diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..0976e48
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,54 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  node:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node-version: [20, 22, 24]
+    
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          registry-url: 'https://registry.npmjs.org'
+          cache: 'npm'
+
+      - name: Install deps
+        run: npm ci
+
+      - name: Build
+        run: npm run build
+
+      - name: Run Node.js tests
+        run: npm test
+
+  bun:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
+
+      - name: Install deps
+        run: npm ci
+
+      - name: Build
+        run: bun run build
+
+      - name: Run Bun tests
+        run: bun test
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 8be3996..4c95eff 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -19,6 +19,7 @@ jobs:
         with:
           node-version: '22.x'
           registry-url: 'https://registry.npmjs.org'
+          cache: 'npm'
 
       - name: Ensure package version is 3.x.x
         run: |
@@ -28,7 +29,8 @@ jobs:
             3.*) echo "OK: version is 3.x.x" ;;
             *) echo "ERROR: package.json version must be 3.x.x for v3 tags" && exit 1 ;;
           esac
+
       - name: Publish to NPM with dist-tag "latest"
         run: npm run prepack && npm publish --tag latest --//registry.npmjs.org/:_authToken="$NPM_TOKEN"
         env:
-          NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
\ No newline at end of file
+          NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
diff --git a/.gitignore b/.gitignore
index 76588e4..47b1694 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,7 @@
 node_modules
 *js
+!test/fixtures/**/*.mjs
+!test/scripts/**/*.mjs
 cjs
 esm
 .idea
diff --git a/package.json b/package.json
index 5b1d0c2..27666cd 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,7 @@
   "description": "A library for integrating with Chargebee.",
   "scripts": {
     "prepack": "npm install && npm run build",
-    "test": "mocha -r ts-node/register 'test/**/*.test.ts'",
+    "test": "TS_NODE_PROJECT=./tsconfig.test.json mocha -r ts-node/register 'test/**/*.test.ts'",
     "build": "npm run build-esm && npm run build-cjs",
     "build-esm": "rm -rf esm && mkdir -p esm && tsc -p tsconfig.esm.json && echo '{\"type\":\"module\"}' > esm/package.json",
     "build-cjs": "rm -rf cjs && mkdir -p cjs && tsc -p tsconfig.cjs.json && echo '{\"type\":\"commonjs\"}' > cjs/package.json",
diff --git a/test/fixtures/load-esm-worker-bundle.mjs b/test/fixtures/load-esm-worker-bundle.mjs
new file mode 100644
index 0000000..e5ecac9
--- /dev/null
+++ b/test/fixtures/load-esm-worker-bundle.mjs
@@ -0,0 +1,36 @@
+/**
+ * Runs inside a Node worker thread ({ type: 'module' }) to ensure the ESM
+ * worker bundle parses and exposes webhook exports in an isolated context.
+ */
+import { parentPort, workerData } from 'node:worker_threads';
+import { pathToFileURL } from 'node:url';
+import path from 'node:path';
+
+const required = [
+  'default',
+  'WebhookEventType',
+  'WebhookContentType',
+  'basicAuthValidator',
+  'WebhookError',
+  'WebhookAuthenticationError',
+  'WebhookPayloadValidationError',
+  'WebhookPayloadParseError',
+];
+
+try {
+  const root = workerData.root;
+  const bundlePath = path.join(root, 'esm/chargebee.esm.worker.js');
+  const mod = await import(pathToFileURL(bundlePath).href);
+  const missing = required.filter((k) => mod[k] === undefined);
+  if (missing.length) {
+    parentPort.postMessage({ ok: false, error: 'missing exports', missing });
+  } else {
+    parentPort.postMessage({ ok: true });
+  }
+} catch (err) {
+  parentPort.postMessage({
+    ok: false,
+    error: err instanceof Error ? err.message : String(err),
+    stack: err instanceof Error ? err.stack : undefined,
+  });
+}
diff --git a/test/worker-bundle.test.ts b/test/worker-bundle.test.ts
new file mode 100644
index 0000000..862b9fb
--- /dev/null
+++ b/test/worker-bundle.test.ts
@@ -0,0 +1,116 @@
+import { expect } from 'chai';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import { fileURLToPath, pathToFileURL } from 'node:url';
+import { Worker } from 'node:worker_threads';
+
+/** `type` is supported at runtime for ESM workers; widen options until typings always include it. */
