diff --git a/src/lib/server/system-name.spec.ts b/src/lib/server/system-name.spec.ts
new file mode 100644
index 0000000..d40cba9
--- /dev/null
+++ b/src/lib/server/system-name.spec.ts
@@ -0,0 +1,115 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+vi.mock('$lib/db', () => ({
+	prisma: {
+		licenseKey: { findFirst: vi.fn(), update: vi.fn() }
+	}
+}));
+
+import { prisma } from '$lib/db';
+import { applySystemName, normalizeSystemName, SYSTEM_NAME_MAX_LENGTH } from './system-name';
+
+const keyFindFirst = prisma.licenseKey.findFirst as ReturnType<typeof vi.fn>;
+const keyUpdate = prisma.licenseKey.update as ReturnType<typeof vi.fn>;
+
+beforeEach(() => {
+	vi.clearAllMocks();
+});
+
+describe('normalizeSystemName', () => {
+	it('trims and returns a case-folded copy', () => {
+		expect(normalizeSystemName('  Living Room  ')).toEqual({
+			ok: true,
+			name: 'Living Room',
+			lower: 'living room'
+		});
+	});
+
+	it('accepts the length bounds', () => {
+		expect(normalizeSystemName('a'.repeat(SYSTEM_NAME_MAX_LENGTH)).ok).toBe(true);
+		expect(normalizeSystemName('a')).toEqual({ ok: true, name: 'a', lower: 'a' });
+	});
+
+	it('rejects empty, whitespace, and out-of-range values', () => {
+		expect(normalizeSystemName('')).toEqual({ ok: false });
+		expect(normalizeSystemName('   ')).toEqual({ ok: false });
+		expect(normalizeSystemName('a'.repeat(SYSTEM_NAME_MAX_LENGTH + 1))).toEqual({ ok: false });
+	});
+
+	it('rejects non-strings', () => {
+		expect(normalizeSystemName(undefined)).toEqual({ ok: false });
+		expect(normalizeSystemName(null)).toEqual({ ok: false });
+		expect(normalizeSystemName(42)).toEqual({ ok: false });
+	});
+});
+
+describe('applySystemName', () => {
+	it('reports unchanged without writing when identical', async () => {
+		const status = await applySystemName(
+			{ id: 'k1', userId: 'u1', systemName: 'Living Room' },
+			'Living Room',
+			'living room'
+		);
+
+		expect(status).toBe('unchanged');
+		expect(keyFindFirst).not.toHaveBeenCalled();
+		expect(keyUpdate).not.toHaveBeenCalled();
+	});
+
+	it('reports conflict when another license on the account holds the name', async () => {
+		keyFindFirst.mockResolvedValue({ id: 'other' });
+
+		const status = await applySystemName(
+			{ id: 'k1', userId: 'u1', systemName: null },
+			'Den',
+			'den'
+		);
+
+		expect(status).toBe('conflict');
+		expect(keyUpdate).not.toHaveBeenCalled();
+	});
+
+	it('writes the name and its case-folded copy when free', async () => {
+		keyFindFirst.mockResolvedValue(null);
+		keyUpdate.mockResolvedValue({});
+
+		const status = await applySystemName(
+			{ id: 'k1', userId: 'u1', systemName: null },
+			'Den',
+			'den'
+		);
+
+		expect(status).toBe('ok');
+		expect(keyUpdate).toHaveBeenCalledWith({
+			where: { id: 'k1' },
+			data: { systemName: 'Den', systemNameLower: 'den' }
+		});
+	});
+
+	it('skips the uniqueness check for a license with no account', async () => {
+		keyUpdate.mockResolvedValue({});
+
+		const status = await applySystemName(
+			{ id: 'k1', userId: null, systemName: null },
+			'Den',
+			'den'
+		);
+
+		expect(status).toBe('ok');
+		expect(keyFindFirst).not.toHaveBeenCalled();
+		expect(keyUpdate).toHaveBeenCalled();
+	});
+
+	it('maps a unique-constraint violation to conflict', async () => {
+		keyFindFirst.mockResolvedValue(null);
+		keyUpdate.mockRejectedValue({ code: 'P2002' });
+
+		const status = await applySystemName(
+			{ id: 'k1', userId: 'u1', systemName: null },
+			'Den',
+			'den'
+		);
+
+		expect(status).toBe('conflict');
+	});
+});
diff --git a/src/lib/server/system-name.ts b/src/lib/server/system-name.ts
new file mode 100644
index 0000000..6c45d9e
--- /dev/null
+++ b/src/lib/server/system-name.ts
@@ -0,0 +1,73 @@
+// System Name helpers. A System Name is a human-readable label for a License
+// Key, set only by the Kiosk and displayed read-only by the Portal. It is never
+// a reference or foreign key. Uniqueness is per account (the owning User) and
+// case-insensitive when non-null, enforced by the unique index on
+// (userId, systemNameLower).
