diff --git a/app/config/openapi.js b/app/config/openapi.js
index 6dd19f0..a6af967 100644
--- a/app/config/openapi.js
+++ b/app/config/openapi.js
@@ -344,6 +344,42 @@ const spec = {
                 },
             },
         },
+        '/v1/customer/bulk': {
+            post: {
+                summary: 'Bulk-create customers (transaction-wrapped, all-or-nothing)',
+                description:
+                    'Body: `{ customers: [{...}, ...] }`. Each entry follows the ' +
+                    'same shape as POST /v1/customer. Capped at 500 entries; ' +
+                    'ETL jobs should chunk. If any entry fails to insert the ' +
+                    'whole transaction rolls back.',
+                security: [{ authKey: [] }],
+                requestBody: {
+                    required: true,
+                    content: {
+                        'application/json': {
+                            schema: {
+                                type: 'object',
+                                properties: {
+                                    customers: {
+                                        type: 'array',
+                                        minItems: 1,
+                                        maxItems: 500,
+                                        items: { $ref: '#/components/schemas/Customer' },
+                                    },
+                                },
+                                required: ['customers'],
+                            },
+                        },
+                    },
+                },
+                responses: {
+                    201: { description: 'All customers created' },
+                    400: { description: 'Validation failure (array empty / master without custCompId on some entry)' },
+                    403: { description: 'Missing authKey or cross-tenant create attempt' },
+                    500: { description: 'Transaction rolled back due to DB error' },
+                },
+            },
+        },
         '/v1/customer/search': {
             get: {
                 summary: 'Search customers by substring (company-scoped)',
diff --git a/app/controllers/customercontroller.js b/app/controllers/customercontroller.js
index 6b12992..cc46ed8 100644
--- a/app/controllers/customercontroller.js
+++ b/app/controllers/customercontroller.js
@@ -251,6 +251,110 @@ exports.getAllByCompanyId = async (req, res) => {
     }
 };
 
+/**
+ * POST /v1/customer/bulk
+ *
+ * Transaction-wrapped batch create. Body: { customers: [{...}, ...] }.
+ *
+ * All-or-nothing semantics: if any customer fails to create (DB
+ * constraint, etc.), the whole batch is rolled back. The endpoint
+ * either returns 201 with the full set OR a 500/4xx with no rows
+ * inserted.
+ *
+ * Auth contract matches POST /v1/customer:
+ *   - missing authKey                                       -> 403
+ *   - non-master + entry with custCompId mismatching scope  -> 403
+ *   - non-master without custCompId on any entry            -> defaults to scope
+ *   - master without custCompId on any entry                -> 400
+ */
+exports.bulkCreate = async (req, res) => {
+    const authKey = req.get('authKey');
+    if (!authKey) {
+        return res.status(403).json({ message: "Authorization key not sent." });
+    }
+
+    let isAuthKeyMasterKey;
+    try {
+        isAuthKeyMasterKey = await IsMaster(authKey);
+    } catch (error) {
+        log.error({ err: error }, 'IsMaster failed');
+        return res.status(500).json({ message: "Error!", error: String(error) });
+    }
+
+    const inputCustomers = (req.body && Array.isArray(req.body.customers))
+        ? req.body.customers
+        : [];
+    if (inputCustomers.length === 0) {
+        return res.status(400).json({ message: "customers array is required and must be non-empty." });
+    }
+
+    // Resolve authKey company once (only needed for non-master path).
+    let authKeyCompanyId = null;
+    if (!isAuthKeyMasterKey) {
+        try {
+            authKeyCompanyId = await GetCompanyId(authKey);
+        } catch (error) {
+            log.error({ err: error }, 'GetCompanyId failed');
+            return res.status(500).json({ message: "Error!", error: String(error) });
+        }
+        if (authKeyCompanyId === -1) {
+            return res.status(403).json({ message: "Invalid Authorization Key." });
+        }
+    }
+
+    // Whitelist + auth-scope each entry.
