diff --git a/.gitignore b/.gitignore
index f3a8853..056489e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -22,4 +22,7 @@ node_modules
 *.swp
 *.pyo
 *.pyc
-*.env
\ No newline at end of file
+*.env
+
+# Claude Code config
+CLAUDE.md
\ No newline at end of file
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..db2ef06
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,104 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Nostr Market is an LNbits extension implementing NIP-15 (decentralized marketplace protocol) on Nostr. It enables merchants to create webshops (stalls) and sell products with Lightning Network payments, featuring encrypted customer-merchant communication via NIP-04.
+
+**Prerequisites:** Requires the LNbits [nostrclient](https://github.com/lnbits/nostrclient) extension to be installed and configured.
+
+## Common Commands
+
+All commands are in the Makefile:
+
+```bash
+make format      # Run prettier, black, and ruff formatters
+make check       # Run mypy, pyright, black check, ruff check, prettier check
+make test        # Run pytest with debug mode
+make all         # Run format and check
+```
+
+Individual tools:
+
+```bash
+make black       # Format Python files
+make ruff        # Check and fix Python linting
+make mypy        # Static type checking
+make pyright     # Python static type checker
+make prettier    # Format JS/HTML/CSS files
+```
+
+## Local Development Setup
+
+To run checks locally, install dependencies:
+
+```bash
+# Install Python autotools dependencies (needed for secp256k1)
+sudo apt-get install -y automake autoconf libtool
+
+# Install Python dependencies
+uv sync
+
+# Install Node dependencies (for prettier)
+npm install
+
+# Run all checks
+make check
+```
+
+## Architecture
+
+### Core Layers
+
+1. **API Layer** (`views_api.py`) - REST endpoints for merchants, stalls, products, zones, orders, direct messages
+2. **Business Logic** (`services.py`) - Order processing, Nostr event signing/publishing, message routing, invoice handling
+3. **Data Layer** (`crud.py`) - Async SQLite operations via LNbits db module
+4. **Models** (`models.py`) - Pydantic models for all entities
+
+### Nostr Integration (`nostr/`)
+
+- `nostr_client.py` - WebSocket client connecting to nostrclient extension for relay communication
+- `event.py` - Nostr event model, serialization, ID computation (SHA256), Schnorr signatures
+
+### Background Tasks (`__init__.py`, `tasks.py`)
+
+Three permanent async tasks:
+
+- `wait_for_paid_invoices()` - Lightning payment listener
+- `wait_for_nostr_events()` - Incoming Nostr message processor
+- `_subscribe_to_nostr_client()` - WebSocket connection manager
+
+### Frontend (`static/`, `templates/`)
+
+- Merchant dashboard: `templates/nostrmarket/index.html`
+- Customer marketplace: `templates/nostrmarket/market.html` with Vue.js/Quasar in `static/market/`
+- Use Quasar UI components when possible: https://quasar.dev/components
+
+### Key Data Models
+
+- **Merchant** - Shop owner with Nostr keypair, handles event signing and DM encryption
+- **Stall** - Individual shop with products and shipping zones (kind 30017)
+- **Product** - Items for sale with categories, images, quantity (kind 30018)
+- **Zone** - Shipping configuration by region
+- **Order** - Customer purchases with Lightning invoice tracking
+- **DirectMessage** - Encrypted chat (NIP-04)
+- **Customer** - Buyer profile with Nostr pubkey
+
+### Key Patterns
+
+- **Nostrable Interface** - Base class for models convertible to Nostr events (`to_nostr_event()`, `to_nostr_delete_event()`)
+- **Parameterized Replaceable Events** - Stalls (kind 30017) and Products (kind 30018) per NIP-33
+- **AES-256 Encryption** - Customer-merchant DMs use shared secret from ECDH
+- **JSON Meta Fields** - Complex data (zones, items, config) stored as JSON in database
+
+### Cryptography (`helpers.py`)
+
+- Schnorr signatures for Nostr events
+- NIP-04 encryption/decryption
+- Key derivation and bech32 encoding (npub/nsec)
+
+## Workflow
+
+- Always check GitHub Actions after pushing to verify CI passes
+- Run `make check` locally before pushing to catch issues early