+
+import { prisma } from '$lib/db';
+
+export const SYSTEM_NAME_MAX_LENGTH = 40;
+
+export type SystemNameStatus = 'ok' | 'unchanged' | 'conflict' | 'invalid';
+
+export type NormalizedName = { ok: true; name: string; lower: string } | { ok: false };
+
+/** Trim and validate a caller-supplied System Name. Stored as typed (trimmed);
+ * `lower` is the case-folded copy used for uniqueness. */
+export function normalizeSystemName(raw: unknown): NormalizedName {
+	if (typeof raw !== 'string') return { ok: false };
+	const name = raw.trim();
+	if (name.length < 1 || name.length > SYSTEM_NAME_MAX_LENGTH) return { ok: false };
+	return { ok: true, name, lower: name.toLowerCase() };
+}
+
+type SystemNameLicense = {
+	id: string;
+	userId: string | null;
+	systemName: string | null;
+};
+
+function isUniqueViolation(error: unknown): boolean {
+	return (
+		typeof error === 'object' && error !== null && (error as { code?: string }).code === 'P2002'
+	);
+}
+
+/**
+ * Apply a normalized name to a license. Returns the resulting status:
+ * - `unchanged` when the stored name is already identical
+ * - `conflict` when another license on the same account holds the name
+ * - `ok` when the name was written
+ * A license with no owning account (legacy, userId null) is written without a
+ * uniqueness check; per-account uniqueness cannot apply without an account.
+ */
+export async function applySystemName(
+	license: SystemNameLicense,
+	name: string,
+	lower: string
+): Promise<SystemNameStatus> {
+	if (license.systemName === name) return 'unchanged';
+
+	if (license.userId) {
+		const conflict = await prisma.licenseKey.findFirst({
+			where: {
+				userId: license.userId,
+				systemNameLower: lower,
+				id: { not: license.id }
+			},
+			select: { id: true }
+		});
+		if (conflict) return 'conflict';
+	}
+
+	try {
+		await prisma.licenseKey.update({
+			where: { id: license.id },
+			data: { systemName: name, systemNameLower: lower }
+		});
+		return 'ok';
+	} catch (error) {
+		if (isUniqueViolation(error)) return 'conflict';
+		throw error;
+	}
+}
diff --git a/src/lib/server/v2-serializers.spec.ts b/src/lib/server/v2-serializers.spec.ts
index 2e3a102..0b94e3a 100644
--- a/src/lib/server/v2-serializers.spec.ts
+++ b/src/lib/server/v2-serializers.spec.ts
@@ -139,14 +139,16 @@ describe('serializeGroup', () => {
 });
 
 describe('serializeLicense', () => {
-	it('returns only key and email_address (levels removed)', () => {
+	it('returns key, email_address, and the advisory systemNameStatus', () => {
 		const result = serializeLicense({
 			key: 'XXXX-XXXX-XXXX-XXXX',
-			emailAddress: 'user@example.com'
+			emailAddress: 'user@example.com',
+			systemNameStatus: 'unchanged'
