diff --git a/apps/web/app/api/projects/route.ts b/apps/web/app/api/projects/route.ts
index 3206b5d..bd9f7a9 100644
--- a/apps/web/app/api/projects/route.ts
+++ b/apps/web/app/api/projects/route.ts
@@ -1,4 +1,5 @@
 import { FREE_TIER_LIMIT, PRO_TIER_LIMIT } from "@/lib/constants"
+import { ensureMetronomeCustomer, ingestUsageEvent } from "@/lib/metronome"
 import {
   createAuthServerClient,
   createProject,
@@ -87,6 +88,9 @@ export async function POST(request: NextRequest) {
       return NextResponse.json({ error: "User email not found" }, { status: 400 })
     }
 
+    // Ensure a Metronome customer record exists for this user (fire-and-forget)
+    ensureMetronomeCustomer(user.id, email).catch(() => {})
+
     // Check  project
     const { data: existingProjects, error: countError } = await supabase
       .from("projects")
@@ -157,6 +161,12 @@ export async function POST(request: NextRequest) {
 
     console.log(`🎉 Project created: ${project.id} by user ${user.id}`)
 
+    // Ingest usage event into Metronome (fire-and-forget)
+    ingestUsageEvent(user.id, "project_created", {
+      project_id: project.id,
+      template_type,
+    }).catch(() => {})
+
     const response = NextResponse.json({
       projectId: project.id, // Add projectId for frontend compatibility
       project: {
diff --git a/apps/web/lib/metronome.ts b/apps/web/lib/metronome.ts
new file mode 100644
index 0000000..12292b6
--- /dev/null
+++ b/apps/web/lib/metronome.ts
@@ -0,0 +1,88 @@
+/**
+ * Metronome usage-based billing API client.
+ * https://docs.metronome.com
+ *
+ * All functions are no-ops when METRONOME_API_KEY is not set, so the
+ * integration is safe to deploy before the key is provisioned.
+ */
+
+const METRONOME_BASE = "https://api.metronome.com/v1"
+
+function getApiKey(): string | undefined {
+  return process.env.METRONOME_API_KEY
+}
+
+/**
+ * Idempotently ensure a Metronome customer exists for the given Supabase user.
+ * Uses the Supabase user ID as an `ingest_alias` so events can be attributed
+ * without separately storing the Metronome customer UUID.
+ *
+ * A 409 response is treated as success (customer already exists).
+ */
+export async function ensureMetronomeCustomer(userId: string, email: string): Promise<void> {
+  const apiKey = getApiKey()
+  if (!apiKey) return
+
+  try {
+    const res = await fetch(`${METRONOME_BASE}/customers`, {
+      method: "POST",
+      headers: {
+        Authorization: `Bearer ${apiKey}`,
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({
+        name: email,
+        ingest_aliases: [userId],
+      }),
+    })
+
+    if (!res.ok && res.status !== 409) {
+      console.error(`Metronome: ensureCustomer failed [${res.status}]`, await res.text())
+    }
+  } catch (err) {
+    console.error("Metronome: ensureCustomer error", err)
+  }
+}
+
+/**
+ * Ingest a usage event for the given user (identified by Supabase user ID,
+ * which must have been registered as an ingest_alias via ensureMetronomeCustomer).
+ *
+ * Failures are logged but never thrown — billing should never block the
+ * primary request path.
+ */
+export async function ingestUsageEvent(
+  userId: string,
+  eventType: string,
+  properties: Record<string, string | number | boolean> = {},
+): Promise<void> {
+  const apiKey = getApiKey()
+  if (!apiKey) return
+
+  try {
+    const res = await fetch(`${METRONOME_BASE}/ingest`, {
+      method: "POST",
+      headers: {
+        Authorization: `Bearer ${apiKey}`,
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({
+        events: [
+          {
+            transaction_id: `${userId}-${eventType}-${Date.now()}`,
+            customer_id: userId,
+            event_type: eventType,
+            timestamp: new Date().toISOString(),
+            properties,
+          },
+        ],
+      }),
+    })
+
+    if (!res.ok) {
+      console.error(`Metronome: ingest failed [${res.status}] for ${eventType}`, await res.text())
+    }
+  } catch (err) {
+    console.error(`Metronome: ingest error for ${eventType}`, err)
+  }
+}
diff --git a/env.example b/env.example
index 5e07bcd..a264639 100644
--- a/env.example
+++ b/env.example
@@ -38,6 +38,11 @@ NETLIFY_ACCESS_TOKEN=your-netlify-access-token
 # 21st.dev Subscription API (for subscription checks)
 SUBSCRIPTION_API_KEY=your-21st-dev-api-key
 
+# Metronome Usage-Based Billing (https://metronome.com)
+# Tracks usage events (project_created, etc.) per customer.
+# Leave unset to disable Metronome integration.
+METRONOME_API_KEY=your-metronome-api-key
+
 # Development: Skip subscription check (set to 'true' to bypass subscription validation in dev)
 SKIP_SUBSCRIPTION_CHECK=false