diff --git a/apps/mobile/.env.example b/apps/mobile/.env.example
new file mode 100644
index 00000000..cc493f58
--- /dev/null
+++ b/apps/mobile/.env.example
@@ -0,0 +1,19 @@
+# ─────────────────────────────────────────────────────────────
+# Vaultix Mobile – Environment Variables (Issue #557)
+# Copy this file to `.env` and adjust values for your setup.
+# ─────────────────────────────────────────────────────────────
+
+# The environment to run. One of: dev | testnet | production
+EXPO_PUBLIC_APP_ENV=dev
+
+# Backend API base URL (without trailing slash).
+# - dev:        your local NestJS backend
+# - testnet:    the staging API
+# - production: the live API
+EXPO_PUBLIC_API_URL=http://localhost:3000
+
+# Soroban RPC endpoint URL.
+# - dev:        local soroban-rpc (default port 8000, NOT 8545 which is EVM)
+# - testnet:    testnet Soroban RPC
+# - production: mainnet Soroban RPC
+EXPO_PUBLIC_RPC_URL=http://127.0.0.1:8000
diff --git a/apps/mobile/app/_layout.tsx b/apps/mobile/app/_layout.tsx
index 8ad9532b..e8381e0d 100644
--- a/apps/mobile/app/_layout.tsx
+++ b/apps/mobile/app/_layout.tsx
@@ -3,6 +3,7 @@ import { StatusBar } from 'expo-status-bar';
 import { SafeAreaProvider } from 'react-native-safe-area-context';
 import { ToastProvider } from '../components/Toast';
 import { hydrateSession } from '../services/session';
+import { validateEnv } from '../security/env';
 
 import { AppState, AppStateStatus } from 'react-native';
 import { useBiometricLock } from '../hooks/useBiometricLock';
@@ -11,6 +12,10 @@ import { MobileLockScreen } from '../components/MobileLockScreen';
 import { UpdatePromptModal } from '../components/UpdatePromptModal';
 import { useEffect, useRef, useState } from 'react';
 
+// #557 – validate environment configuration at app start.
+// Surfaces a visible console warning in development when config is missing.
+validateEnv();
+
 export default function RootLayout() {
   const { isEnabled, isUnlocked, authenticate, lock, disableBiometric } = useBiometricLock();
   const { needsUpdate, forceUpdate, latestVersion, updateUrl, isLoading } = useAppVersion();
diff --git a/apps/mobile/security/env.ts b/apps/mobile/security/env.ts
index ba0337c9..0a37e2ec 100644
--- a/apps/mobile/security/env.ts
+++ b/apps/mobile/security/env.ts
@@ -12,7 +12,8 @@ const configs: Record<Environment, EnvConfig> = {
   dev: {
     environment: 'dev',
     apiUrl: process.env.EXPO_PUBLIC_API_URL || 'http://localhost:3000',
-    rpcUrl: process.env.EXPO_PUBLIC_RPC_URL || 'http://127.0.0.1:8545',
+    // Soroban RPC runs on port 8000 (soroban-rpc standalone) — not 8545 (EVM).
+    rpcUrl: process.env.EXPO_PUBLIC_RPC_URL || 'http://127.0.0.1:8000',
   },
   testnet: {
     environment: 'testnet',
@@ -28,8 +29,42 @@ const configs: Record<Environment, EnvConfig> = {
 
 export const envConfig = configs[ENV];
 
+/**
+ * Validates that required environment variables are set.
+ * In development, surfaces a visible console warning when config is missing
+ * or still pointing at a localhost default (which may indicate the developer
+ * hasn't configured their local backend/rpc yet).
+ *
+ * Issue #557: Called at app start from app/_layout.tsx.