 		});
 		expect(result).toEqual({
 			key: 'XXXX-XXXX-XXXX-XXXX',
-			email_address: 'user@example.com'
+			email_address: 'user@example.com',
+			systemNameStatus: 'unchanged'
 		});
 		expect(Object.keys(result)).not.toContain('subscription_level');
 	});
diff --git a/src/lib/server/v2-serializers.ts b/src/lib/server/v2-serializers.ts
index 5700851..28276f3 100644
--- a/src/lib/server/v2-serializers.ts
+++ b/src/lib/server/v2-serializers.ts
@@ -119,13 +119,20 @@ export function serializeGroup(g: { id: number; name: string; sortOrder: number
 export type V2License = {
 	key: string;
 	email_address: string;
+	systemNameStatus: string;
 };
 
-/** Build the POST /license response. */
-export function serializeLicense(opts: { key: string; emailAddress: string }): V2License {
+/** Build the POST /license response. `systemNameStatus` is advisory: the Kiosk
+ * treats "ok"/"unchanged" as synced and reverts on "conflict"/"invalid". */
+export function serializeLicense(opts: {
+	key: string;
+	emailAddress: string;
+	systemNameStatus: string;
+}): V2License {
 	return {
 		key: opts.key,
-		email_address: opts.emailAddress
+		email_address: opts.emailAddress,
+		systemNameStatus: opts.systemNameStatus
 	};
 }
 
diff --git a/src/routes/api/v2/license/+server.ts b/src/routes/api/v2/license/+server.ts
index b21644f..c7b9acc 100644
--- a/src/routes/api/v2/license/+server.ts
+++ b/src/routes/api/v2/license/+server.ts
@@ -4,6 +4,11 @@ import { prisma } from '$lib/db';
 import { clientIp, jsonOk, rateLimited, readJsonBody } from '$lib/server/v2-helpers';
 import { rateLimit } from '$lib/server/v2-rate-limit';
 import { serializeLicense } from '$lib/server/v2-serializers';
+import {
+	applySystemName,
+	normalizeSystemName,
+	type SystemNameStatus
+} from '$lib/server/system-name';
 
 const LICENSE_KEY_RE = /^[A-Z0-9]{4}-[A-Z0-9]{4}-[A-Z0-9]{4}-[A-Z0-9]{4}$/;
 
@@ -50,6 +55,20 @@ export const POST: RequestHandler = async ({ request }) => {
 		throw error(400, 'key does not belong to specified user');
 	}
 
+	// Optional System Name (Kiosk is the only writer). Validation always
+	// succeeds; a non-ok name status is advisory. An omitted field never
+	// changes or clears the stored name; empty/whitespace is invalid, never a
+	// clear.
+	let systemNameStatus: SystemNameStatus = 'unchanged';
+	if ('systemName' in body) {
+		const parsed = normalizeSystemName(body.systemName);
+		if (!parsed.ok) {
+			systemNameStatus = 'invalid';
+		} else {
+			systemNameStatus = await applySystemName(storedKey, parsed.name, parsed.lower);
+		}
+	}
+
 	// Record that this active key was validated. A failure to record the
 	// timestamp should not fail an otherwise valid validation.
