diff --git a/src/components/dice-tray.js b/src/components/dice-tray.js
index f080334..594e3a3 100644
--- a/src/components/dice-tray.js
+++ b/src/components/dice-tray.js
@@ -1,5 +1,5 @@
 import { rollPool } from '../dice/roller.js';
-import { getRulePack } from '../dice/rulepacks/index.js';
+import { getRulePack, listRulePacks } from '../dice/rulepacks/index.js';
 
 const DICE = [4, 6, 8, 10, 12, 20, 100];
 
@@ -17,10 +17,23 @@ export class DiceTray extends HTMLElement {
   set sides(v) { this._sides = Number(v); this.render(); }
   get count() { return this._count; }
   set count(v) { this._count = Number(v); }
-  set systemId(v) { this._systemId = v; }
+  set systemId(v) { this._systemId = v; this.render(); }
   get systemId() { return this._systemId; }
 
-  connectedCallback() { this.render(); }
+  connectedCallback() { this.render(); this.syncParams(); }
+
+  syncParams() {
+    const pack = getRulePack(this._systemId);
+    const next = {};
+    if (pack && pack.params) {
+      for (const p of pack.params) {
+        const input = this.querySelector(`[data-param="${p.key}"]`);
+        const raw = input ? input.value : '';
+        next[p.key] = raw === '' ? p.default : Number(raw);
+      }
+    }
+    this.params = next;
+  }
 
   roll() {
     const { results, total } = rollPool([{ sides: this._sides, count: this._count }], this.rng);
@@ -42,9 +55,18 @@ export class DiceTray extends HTMLElement {
       ? (pack && pack.summary ? pack.summary(this.last.verdict) : '')
       : '';
 
+    const packs = listRulePacks();
+    const packBar = [{ id: '', label: 'Any die' }, ...packs].map((p) =>
+      `<button class="pack ${p.id === this._systemId ? 'on' : ''}" data-pack-id="${p.id}">${p.label}</button>`).join('');
+    const active = getRulePack(this._systemId);
+    const paramInputs = (active && active.params ? active.params : []).map((p) =>
+      `<label class="param">${p.label}<input type="number" data-param="${p.key}" value="${this.params[p.key] ?? p.default}" /></label>`).join('');
+
     this.innerHTML = `
       <div class="dice-tray">
+        <div class="pack-bar">${packBar}</div>
         <div class="picker">${picker}</div>
+        <div class="params">${paramInputs}</div>
         <div class="felt">${felt}</div>
         <div class="verdict" data-role="verdict">${verdict}</div>
         <button class="roll" data-role="roll">Roll</button>
@@ -52,6 +74,10 @@ export class DiceTray extends HTMLElement {
 
     this.querySelectorAll('[data-sides]').forEach((b) =>
       b.addEventListener('click', () => { this.sides = Number(b.dataset.sides); }));
+    this.querySelectorAll('[data-pack-id]').forEach((b) =>
+      b.addEventListener('click', () => { this._systemId = b.dataset.packId; this.syncParams(); this.render(); }));
+    this.querySelectorAll('[data-param]').forEach((inp) =>
+      inp.addEventListener('input', () => this.syncParams()));
     this.querySelector('[data-role=roll]').addEventListener('click', () => this.roll());
   }
 }
diff --git a/src/styles.css b/src/styles.css
index a877c95..16fae5d 100644
--- a/src/styles.css
+++ b/src/styles.css
@@ -55,3 +55,9 @@ gm-shell { display: block; }
 .prop-overlay { position: fixed; inset: 0; background: #000000ee; display: flex; align-items: center; justify-content: center; z-index: 100; }
 .prop-img { max-width: 96vw; max-height: 96vh; object-fit: contain; }
 prop-viewer[hidden] { display: none; }
+.pack-bar { display: flex; gap: 6px; flex-wrap: wrap; margin-bottom: 8px; }
+.pack { font-size: 11px; padding: 5px 10px; border-radius: 20px; border: 1px solid #2b3644; background: #161d27; color: #9fb0c2; }
+.pack.on { background: #1e3a52; border-color: #3f7fb0; color: #dcefff; }
+.params { display: flex; gap: 10px; flex-wrap: wrap; margin: 8px 0; }
+.param { font-size: 11px; color: #9fb0c2; display: flex; flex-direction: column; gap: 3px; }
+.param input { width: 80px; background: #161d27; border: 1px solid #2a3542; border-radius: 6px; padding: 6px 8px; color: #e7eef6; }
diff --git a/tests/components/dice-tray-packs.test.js b/tests/components/dice-tray-packs.test.js
new file mode 100644
index 0000000..dbfaf80
--- /dev/null
+++ b/tests/components/dice-tray-packs.test.js
@@ -0,0 +1,46 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import '../../src/components/dice-tray.js';
+
+const seq = (vals) => { let i = 0; return () => vals[i++ % vals.length]; };
+
+describe('<dice-tray> pack selector + params', () => {
+  let el;
+  beforeEach(() => {
+    document.body.innerHTML = '';
+    el = document.createElement('dice-tray');
+    document.body.appendChild(el);
+  });
+
+  it('renders a button for each registered pack plus Any die', () => {
+    expect(el.querySelector('[data-pack-id="coc-coc-d100"]') || el.querySelector('[data-pack-id="coc-d100"]')).not.toBe(null);
+    expect(el.querySelector('[data-pack-id="vanity-d6"]')).not.toBe(null);
+    expect(el.querySelector('[data-pack-id=""]')).not.toBe(null); // Any die
+  });
+
+  it('selecting a pack updates systemId and shows its param inputs', () => {
+    el.querySelector('[data-pack-id="coc-d100"]').click();
+    expect(el.systemId).toBe('coc-d100');
+    expect(el.querySelector('[data-param="target"]')).not.toBe(null);
+  });
+
+  it('feeds param inputs into interpret and renders the pack summary', () => {
+    el.querySelector('[data-pack-id="coc-d100"]').click();
+    el.sides = 100; el.count = 1;
+    el.querySelector('[data-param="target"]').value = '40';
+    el.querySelector('[data-param="target"]').dispatchEvent(new Event('input'));
+    el.rng = seq([0.95]); // d100 -> floor(0.95*100)+1 = 96
+    el.roll();
+    expect(el.last.verdict.target).toBe(40);
+    expect(el.last.verdict.level).toBe('fumble'); // 96 with target 40
+    expect(el.querySelector('[data-role=verdict]').textContent).toContain('FUMBLE');
+  });
+
+  it('Any die selection clears the rule-pack (blank verdict)', () => {
+    el.querySelector('[data-pack-id=""]').click();
+    expect(el.systemId).toBe('');
+    el.sides = 20; el.count = 1; el.rng = seq([0.5]);
+    el.roll();
+    expect(el.last.verdict).toBe(null);
+    expect(el.querySelector('[data-role=verdict]').textContent).toBe('');
+  });
+});