+ */
 export const validateEnv = () => {
-  if (!envConfig.apiUrl || !envConfig.rpcUrl) {
-    console.warn('Missing required environment variables for', ENV);
+  const warnings: string[] = [];
+
+  if (!envConfig.apiUrl) {
+    warnings.push('EXPO_PUBLIC_API_URL is not set');
+  }
+
+  if (!envConfig.rpcUrl) {
+    warnings.push('EXPO_PUBLIC_RPC_URL is not set');
+  }
+
+  if (ENV === 'dev') {
+    if (envConfig.apiUrl === 'http://localhost:3000') {
+      warnings.push(
+        'EXPO_PUBLIC_API_URL is using the default localhost URL — set it explicitly in .env if your backend runs elsewhere',
+      );
+    }
+    if (envConfig.rpcUrl === 'http://127.0.0.1:8000') {
+      warnings.push(
+        'EXPO_PUBLIC_RPC_URL is using the default local Soroban RPC URL — set it explicitly in .env if your RPC runs elsewhere',
+      );
+    }
+  }
+
+  if (warnings.length > 0) {
+    console.warn(
+      `[env] Environment configuration warnings for "${ENV}":\n` +
+        warnings.map((w) => `  • ${w}`).join('\n'),
+    );
   }
 };
diff --git a/apps/mobile/services/api.ts b/apps/mobile/services/api.ts
index 3fc90171..af95bac3 100644
--- a/apps/mobile/services/api.ts
+++ b/apps/mobile/services/api.ts
@@ -9,8 +9,10 @@ import {
 import { withRetry } from '../utils/retry';
 import { NotificationsResponse } from '../types/notification';
 import { getAccessToken, getSecureAccessToken } from './session';
+import { envConfig } from '../security/env';
 
-const API_BASE_URL = process.env.EXPO_PUBLIC_API_BASE_URL ?? 'http://localhost:3000';
+// Single source of truth: envConfig.apiUrl from security/env.ts (Issue #557)
+const API_BASE_URL = envConfig.apiUrl;
 
 /**
  * The Nest auth module is URI-versioned (`app.enableVersioning`), so its routes
diff --git a/docs/ENVIRONMENT.md b/docs/ENVIRONMENT.md
new file mode 100644
index 00000000..60db527b
--- /dev/null
+++ b/docs/ENVIRONMENT.md
@@ -0,0 +1,141 @@
+# Environment Variables
+
+This document lists every environment variable used across the Vaultix monorepo, grouped by owning service.
+
+> **Issue #579:** Configuration was previously scattered and undocumented. Contributors discovered required
+> variables by hitting runtime errors. This file is the single canonical reference.
+
+---
+
+## Conflict & Duplicate Register
+
+The following variables were identified as conflicting or duplicated. The **canonical** name is listed first.
+
+| Conflicting variable | Canonical variable | Service | Resolution |
+|---|---|---|---|
+| `EXPO_PUBLIC_API_BASE_URL` | `EXPO_PUBLIC_API_URL` | Mobile | **Removed** in #557 — `services/api.ts` now imports from `security/env.ts` |
+| `NEXT_PUBLIC_API_BASE_URL` | `NEXT_PUBLIC_API_URL` | Frontend | `escrow-api.ts` still reads `NEXT_PUBLIC_API_BASE_URL` for a URL-stripping helper; **should be migrated to `NEXT_PUBLIC_API_URL`** |
+| `API_BASE_URL` | `PORT` / `NEXT_PUBLIC_API_URL` | Backend (email config) | `API_BASE_URL` is used only to build an email verification link; consider migrating to `FRONTEND_URL` |
+
+---
+
+## Backend (`apps/backend`)
+
+| Variable | Required | Secret | Default | Purpose |
+|---|---|---|---|---|