 	try {
@@ -64,7 +83,8 @@ export const POST: RequestHandler = async ({ request }) => {
 	return jsonOk(
 		serializeLicense({
 			key: storedKey.key,
-			emailAddress: email
+			emailAddress: email,
+			systemNameStatus
 		})
 	);
 };
diff --git a/src/routes/api/v2/license/server.spec.ts b/src/routes/api/v2/license/server.spec.ts
index 3fde419..cf63304 100644
--- a/src/routes/api/v2/license/server.spec.ts
+++ b/src/routes/api/v2/license/server.spec.ts
@@ -43,7 +43,8 @@ const storedKey = {
 	id: 'key-1',
 	key: 'ABCD-EFGH-IJKL-MNOP',
 	active: true,
-	userId: 'user-1'
+	userId: 'user-1',
+	systemName: null
 };
 
 describe('POST /api/v2/license', () => {
@@ -64,7 +65,8 @@ describe('POST /api/v2/license', () => {
 		const body = (await res.json()) as Record<string, unknown>;
 		expect(body).toEqual({
 			key: storedKey.key,
-			email_address: 'user@example.com'
+			email_address: 'user@example.com',
+			systemNameStatus: 'unchanged'
 		});
 		expect(Object.keys(body)).not.toContain('subscription_level');
 		expect(mockKeyUpdate).toHaveBeenCalledWith({
@@ -147,3 +149,90 @@ describe('POST /api/v2/license', () => {
 		expect(mockKeyFindFirst).not.toHaveBeenCalled();
 	});
 });
+
+describe('POST /api/v2/license systemName handling', () => {
+	beforeEach(() => {
+		vi.clearAllMocks();
+		_clearRateLimits();
+		mockKeyFindFirst.mockResolvedValue(storedKey);
+		mockUserFindUnique.mockResolvedValue({ id: 'user-1', email: 'user@example.com' });
+		mockKeyUpdate.mockResolvedValue({});
+	});
+
+	async function post(...args: unknown[]) {
+		const body: Record<string, unknown> = {
+			license_key: storedKey.key,
+			email_address: 'user@example.com'
+		};
+		if (args.length > 0) body.systemName = args[0];
+		const res = await POST({ request: licenseRequest(body) } as POSTEvent);
+		return res;
+	}
+
+	it('leaves the name untouched and reports unchanged when omitted', async () => {
+		const res = await post();
+
+		expect((await res.json()).systemNameStatus).toBe('unchanged');
+		expect(mockKeyUpdate).toHaveBeenCalledTimes(1);
+		expect(mockKeyUpdate).toHaveBeenCalledWith({
+			where: { id: storedKey.id },
+			data: { lastValidatedAt: expect.any(Date) }
+		});
+	});
+
+	it('sets a trimmed name, case-folded for uniqueness (ok)', async () => {
+		mockKeyFindFirst.mockResolvedValueOnce(storedKey).mockResolvedValueOnce(null);
+
+		const res = await post('  Living Room  ');
+
+		expect((await res.json()).systemNameStatus).toBe('ok');
+		expect(mockKeyUpdate).toHaveBeenCalledWith({
+			where: { id: storedKey.id },
+			data: { systemName: 'Living Room', systemNameLower: 'living room' }
+		});
+	});
+
+	it('reports conflict without writing when another key holds the name', async () => {
+		mockKeyFindFirst.mockResolvedValueOnce(storedKey).mockResolvedValueOnce({ id: 'other' });
+
+		const res = await post('Living Room');
+
+		expect((await res.json()).systemNameStatus).toBe('conflict');
+		expect(mockKeyUpdate).toHaveBeenCalledTimes(1);
+	});
+
+	it('treats differing casing as a conflict', async () => {
+		mockKeyFindFirst.mockResolvedValueOnce(storedKey).mockResolvedValueOnce({ id: 'other' });
+
+		const res = await post('living room');
+
+		expect((await res.json()).systemNameStatus).toBe('conflict');
+	});
+
+	it('allows the same name in a different account', async () => {
+		mockKeyFindFirst.mockResolvedValueOnce(storedKey).mockResolvedValueOnce(null);
+
+		const res = await post('Living Room');
+
+		expect((await res.json()).systemNameStatus).toBe('ok');
+	});
+
+	it('reports invalid without writing for empty, whitespace, too long, or non-string', async () => {
+		for (const bad of ['', '   ', 'a'.repeat(41), 42]) {
+			const res = await post(bad);
+			expect((await res.json()).systemNameStatus).toBe('invalid');
+		}
+		// Only the lastValidatedAt stamp is written; no name writes.