+type WorkerThreadOptions = NonNullable<ConstructorParameters<typeof Worker>[1]> & {
+  type?: 'module' | 'classic';
+};
+
+const testDir = path.resolve(process.cwd(), 'test');
+const repoRoot = path.join(testDir, '..');
+const esmWorkerPath = path.join(repoRoot, 'esm/chargebee.esm.worker.js');
+
+const hasBuiltEsmWorker = fs.existsSync(esmWorkerPath);
+
+function describeIfEsmBuilt(title: string, fn: () => void): void {
+  if (hasBuiltEsmWorker) {
+    describe(title, fn);
+    return;
+  }
+  describe.skip(
+    `${title} (skipped: run \`npm run build\` or \`npm run test:worker-bundle\`)`,
+    fn,
+  );
+}
+
+const REQUIRED_VALUE_EXPORTS = [
+  'WebhookEventType',
+  'WebhookContentType',
+  'basicAuthValidator',
+  'WebhookError',
+  'WebhookAuthenticationError',
+  'WebhookPayloadValidationError',
+  'WebhookPayloadParseError',
+] as const;
+
+function assertWebhookExports(mod: Record<string, unknown>, label: string): void {
+  for (const name of REQUIRED_VALUE_EXPORTS) {
+    expect(mod, `${label} must export ${name}`).to.have.property(name);
+    expect(mod[name], `${label}.${name}`).to.not.equal(undefined);
+  }
+
+  expect(mod.default, `${label} default export`).to.be.a('function');
+  expect(mod.WebhookEventType, `${label}.WebhookEventType`).to.be.an('object');
+  expect(mod.WebhookContentType, `${label}.WebhookContentType`).to.equal(mod.WebhookEventType);
+  expect(mod.basicAuthValidator, `${label}.basicAuthValidator`).to.be.a('function');
+
+  const Err = mod.WebhookError as typeof Error;
+  expect(new Err('x')).to.be.instanceof(Error);
+  expect((new Err('x') as Error).name).to.equal('WebhookError');
+
+  const AuthErr = mod.WebhookAuthenticationError as typeof Error;
+  expect(new AuthErr('a')).to.be.instanceof(Err);
+
+  const ValErr = mod.WebhookPayloadValidationError as typeof Error;
+  expect(new ValErr('v')).to.be.instanceof(Err);
+
+  const ParseErr = mod.WebhookPayloadParseError as typeof Error;
+  expect(new ParseErr('p')).to.be.instanceof(Err);
+}
+
+describeIfEsmBuilt('Worker entry bundle (ESM)', () => {
+  it('exposes webhook value exports from built ESM worker entry', async function () {
+    try {
+      const mod = (await import(pathToFileURL(esmWorkerPath).href)) as Record<string, unknown>;
+      assertWebhookExports(mod, 'esm/chargebee.esm.worker.js');
+    } catch (error) {
+      const mod = require(esmWorkerPath);
+      assertWebhookExports(mod, 'esm/chargebee.esm.worker.js');
+    }
+  });
+});
+
+describeIfEsmBuilt('Worker thread can load ESM worker bundle', () => {
+  it('parses the bundle and receives all webhook exports inside a worker', function (done) {
+    const fixture = path.join(testDir, 'fixtures', 'load-esm-worker-bundle.mjs');
+    const workerOptions: WorkerThreadOptions = {
+      workerData: { root: repoRoot },
+      type: 'module',
+    };
+    const worker = new Worker(fixture, workerOptions);
+    let settled = false;
+    const finish = (err?: Error): void => {
+      if (settled) {
+        return;
+      }
+      settled = true;
+      void worker.terminate().finally(() => {
+        if (err) {
+          done(err);
+        } else {
+          done();
+        }
+      });
+    };
+    worker.on('message', (msg: { ok: boolean; error?: string; missing?: string[]; stack?: string }) => {
+      try {
+        expect(msg.ok, JSON.stringify(msg)).to.be.true;
+        finish();
+      } catch (e) {
+        finish(e as Error);
+      }
+    });
+    worker.on('error', finish);
+    worker.on('exit', (code) => {
+      if (settled) {
+        return;
+      }
+      if (code !== 0) {
+        finish(new Error(`worker exited with code ${code}`));
+      }
+    });
+  });
+});
diff --git a/tsconfig.test.json b/tsconfig.test.json
new file mode 100644
index 0000000..0fdfe8d
--- /dev/null
+++ b/tsconfig.test.json
@@ -0,0 +1,20 @@
+{
+  "compilerOptions": {
+    "noEmit": true,
+    "rootDir": ".",
+    "module": "ES2022",
+    "moduleResolution": "node",
+    "target": "ES2022",
+    "types": ["node", "mocha"],
+    "esModuleInterop": true,
+    "allowSyntheticDefaultImports": true
+  },
+  "include": ["src/**/*.ts", "test/**/*.ts"],
+  "ts-node": {
+    "experimentalResolver": true,
+    "compilerOptions": {
+      "module": "CommonJS",
+      "moduleResolution": "node"
+    }
+  }
+}