+| `PORT` | No | No | `3000` | HTTP listen port for the NestJS API |
+| `NODE_ENV` | No | No | — | Runtime environment (`development`, `production`, `test`) |
+| `DATABASE_PATH` | No | No | `./data/vaultix.db` | SQLite database file path |
+| `JWT_SECRET` | **Yes** | **Yes** | — | Secret used to sign JWT auth tokens |
+| `STELLAR_NETWORK` | No | No | `testnet` | Stellar network (`testnet` or `mainnet`) |
+| `STELLAR_NETWORK_PASSPHRASE` | No | No | Derived from `STELLAR_NETWORK` | Stellar network passphrase |
+| `STELLAR_RPC_URL` | No | No | `https://soroban-testnet.stellar.org` | Soroban RPC endpoint |
+| `STELLAR_CONTRACT_ID` | **Yes** | No | — | Deployed escrow contract ID on Soroban |
+| `STELLAR_TIMEOUT` | No | No | `60000` | RPC call timeout in ms |
+| `STELLAR_MAX_RETRIES` | No | No | `3` | Max RPC retry attempts |
+| `STELLAR_RETRY_DELAY` | No | No | `1000` | Base retry delay in ms |
+| `HORIZON_URL` | No | No | Derived from `STELLAR_NETWORK` | Stellar Horizon server URL |
+| `WALLET_SECRET` | **Yes** | **Yes** | — | Secret key for the backend escrow wallet |
+| `CORS_ORIGINS` | No | No | — | Comma-separated list of allowed CORS origins |
+| `FRONTEND_URL` | No | No | `http://localhost:3001` | Frontend URL, used for WebSocket origin checks |
+| `API_BASE_URL` | No | No | `http://localhost:3000` | Backend URL, used for email verification link construction |
+| `REQUEST_LOG_SLOW_THRESHOLD_MS` | No | No | `5000` | Slow-request logging threshold in ms |
+| `IPFS_PROVIDER` | No | No | `pinata` | IPFS storage provider (`pinata` or `local`) |
+| `IPFS_GATEWAY_URL` | No | No | `https://gateway.pinata.cloud/ipfs/` | IPFS gateway URL |
+| `IPFS_LOCAL_NODE_URL` | No | No | `http://localhost:5001` | Local IPFS node URL |
+| `IPFS_MAX_RETRIES` | No | No | `1` | Max IPFS upload retries |
+| `PINATA_API_KEY` | No | **Yes** | — | Pinata API key |
+| `PINATA_SECRET_API_KEY` | No | **Yes** | — | Pinata secret API key |
+| `PINATA_JWT` | No | **Yes** | — | Pinata JWT token (alternative to API key + secret) |
+| `SMTP_HOST` | No | No | — | SMTP server host |
+| `SMTP_PORT` | No | No | `587` | SMTP server port |
+| `SMTP_USER` | No | **Yes** | — | SMTP username |
+| `SMTP_PASS` | No | **Yes** | — | SMTP password |
+| `EMAIL_FROM` | No | No | `no-reply@vaultix.local` | From address for outgoing emails |
+| `EMAIL_MAX_ATTEMPTS` | No | No | `5` | Max email send retry attempts |
+| `EMAIL_RETRY_BASE_DELAY_MS` | No | No | `60000` | Base delay for email retries in ms |
+| `EMAIL_VERIFICATION_BASE_URL` | No | No | `API_BASE_URL + /auth/profile/verify-email` | Base URL for email verification links |
+| `WEBHOOK_MAX_ATTEMPTS` | No | No | `6` | Max webhook delivery attempts |
+| `WEBHOOK_RETRY_SCHEDULE_MS` | No | No | — | Comma-separated retry delays in ms |
+| `WEBHOOK_REQUEST_TIMEOUT_MS` | No | No | `30000` | Webhook request timeout in ms |
+| `WEBHOOK_ALERT_FAILURE_RATE_THRESHOLD` | No | No | `25` | Failure rate % that triggers an alert |
+| `WEBHOOK_ALERT_MIN_DELIVERIES` | No | No | `10` | Min deliveries before alerting |
+| `WEBHOOK_ALERT_WINDOW_MINUTES` | No | No | `60` | Alert window in minutes |
