# Subnet Highlighter

> Automatically highlights CIDR subnet masks on any page and shows IP count on hover

Canonical page: [https://chrome-stats.com/d/subnet-highlighter](https://chrome-stats.com/d/subnet-highlighter)

## Overview

- **ID:** `subnet-highlighter`
- **Platform:** Firefox
- **Type:** Firefox add-on
- **Status:** Available
- **Publisher:** Link
- **Category:** web-development,privacy-security
- **Daily users:** 3
- **Version:** 1.9
- **Last updated:** 2026-08-31
- **First published:** 2026-08-21
- **Size:** 19 KB
- **Data as of:** 2026-09-26
- **Store listing:** [Firefox Add-ons Store](https://addons.mozilla.org/firefox/addon/subnet-highlighter/)

## Description

Subnet Highlighter automatically scans every page and highlights all CIDR subnet masks — both IPv4 (/0–/32) and IPv6 (/0–/128). Hover over any highlighted mask to instantly see detailed network information.

<strong>IPv4 shows:</strong>
- Network &amp; broadcast address, first/last host
- Total IPs, usable hosts, subnet mask, wildcard
- Binary mask representation
- Class (A/B/C), Private/Public (RFC1918)
- Parent network, host offset, reverse DNS zone (PTR)
- Subnets if split into /28, /29, /30

<strong>IPv6 shows:</strong>
- Network address, first/last host
- Total addresses (as power of 2)
- Type: Global Unicast, Link-local, ULA, Multicast, Loopback
- Parent network, reverse DNS zone (ip6.arpa)
- Subnets if split

IPv4 masks are highlighted in yellow, IPv6 in blue. Works on any page including wikis, monitoring dashboards, NOC tools, and RIPE/BGP looking glasses.

## Rankings

- #56,427 — Overall
- #120 — highlighter
- #171 — submit

## Permissions and access

### Permissions

- `activeTab`

### Content script matches

- `<all_urls>`

## Safety

- **Risk impact:** Moderate risk impact
- **Risk likelihood:** High risk likelihood

### Analysis details

- Allows access to all websites, posing a significant security risk as it can monitor and modify data from any visited site.
- This extension was recently updated in the past month. New updates may not be stable or safe.

> Some risk analysis details are omitted from this free response. [Upgrade to view the full analysis](https://chrome-stats.com/pricing).

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- [Flex Subnetting](https://chrome-stats.com/d/flex-subnetting) — 2 users
- [CIDR Calculator](https://chrome-stats.com/d/cidr-calculator)
- [IPvFooBarBaz](https://chrome-stats.com/d/ipvfoobarbaz) — 235 users, 4.67 / 5
- [IPvFoo](https://chrome-stats.com/d/ipvfoo) — 7,436 users, 4.79 / 5
- [IP Address Viewer](https://chrome-stats.com/d/yenrehipaddressviewer) — 1 users
- [IPvFooBar](https://chrome-stats.com/d/ipvfoobar) — 257 users, 4.83 / 5

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Source: [Chrome-Stats](https://chrome-stats.com/d/subnet-highlighter)