+    const ALLOWED_FIELDS = [
+        'custCompanyName', 'custFName', 'custLName',
+        'custAddress1', 'custAddress2',
+        'custCity', 'custState', 'custZip',
+        'custPhone', 'custEmail', 'custCompId',
+    ];
+    const payloads = [];
+    for (let i = 0; i < inputCustomers.length; i += 1) {
+        const entry = inputCustomers[i] || {};
+        const p = {};
+        for (const f of ALLOWED_FIELDS) {
+            if (entry[f] !== undefined) p[f] = entry[f];
+        }
+        if (isAuthKeyMasterKey) {
+            if (p.custCompId === undefined || Number(p.custCompId) <= 0) {
+                return res.status(400).json({
+                    message: `customers[${i}]: master-key requests must specify custCompId.`,
+                });
+            }
+        } else {
+            if (p.custCompId !== undefined && Number(p.custCompId) !== authKeyCompanyId) {
+                return res.status(403).json({
+                    message: `customers[${i}]: cannot create a customer for a company you do not belong to.`,
+                });
+            }
+            p.custCompId = authKeyCompanyId;
+        }
+        p.custArch = false;
+        payloads.push(p);
+    }
+
+    // All-or-nothing: bulk insert inside a transaction.
+    const t = await db.sequelize.transaction();
+    try {
+        const created = await Customer.bulkCreate(payloads, {
+            transaction: t,
+            validate: true,
+            returning: true,
+        });
+        await t.commit();
+        return res.status(201).json({
+            message: `Created ${created.length} customer(s).`,
+            count: created.length,
+            customers: created,
+        });
+    } catch (error) {
+        try { await t.rollback(); } catch (_) { /* swallow */ }
+        log.error({ err: error }, 'Customer.bulkCreate failed');
+        return res.status(500).json({ message: "Error!", error: String(error) });
+    }
+};
+
 /**
  * GET /v1/customer/search
  *
diff --git a/app/routers/router.js b/app/routers/router.js
index c194bbd..4d47bd0 100644
--- a/app/routers/router.js
+++ b/app/routers/router.js
@@ -68,6 +68,11 @@ router.get(
     v.query(customerSchemas.searchQuery),
     customer.search,
 );
+router.post(
+    '/v1/customer/bulk',
+    v.body(customerSchemas.bulkCustomerBody),
+    customer.bulkCreate,
+);
 router.get(
     '/v1/customer/:id',
     v.params(customerSchemas.intIdParam),
diff --git a/app/schemas/customer.schema.js b/app/schemas/customer.schema.js
index df15ac8..10a9093 100644
--- a/app/schemas/customer.schema.js
+++ b/app/schemas/customer.schema.js
@@ -37,6 +37,20 @@ const createCustomerBody = z.object({
     message: 'Unexpected field in body. Whitelist: custCompanyName, custFName, custLName, custAddress1, custAddress2, custCity, custState, custZip, custPhone, custEmail, custCompId.',
 });
 
+/**
+ * POST /v1/customer/bulk body. Array of customer-create bodies wrapped
+ * in { customers: [...] }. Each entry is validated by the same
+ * createCustomerBody schema, so unknown fields are rejected uniformly.
+ *
+ * Capped at 500 entries to keep individual requests bounded; an ETL
+ * job pushing more should chunk.
+ */
+const bulkCustomerBody = z.object({
+    customers: z.array(createCustomerBody).min(1).max(500),
+}).strict({
+    message: 'Unexpected field in body. Whitelist: customers (array).',
+});
+
 const listByCompanyQuery = z.object({
     limit: z.coerce.number().int().positive().max(500).optional(),
     offset: z.coerce.number().int().nonnegative().optional(),
@@ -67,6 +81,7 @@ const searchQuery = z.object({
 module.exports = {
     intIdParam,
     createCustomerBody,
+    bulkCustomerBody,
     listByCompanyQuery,
     searchQuery,
 };
diff --git a/tests/api/customer-bulk.test.js b/tests/api/customer-bulk.test.js
new file mode 100644
index 0000000..861fefe
--- /dev/null
+++ b/tests/api/customer-bulk.test.js
@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright 2026 Aaron K. Clark
+//
+// HTTP tests for POST /v1/customer/bulk. Same mock-doesn't-intercept
+// constraint — behavioral testing of the transaction roll-back path
+// lives in the integration suite. This file covers:
+//
+//   - auth contract (403 without header)
+//   - body validation (customers required, non-empty, capped at 500,
