diff --git a/README.md b/README.md
index a2eeb08..525be48 100644
--- a/README.md
+++ b/README.md
@@ -72,6 +72,23 @@ The `CIDRCalculator` component accepts optional `defaultIp` and `defaultCidr` pr
 
 ---
 
+## Navigation Categories
+
+The site organises tools into three categories used consistently across the navbar dropdown, homepage filter tabs, and homepage section headings:
+
+| Category | Tools |
+|---|---|
+| Infrastructure & Config | Crontab to Systemd, Env to JSON, JSON to Env |
+| Security & DevSecOps | PII Masker & Log Scrubber, K8s Manifest Sanitizer |
+| Networking & Data | CIDR Subnet Calculator, CSV to JSON Schema Builder |
+
+These category labels are defined in two places:
+
+- `src/components/shared/Navbar.astro` — `toolCategories` array drives the desktop dropdown and mobile menu
+- `src/pages/index.astro` — filter tab labels and section `<h2>` headings
+
+---
+
 ## Project Structure
 
 ```