diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 00000000..86937fa4
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,75 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+XSLT Lab is an online XSLT editor and tester that uses Saxon for XSLT 2.0/3.0 transformations. The application consists of a React frontend and a Go backend that orchestrates Java/Saxon for XSLT processing.
+
+## Build Commands
+
+```bash
+# Full stack with Docker Compose (lightweight, no database)
+make compose-up
+make compose-down
+
+# Backend (Go)
+cd backend/src && go build -o ../server
+cd backend && ./server
+
+# Frontend (React/Vite)
+cd frontend && npm install
+VITE_BACKEND_URL=http://localhost:8000 npm run dev
+
+# Testing
+make backend-test        # Go tests: go test ./...
+make frontend-test       # npm tests: vitest
+
+# Docker images
+make backend-image
+make frontend-image
+```
+
+## Architecture
+
+### Frontend (`/frontend`)
+- React 18 + Vite SPA
+- **App.jsx** is the monolithic state container managing all workspace state, tabs, transformations
+- Monaco Editor for code editing (lazy-loaded)
+- LocalStorage persistence for workspace data (up to 3 workspaces)
+- `/lib/workspaceUtils.js` contains utility functions for parameter extraction, error parsing, XSLT manipulation
+
+### Backend (`/backend`)
+- Go/Gin HTTP server on port 8000
+- Executes Saxon via `java` command with generated args file
+- **POST /transform** - Main endpoint accepting `{xslt, version, parameters, trace}`
+- 10-second timeout per transformation
+- `/ext/` contains Java custom extension functions (uuid, date, base64, etc.)
+
+### Data Flow
+```
+Frontend (POST /transform) → Go Backend → java/Saxon → Parse trace/result → JSON response
+```
+
+### Pro Features (when VITE_GO_PRO=true)
+- Firebase authentication
+- PostgreSQL history storage
+- `/history` endpoint
+
+## Key Environment Variables
+
+**Frontend (build-time)**:
+- `VITE_BACKEND_URL` - Backend API endpoint
+- `VITE_GO_PRO` - Enable Pro features
+- `VITE_FIREBASE_CONFIG` - Firebase configuration
+
+**Backend**:
+- `DATABASE_URL` - PostgreSQL connection (Pro mode)
+- `SAXON_CLASSPATH` - Path to Saxon JARs (default in app.config)
+
+## Configuration Files
+
+- `/backend/app.config` - Backend port and Saxon classpath
+- `/docker-compose.local.yml` - Lightweight dev stack (no DB)
+- `/docker-compose.yml` - Full stack with PostgreSQL
+- `/charts/xslt-playground/` - Helm chart for Kubernetes deployment
diff --git a/frontend/index.html b/frontend/index.html
index bb5ec3e1..e7b7d0b8 100644
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -22,6 +22,30 @@
     <meta property="og:image" content="/logo.svg" />
     <link rel="canonical" href="https://xsltplayground.com/" />
     <link rel="icon" type="image/x-icon" href="/favicon.ico" />
+    <script type="application/ld+json">
+      {
+        "@context": "https://schema.org",
+        "@type": "WebApplication",
+        "name": "XSLT Playground",
+        "alternateName": "XSLT Lab",
+        "url": "https://xsltplayground.com/",
+        "description": "Free online XSLT editor, tester and optimizer. Transform XML documents with XSLT 1.0 and 2.0 stylesheets using Saxon processor.",
+        "applicationCategory": "DeveloperApplication",
+        "operatingSystem": "Any",
+        "offers": {
+          "@type": "Offer",
+          "price": "0",
+          "priceCurrency": "USD"
+        },
+        "featureList": [
+          "XSLT 1.0 and 2.0 support",
+          "Real-time XML transformation",
+          "Multiple workspaces",
+          "Variable tracing",
+          "Import/Export workspaces"
+        ]
+      }
+    </script>
     <style>
       body {
         margin: 0;
@@ -48,6 +72,7 @@
       .shell-title {
         font-weight: 700;
         font-size: 1.1rem;
+        margin: 0;
       }
       .shell-subtitle {
         font-size: 0.9rem;
@@ -109,7 +134,7 @@
         <div class="shell-top">
           <img src="/logo.svg" alt="XSLT Playground logo" class="shell-logo" />
           <div>
-            <div class="shell-title">XSLT Playground</div>
+            <h1 class="shell-title">XSLT Playground</h1>
             <div class="shell-subtitle">Loading the editor...</div>
           </div>
         </div>
diff --git a/frontend/src/App.jsx b/frontend/src/App.jsx
index 1eca12a3..15b9d0a5 100644
--- a/frontend/src/App.jsx
+++ b/frontend/src/App.jsx
@@ -1304,6 +1304,7 @@ export default function App() {
 
   return (
     <div className="app-container">
+      <h1 className="sr-only">XSLT Playground - Online XSLT Editor and Tester</h1>
       {ethicalAdsEnabled && (
         <div
           ref={ethicalSlotRef}
@@ -1894,6 +1895,7 @@ export default function App() {
         <div className="footer-left">
           <img src={logo} alt="XSLT Playground logo" className="logo" />
           <strong>xsltplayground.com</strong>
+          <span className="footer-tagline">Free XSLT Editor &amp; Tester</span>
           <a
             className="news-link"
             href={newsUrl}
diff --git a/frontend/src/style.css b/frontend/src/style.css
index 38673655..3474bf85 100644
--- a/frontend/src/style.css
+++ b/frontend/src/style.css
@@ -7,6 +7,18 @@ body,
   background: #f5f5f5;
 }
 
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border: 0;
+}
+
 a:focus-visible {
   outline: none;
   box-shadow: 0 0 0 2px rgba(74, 133, 255, 0.35);
@@ -867,6 +879,13 @@ a:focus-visible {
   flex-wrap: wrap;
 }
 
+.footer-tagline {
+  color: #536084;
+  font-size: 0.8rem;
+  padding-left: 0.5rem;
+  border-left: 1px solid #ccc;
+}
+
 .footer-theme-toggle {
   width: 32px;
   height: 32px;
@@ -1367,6 +1386,11 @@ a:focus-visible {
   color: #c7d2e3;
 }
 
+:root[data-theme="dark"] .footer-tagline {
+  color: #8a9ab8;
+  border-left-color: #3a4659;
+}
+
 :root[data-theme="dark"] .icon-button {
   color: #c7d2e3;
 }