diff --git a/packages/paykit/src/webhook/__tests__/webhook.api.test.ts b/packages/paykit/src/webhook/__tests__/webhook.api.test.ts
new file mode 100644
index 00000000..29e9c0c2
--- /dev/null
+++ b/packages/paykit/src/webhook/__tests__/webhook.api.test.ts
@@ -0,0 +1,50 @@
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+
+import { shouldAllowUnsignedPayload } from "../webhook.api";
+
+// shouldAllowUnsignedPayload gates whether the public webhook endpoint skips
+// Stripe signature verification entirely. It must only ever be true because
+// an operator explicitly opted in, never because of the server's ambient
+// NODE_ENV - see the comment on the function for why.
+describe("shouldAllowUnsignedPayload", () => {
+  const originalEnv = { ...process.env };
+
+  beforeEach(() => {
+    delete process.env.PAYKIT_ALLOW_UNSIGNED_PAYLOADS;
+    delete process.env.PAYKIT_ALLOW_STALE_SIGNATURES;
+    delete process.env.NODE_ENV;
+  });
+
+  afterEach(() => {
+    process.env = { ...originalEnv };
+  });
+
+  it("requires the cloud-replay header even with an explicit opt-in", () => {
+    process.env.PAYKIT_ALLOW_UNSIGNED_PAYLOADS = "1";
+    expect(shouldAllowUnsignedPayload(new Headers())).toBe(false);
+  });
+
+  it("does not allow unsigned payloads from NODE_ENV=development alone", () => {
+    process.env.NODE_ENV = "development";
+    const headers = new Headers({ "x-paykit-cloud-replay": "1" });
+    expect(shouldAllowUnsignedPayload(headers)).toBe(false);
+  });
+
+  it("does not allow unsigned payloads from NODE_ENV=test alone", () => {
+    process.env.NODE_ENV = "test";
+    const headers = new Headers({ "x-paykit-cloud-replay": "1" });
+    expect(shouldAllowUnsignedPayload(headers)).toBe(false);
+  });
+
+  it("allows unsigned payloads with the documented opt-in flag", () => {
+    process.env.PAYKIT_ALLOW_UNSIGNED_PAYLOADS = "1";
+    const headers = new Headers({ "x-paykit-cloud-replay": "1" });
+    expect(shouldAllowUnsignedPayload(headers)).toBe(true);
+  });
+
+  it("allows unsigned payloads with the legacy alias flag", () => {
+    process.env.PAYKIT_ALLOW_STALE_SIGNATURES = "1";
+    const headers = new Headers({ "x-paykit-cloud-replay": "1" });
+    expect(shouldAllowUnsignedPayload(headers)).toBe(true);
+  });
+});
diff --git a/packages/paykit/src/webhook/webhook.api.ts b/packages/paykit/src/webhook/webhook.api.ts
index 16490805..bed56c67 100644
--- a/packages/paykit/src/webhook/webhook.api.ts
+++ b/packages/paykit/src/webhook/webhook.api.ts
@@ -9,7 +9,18 @@ function headersToRecord(headers: Headers): Record<string, string> {
   return result;
 }
 
-function shouldAllowUnsignedPayload(headers: Headers): boolean {
+/**
+ * Whether an incoming request may skip Stripe signature verification. Only the
+ * explicit opt-in env vars gate this: NODE_ENV isn't a reliable signal for
+ * "this deployment is safe to leave unauthenticated". Self-hosted containers
+ * and staging environments routinely run without NODE_ENV=production, or with
+ * it set to "development"/"test", while still processing real webhooks - and
+ * this endpoint has no other authentication, so treating NODE_ENV as consent
+ * turned the `x-paykit-cloud-replay` header into an unauthenticated way to
+ * post forged, fully-trusted billing events (subscriptions, invoices,
+ * payments) on any such deployment.
+ */
+export function shouldAllowUnsignedPayload(headers: Headers): boolean {
   if (headers.get("x-paykit-cloud-replay") !== "1") {
     return false;
   }
@@ -17,9 +28,7 @@ function shouldAllowUnsignedPayload(headers: Headers): boolean {
   return (
     process.env.PAYKIT_ALLOW_UNSIGNED_PAYLOADS === "1" ||
     // Legacy alias kept for local replay compatibility; remove in a future major.
-    process.env.PAYKIT_ALLOW_STALE_SIGNATURES === "1" ||
-    process.env.NODE_ENV === "development" ||
-    process.env.NODE_ENV === "test"
+    process.env.PAYKIT_ALLOW_STALE_SIGNATURES === "1"
   );
 }