizes the address space — then exports the plan as a file.

### How is it different from NetBox or phpIPAM?

NetBox and phpIPAM are excellent but heavyweight — a server, a database, and an account. This is the instant, private, file-based middle ground for when you just need to design and record an allocation. It even exports CSV that those tools can ingest, so it's a feeder, not a walled garden.

### Does it do IPv6?

It does IPv6 expand/compress and CIDR math, plus IPv4 VLSM, aggregation, and the visual map. Full IPv6 nibble-boundary subnetting and ULA generation are on the roadmap; IPv4 planning is complete today.

### Can it discover what's actually on my network?

No — a browser can't ping-sweep, ARP-scan, or query SNMP. This is the design and record-of-truth layer; live discovery is NetBox/nmap territory. Import (CSV/JSON) is how the current reality gets into your plan.

## Tips

- **Plan with VLSM, not guesswork** — Enter your parent block and the host counts you need per subnet — the planner carves an optimal, non-overlapping allocation.
- **Find free space fast** — Ask for the next free /27 (or any size) in a block and the planner returns the first available aligned range.
- **Your plan is a file** — Export to JSON or CSV and commit it to git, attach it to a ticket, or email it. Import to pick up where you left off.

## Subnet Planner vs. the alternatives

|  | Loft Subnet Planner | NetBox / phpIPAM | Calculator sites |
| --- | --- | --- | --- |
| Install / server / account | None | Server + DB | None |
| Persistent plan | Yes (a file you own) | Yes (in the DB) | No |
| VLSM + visual map | Yes | Yes (heavy) | Single calc |
| Overlap detection | Yes | Yes | No |
| Runs locally / private | Yes | Self-host | Ad-laden |
| Cost | Free | Free (ops cost) | Free/ads |

_A planner and record-of-truth, not a live discovery tool — no ping sweep, ARP scan, or SNMP (a browser can't). Import is how reality gets in; for live discovery and large-team IPAM, NetBox/nmap are the right tools._

## Privacy — what we do not do

This tool runs entirely in the browser via WebAssembly. Your file never reaches a Loft Tools server. Specifically:

- **No upload.** The file bytes load into the browser tab's memory and process on your own CPU. Open DevTools → Network and observe zero outbound requests carrying file data while Plan your IP space, visually runs.
- **No AI training on your file.** Loft does not train models. We could not train on a file we cannot see.
- **No content scanning.** No virus, copyright, or content-moderation pass against your file. The bytes are not accessible to us.
- **No server-side log of file contents, filenames, or EXIF metadata.** Cloudflare edge captures URL and truncated IP for abuse defense (standard CDN behaviour). Cloudflare Web Analytics records anonymous page hits, no cookies, no PII. Nothing about your file content reaches any log.
- **No retention.** Close the tab and the file leaves browser memory. No backups exist on our side because no copy ever existed on our side.
- **No account.** No email, no signup, no auth, no telemetry tied to you.
- **Offline-capable after first visit** (PWA). Once you've loaded a tool, it caches; later sessions work without internet. For high-sensitivity files, run the tool once online to warm the cache, then disconnect before processing.

Compare with upload-based services: each transmits your file to a processing server. Even over HTTPS, each has logs, retention windows, and subpoena exposure. Loft has none of these because the server architecture does not include your file.

## More

- All tools: https://lofttools.com/tools
- Category: https://lofttools.com/tools/dev-tools
- LLM index: https://lofttools.com/llms.txt