+| `VITE_API_URL` | No | No | `http://localhost:3001` | Used by backend's test client (`src/clients/client.ts`) |
+
+---
+
+## Frontend (`apps/frontend` — Next.js)
+
+| Variable | Required | Secret | Default | Purpose |
+|---|---|---|---|---|
+| `NEXT_PUBLIC_API_URL` | **Yes** | No | `http://localhost:3000` | Backend API base URL |
+| `NEXT_PUBLIC_API_BASE_URL` | No | No | — | **Deprecated/conflicting** — used only in `escrow-api.ts` for URL stripping. Should be migrated to `NEXT_PUBLIC_API_URL`. |
+| `NEXT_PUBLIC_STELLAR_NETWORK` | No | No | `testnet` | Stellar network for wallet connections |
+| `NEXT_PUBLIC_WS_URL` | No | No | `http://localhost:3000` | WebSocket URL for real-time updates |
+| `CI` | No | No | — | Set by CI runners; controls Playwright retry behaviour |
+
+---
+
+## Mobile (`apps/mobile` — Expo / React Native)
+
+| Variable | Required | Secret | Default | Purpose |
+|---|---|---|---|---|
+| `EXPO_PUBLIC_APP_ENV` | No | No | `dev` | Environment selector (`dev`, `testnet`, `production`) |
+| `EXPO_PUBLIC_API_URL` | **Yes** | No | Per-env default | Backend API base URL (single source of truth in `security/env.ts`) |
+| `EXPO_PUBLIC_RPC_URL` | **Yes** | No | Per-env default | Soroban RPC endpoint URL |
+| `EXPO_PUBLIC_AUTH_PATH_PREFIX` | No | No | `/v1/auth` | Auth route prefix (Nest versioning) |
+| `EXPO_PUBLIC_WEB_BASE_URL` | No | No | `https://vaultix.app` | Web app base URL for share links |
+| `EXPO_PUBLIC_API_BASE_URL` | — | — | — | **Removed** in #557 — was conflicting with `EXPO_PUBLIC_API_URL` |
+
+---
+
+## Onchain Deployment (`apps/onchain`)
+
+No environment variables are read directly by the onchain deployment code. Contract addresses and network
+configuration are injected via the backend's `STELLAR_CONTRACT_ID`, `STELLAR_RPC_URL`, and `STELLAR_NETWORK`
+variables during deployment scripts.
+
+---
+
+## Cross-Service Variables (Must Agree)
+
+These variables must be consistent across services to avoid drift:
+
+| Variable group | Backend | Frontend | Mobile | Notes |
+|---|---|---|---|---|
+| **API URL** | `PORT` (listed on) | `NEXT_PUBLIC_API_URL` (points to) | `EXPO_PUBLIC_API_URL` (points to) | All three must resolve to the same backend instance |
+| **Stellar Network** | `STELLAR_NETWORK` | `NEXT_PUBLIC_STELLAR_NETWORK` | (derived from `EXPO_PUBLIC_APP_ENV`) | All services must target the same Stellar network |
+| **Soroban RPC** | `STELLAR_RPC_URL` | — | `EXPO_PUBLIC_RPC_URL` | Mobile and backend must use the same RPC endpoint |
+| **Contract ID** | `STELLAR_CONTRACT_ID` | — | — | Only backend needs this, but the deployed contract must match the network |
+
+---
+
+## Quick Start
+
+### Backend
+```bash
+# .env
+PORT=3000
+DATABASE_PATH=./data/vaultix.db
+JWT_SECRET=your-secret-here
+STELLAR_NETWORK=testnet
+STELLAR_CONTRACT_ID=your-contract-id
+WALLET_SECRET=your-wallet-secret
+```
+
+### Frontend
+```bash
+# .env.local
+NEXT_PUBLIC_API_URL=http://localhost:3000
+NEXT_PUBLIC_STELLAR_NETWORK=testnet
+NEXT_PUBLIC_WS_URL=http://localhost:3000
+```
+
+### Mobile
+```bash
+# .env
+EXPO_PUBLIC_APP_ENV=dev
+EXPO_PUBLIC_API_URL=http://localhost:3000
+EXPO_PUBLIC_RPC_URL=http://127.0.0.1:8000
+```