Subnets Preview

Preview IP subnet layouts inside VS Code / Cursor using the Visual Subnet Calculator — without leaving the editor.

Export JSON from v0-subnets (or any compatible networkAddress + subnets[] file), run Subnet: Preview JSON, and the layout opens in Simple Browser with Divide/Join, notes, and colors.

Features

In-editor preview — opens Simple Browser beside your code (no external browser required).
Works without a JSON file focused — finds docs/subnet-config-*.json (or your configured glob) automatically.
Smart file pick — uses the focused editor only when it contains valid v0-subnets JSON; ignores unrelated JSON (e.g. tasks.json).
Empty calculator fallback — if no config exists in the workspace, opens a blank v0-subnets page to start planning.
No telemetry — no analytics, no background network calls from the extension itself.
Workspace-local reads only — no shell, no Python, no access to secrets or env files.

Usage

Install the extension.
Open a workspace that contains a v0-subnets JSON export (optional).
Run Subnet: Preview JSON from the Command Palette (Cmd+Shift+P / Ctrl+Shift+P).

Or bind a keyboard shortcut to command network.subnetPreview.open.

Which config file is used?

Situation	File used
Focused editor has valid v0-subnets JSON	That file
No valid JSON focused	Latest match of `network.subnetPreview.configGlob` (default: `docs/subnet-config-*.json`)
Primary glob finds nothing	Tries `network.subnetPreview.configFallbackGlobs` (default: `*/subnet-config*.json`)
Multiple matches	Latest path (sorted); set `promptWhenMultiple` to `true` for a picker
No config in workspace	Empty v0-subnets calculator (if `openEmptyWhenMissing` is `true`)

Re-run the command after saving JSON changes — an already-open Simple Browser tab does not auto-refresh.

JSON format

Compatible with exports from v0-subnets.vercel.app:

{
  "networkAddress": "10.0.0.0",
  "maskBits": "16",
  "subnets": [
    {
      "networkAddress": "10.0.0.0",
      "maskBits": 24,
      "note": "app-uat",
      "color": "blue"
    }
  ]
}

Settings

Setting	Default	Description
`network.subnetPreview.configGlob`	`docs/subnet-config-*.json`	Primary workspace glob
`network.subnetPreview.configFallbackGlobs`	`["*/subnet-config*.json"]`	Extra globs if primary finds nothing
`network.subnetPreview.promptWhenMultiple`	`false`	Show picker when multiple configs match
`network.subnetPreview.openEmptyWhenMissing`	`true`	Open empty calculator when no config file exists

Privacy and data handling

Data	Handled how
Telemetry	None.
Workspace JSON	Read locally via VS Code API only.
Preview URL	Built in-process; opens `https://v0-subnets.vercel.app/?config=<base64>`.
Third party	v0-subnets receives your layout (CIDRs, notes) in the URL query when the page loads. Avoid personal data in `note` fields.
PII	Extension does not collect or store PII.

Security

Config paths must stay inside the workspace folder.
JSON is validated (v0-subnets shape) and size-capped (1 MiB).
Preview URL host is fixed to v0-subnets.vercel.app only.
Error toasts are generic (no filesystem paths).

Requirements

VS Code 1.80+ or Cursor with Simple Browser support.
A workspace folder open (not a single loose file).

Publisher

newbmiao · Extension ID newbmiao.subnets-preview

License

MIT