diff --git a/static/components/shipping-zones.js b/static/components/shipping-zones.js
index 742021a..13f0357 100644
--- a/static/components/shipping-zones.js
+++ b/static/components/shipping-zones.js
@@ -19,7 +19,6 @@ window.app.component('shipping-zones', {
       currencies: [],
       shippingZoneOptions: [
         'Free (digital)',
-        'Flat rate',
         'Worldwide',
         'Europe',
         'Australia',
@@ -27,6 +26,7 @@ window.app.component('shipping-zones', {
         'Belgium',
         'Brazil',
         'Canada',
+        'China',
         'Denmark',
         'Finland',
         'France',
@@ -34,8 +34,8 @@ window.app.component('shipping-zones', {
         'Greece',
         'Hong Kong',
         'Hungary',
-        'Ireland',
         'Indonesia',
+        'Ireland',
         'Israel',
         'Italy',
         'Japan',
@@ -59,10 +59,9 @@ window.app.component('shipping-zones', {
         'Thailand',
         'Turkey',
         'Ukraine',
-        'United Kingdom**',
-        'United States***',
-        'Vietnam',
-        'China'
+        'United Kingdom',
+        'United States',
+        'Vietnam'
       ]
     }
   },
diff --git a/templates/nostrmarket/components/shipping-zones.html b/templates/nostrmarket/components/shipping-zones.html
index 3f0fd08..b0dbc34 100644
--- a/templates/nostrmarket/components/shipping-zones.html
+++ b/templates/nostrmarket/components/shipping-zones.html
@@ -48,26 +48,36 @@
           label="Countries"
           v-model="zoneDialog.data.countries"
         ></q-select>
-        <q-select
-          :disabled="!!zoneDialog.data.id"
-          :readonly="!!zoneDialog.data.id"
-          filled
-          dense
-          v-model="zoneDialog.data.currency"
-          type="text"
-          label="Unit"
-          :options="currencies"
-        ></q-select>
-        <q-input
-          filled
-          dense
-          :label="'Cost of Shipping (' + zoneDialog.data.currency + ') *'"
-          fill-mask="0"
-          reverse-fill-mask
-          :step="zoneDialog.data.currency != 'sat' ? '0.01' : '1'"
-          type="number"
-          v-model.trim="zoneDialog.data.cost"
-        ></q-input>
+        <div class="row items-start">
+          <div class="col q-mr-sm">
+            <q-input
+              filled
+              dense
+              label="Default shipping cost"
+              fill-mask="0"
+              reverse-fill-mask
+              :step="zoneDialog.data.currency != 'sat' ? '0.01' : '1'"
+              type="number"
+              v-model.trim="zoneDialog.data.cost"
+              :error="(zoneDialog.data.currency === 'sat' && zoneDialog.data.cost % 1 !== 0) || (zoneDialog.data.currency !== 'sat' && (zoneDialog.data.cost * 100) % 1 !== 0)"
+              :error-message="zoneDialog.data.currency === 'sat' ? 'Satoshis must be whole numbers' : 'Maximum 2 decimal places allowed'"
+              hint="Additional costs can be set per product"
+            ></q-input>
+          </div>
+          <div class="col-auto">
+            <q-select
+              :disabled="!!zoneDialog.data.id"
+              :readonly="!!zoneDialog.data.id"
+              filled
+              dense
+              v-model="zoneDialog.data.currency"
+              type="text"
+              label="Currency"
+              :options="currencies"
+              style="min-width: 100px"
+            ></q-select>
+          </div>
+        </div>
         <div class="row q-mt-lg">
           <div v-if="zoneDialog.data.id">
             <q-btn unelevated color="primary" type="submit">Update</q-btn>
@@ -83,7 +93,7 @@
             <q-btn
               unelevated
               color="primary"
-              :disable="!zoneDialog.data.countries || !zoneDialog.data.countries.length"
+              :disable="!zoneDialog.data.name || !zoneDialog.data.countries || !zoneDialog.data.countries.length || (zoneDialog.data.currency === 'sat' && zoneDialog.data.cost % 1 !== 0) || (zoneDialog.data.currency !== 'sat' && (zoneDialog.data.cost * 100) % 1 !== 0)"
               type="submit"
               >Create Shipping Zone</q-btn
             >