diff --git a/hailbytes-vuln-calculator.js b/hailbytes-vuln-calculator.js
index 1d2c2aa..d875174 100644
--- a/hailbytes-vuln-calculator.js
+++ b/hailbytes-vuln-calculator.js
@@ -550,8 +550,7 @@ const STYLES = `
 
 // ─── Template ─────────────────────────────────────────────────────────────────
 
-const TMPL = document.createElement('template');
-TMPL.innerHTML = `<style>${STYLES}</style>
+const TEMPLATE_HTML = `<style>${STYLES}</style>
 <div class="header">
   <h1><span class="icon">🔍</span> Vulnerability Scanner Infrastructure Calculator <span class="hailbytes-badge">HailBytes</span></h1>
   <p>Size your scanning infrastructure — estimate VM requirements, cloud costs, and ROI entirely in the browser</p>
@@ -644,13 +643,28 @@ TMPL.innerHTML = `<style>${STYLES}</style>
 
 // ─── Web Component ────────────────────────────────────────────────────────────
 
-class HailbytesVulnCalculator extends HTMLElement {
+// The component depends on the DOM, but the exported `calculate()` does not.
+// Build the <template> lazily (on first construction) and fall back to a plain
+// base class when HTMLElement is unavailable, so this module can be imported in
+// Node / SSR environments without throwing — see calculate() below.
+let TMPL = null;
+function getTemplate() {
+  if (!TMPL) {
+    TMPL = document.createElement('template');
+    TMPL.innerHTML = TEMPLATE_HTML;
+  }
+  return TMPL;
+}
+
+const BaseElement = typeof HTMLElement !== 'undefined' ? HTMLElement : class {};
+
+class HailbytesVulnCalculator extends BaseElement {
   static get observedAttributes() { return ['theme', 'branding']; }
 
   constructor() {
     super();
     this._shadow = this.attachShadow({ mode: 'open' });
-    this._shadow.appendChild(TMPL.content.cloneNode(true));
+    this._shadow.appendChild(getTemplate().content.cloneNode(true));
     this._lastResult = null;
   }
 
@@ -856,7 +870,11 @@ class HailbytesVulnCalculator extends HTMLElement {
   }
 }
 
-customElements.define('hailbytes-vuln-calculator', HailbytesVulnCalculator);
+// Only register the custom element when running in a browser-like environment.
+// Importing the module purely for calculate() (Node, SSR) must not throw.
+if (typeof customElements !== 'undefined' && typeof HTMLElement !== 'undefined') {
+  customElements.define('hailbytes-vuln-calculator', HailbytesVulnCalculator);
+}
 
 export default HailbytesVulnCalculator;
 export { HailbytesVulnCalculator, calculateResources as calculate };
diff --git a/test/smoke.test.mjs b/test/smoke.test.mjs
index 5573ccf..dcbb390 100644
--- a/test/smoke.test.mjs
+++ b/test/smoke.test.mjs
@@ -3,6 +3,8 @@
 
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
+import { execFileSync } from 'node:child_process';
+import { fileURLToPath } from 'node:url';
 
 class FakeElement {
   constructor() { this.children = []; this.style = {}; this.classList = { add(){}, remove(){}, toggle(){} }; }
@@ -78,6 +80,32 @@ test('calculate() recognises HailBytes ASM tool', () => {
   assert.equal(r.has_asm, true);
 });
 
+// Regression guard: the module must be importable — and calculate() usable —
+// in a pure Node / SSR environment with no DOM globals. The tests above install
+// a DOM shim on globalThis, so we spawn a fresh, unshimmed Node process to prove
+// importing the module no longer touches `document`/`HTMLElement` at load time.
+test('module imports and calculate() runs in a pure Node environment (no DOM shim)', () => {
+  const moduleUrl = new URL('../hailbytes-vuln-calculator.js', import.meta.url).href;
+  const script = `
+    import { calculate, default as Component } from ${JSON.stringify(moduleUrl)};
+    if (typeof calculate !== 'function') { console.error('calculate not a function'); process.exit(1); }
+    if (typeof Component !== 'function') { console.error('default export not a class'); process.exit(1); }
+    const r = calculate({
+      target_hosts: 1000, scan_intensity: 'medium', scan_frequency: 'weekly',
+      scan_window: 8, scanning_tools: ['hailbytes_asm'], compliance_needs: [],
+    });
+    if (!r || !r.vm_resources || typeof r.vm_resources.cpu_cores !== 'number') {
+      console.error('unexpected result shape'); process.exit(1);
+    }
+    console.log('PURE_OK');
+  `;
+  const out = execFileSync(process.execPath, ['--input-type=module', '-e', script], {
+    encoding: 'utf8',
+    cwd: fileURLToPath(new URL('.', import.meta.url)),
+  });
+  assert.match(out, /PURE_OK/);
+});
+
 test('class declares observedAttributes including theme and branding', () => {
   const observed = mod.default.observedAttributes;
   assert.ok(Array.isArray(observed));