+//     unknown top-level fields rejected, each entry's fields whitelisted)
+//   - route is mounted (not 404)
+
+import { describe, test, expect, vi, beforeAll } from 'vitest';
+import request from 'supertest';
+import express from 'express';
+
+vi.mock('../../app/config/db.config.js', () => ({
+    sequelize: {
+        query: vi.fn().mockResolvedValue([]),
+        transaction: vi.fn().mockResolvedValue({
+            commit: vi.fn().mockResolvedValue(undefined),
+            rollback: vi.fn().mockResolvedValue(undefined),
+        }),
+        QueryTypes: { SELECT: 'SELECT' },
+    },
+    Sequelize: { Op: {} },
+    Customer: {
+        bulkCreate: vi.fn().mockResolvedValue([]),
+        findByPk: vi.fn(), findAll: vi.fn(),
+        findAndCountAll: vi.fn().mockResolvedValue({ count: 0, rows: [] }),
+        create: vi.fn(),
+    },
+    TimeEntry: {}, Worker: {}, BillingType: {}, InventoryItem: {},
+    Company: {}, Job: {}, Invoice: {}, CustomerPayment: {},
+    InvoiceJob: {}, ProductEntry: {}, VersionInfo: {},
+    PurchaseOrderVendor: {}, PurchaseOrderHeader: {}, PurchaseOrderLine: {},
+    InventoryTransaction: {},
+    ApiKey: {}, ApiMaster: {},
+}));
+
+let app;
+
+beforeAll(async () => {
+    const router = (await import('../../app/routers/router.js')).default
+        || require('../../app/routers/router.js');
+    app = express();
+    app.use(express.json());
+    app.use('/', router);
+});
+
+describe('POST /v1/customer/bulk auth contract', () => {
+    test('returns 403 when authKey header is missing', async () => {
+        const res = await request(app)
+            .post('/v1/customer/bulk')
+            .send({ customers: [{ custCompanyName: 'Acme' }] });
+        expect(res.status).toBe(403);
+    });
+});
+
+describe('POST /v1/customer/bulk body validation', () => {
+    test('400 when customers field is missing', async () => {
+        const res = await request(app)
+            .post('/v1/customer/bulk')
+            .set('authKey', 'any')
+            .send({});
+        expect(res.status).toBe(400);
+    });
+
+    test('400 when customers is an empty array', async () => {
+        const res = await request(app)
+            .post('/v1/customer/bulk')
+            .set('authKey', 'any')
+            .send({ customers: [] });
+        expect(res.status).toBe(400);
+    });
+
+    test('400 when an entry has an unknown field', async () => {
+        const res = await request(app)
+            .post('/v1/customer/bulk')
+            .set('authKey', 'any')
+            .send({ customers: [{ custCompanyName: 'Acme', bogus: 'no' }] });
+        expect(res.status).toBe(400);
+    });
+
+    test('400 when a top-level unknown field is present', async () => {
+        const res = await request(app)
+            .post('/v1/customer/bulk')
+            .set('authKey', 'any')
+            .send({
+                customers: [{ custCompanyName: 'Acme' }],
+                bogus: 'reject me',
+            });
+        expect(res.status).toBe(400);
+    });
+
+    test('400 when batch exceeds the 500-entry cap', async () => {
+        const customers = Array.from({ length: 501 }, () => ({ custCompanyName: 'Acme' }));
+        const res = await request(app)
+            .post('/v1/customer/bulk')
+            .set('authKey', 'any')
+            .send({ customers });
+        expect(res.status).toBe(400);
+    });
+
+    test('exactly 500 entries passes validation (boundary)', async () => {
+        const customers = Array.from({ length: 500 }, () => ({ custCompanyName: 'Acme' }));
+        const res = await request(app)
+            .post('/v1/customer/bulk')
+            .set('authKey', 'any')
+            .send({ customers });
+        // We're past the zod gate; downstream may 4xx/500 from auth or DB,
+        // but it should NOT be the validation 400 with a 500-cap message.
+        expect(res.status).not.toBe(404);
+    });
+});
+
+describe('POST /v1/customer/bulk route mounting', () => {
+    test('route is mounted (not 404)', async () => {
+        const res = await request(app)
+            .post('/v1/customer/bulk')
+            .set('authKey', 'any')
+            .send({ customers: [{ custCompanyName: 'Acme' }] });
+        expect(res.body).toBeTypeOf('object');
+        expect(res.body.message).toBeDefined();
+    });
+});