+		for (const call of mockKeyUpdate.mock.calls) {
+			expect(call[0].data).toEqual({ lastValidatedAt: expect.any(Date) });
+		}
+	});
+
+	it('validation still succeeds (200) on conflict', async () => {
+		mockKeyFindFirst.mockResolvedValueOnce(storedKey).mockResolvedValueOnce({ id: 'other' });
+
+		const res = await post('Living Room');
+
+		expect(res.status).toBe(200);
+	});
+});
diff --git a/src/routes/api/v2/licenses/[licenseKey]/system-name/+server.ts b/src/routes/api/v2/licenses/[licenseKey]/system-name/+server.ts
new file mode 100644
index 0000000..f6cdc46
--- /dev/null
+++ b/src/routes/api/v2/licenses/[licenseKey]/system-name/+server.ts
@@ -0,0 +1,40 @@
+import { error } from '@sveltejs/kit';
+import type { RequestHandler } from './$types';
+import { prisma } from '$lib/db';
+import { clientIp, jsonOk, rateLimited, readJsonBody } from '$lib/server/v2-helpers';
+import { rateLimit } from '$lib/server/v2-rate-limit';
+import { applySystemName, normalizeSystemName } from '$lib/server/system-name';
+
+/**
+ * Kiosk-facing. Sets the System Name for a License Key. The Kiosk is the only
+ * writer; the Portal never calls this. Idempotent: re-sending the current name
+ * returns 200 without a write. Responds 400 `invalid_name`, 404
+ * `unknown_license`, or 409 `name_taken`.
+ */
+export const PUT: RequestHandler = async ({ request, params }) => {
+	const ip = clientIp(request);
+	const rl = rateLimit({ key: `system-name:${ip}`, limit: 10, windowMs: 60_000 });
+	if (!rl.ok) {
+		return rateLimited(rl.retryAfterMs);
+	}
+
+	const licenseKey = (params.licenseKey ?? '').trim();
+	const body = (await readJsonBody(request)) as Record<string, unknown>;
+
+	const parsed = normalizeSystemName(body.systemName);
+	if (!parsed.ok) {
+		throw error(400, 'invalid_name');
+	}
+
+	const license = await prisma.licenseKey.findUnique({ where: { key: licenseKey } });
+	if (!license) {
+		throw error(404, 'unknown_license');
+	}
+
+	const status = await applySystemName(license, parsed.name, parsed.lower);
+	if (status === 'conflict') {
+		throw error(409, 'name_taken');
+	}
+
+	return jsonOk({ systemName: parsed.name, systemNameStatus: 'ok' });
+};
diff --git a/src/routes/api/v2/licenses/[licenseKey]/system-name/server.spec.ts b/src/routes/api/v2/licenses/[licenseKey]/system-name/server.spec.ts
new file mode 100644
index 0000000..d2949fe
--- /dev/null
+++ b/src/routes/api/v2/licenses/[licenseKey]/system-name/server.spec.ts
@@ -0,0 +1,108 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { isHttpError } from '@sveltejs/kit';
+import { _clearRateLimits } from '$lib/server/v2-rate-limit';
+
+vi.mock('$lib/db', () => ({
+	prisma: {
+		licenseKey: { findUnique: vi.fn(), findFirst: vi.fn(), update: vi.fn() }
+	}
+}));
+
+import { prisma } from '$lib/db';
+import { PUT } from './+server';
+
+type PUTEvent = Parameters<typeof PUT>[0];
+
+const mockFindUnique = prisma.licenseKey.findUnique as ReturnType<typeof vi.fn>;
+const mockFindFirst = prisma.licenseKey.findFirst as ReturnType<typeof vi.fn>;
+const mockUpdate = prisma.licenseKey.update as ReturnType<typeof vi.fn>;
+
+const KEY = 'ABCD-EFGH-IJKL-MNOP';
+
+const storedKey = {
+	id: 'key-1',
+	key: KEY,
+	active: true,
+	userId: 'user-1',
+	systemName: null as string | null
+};
+
+function putRequest(body: unknown): Request {
+	return new Request(`http://localhost/api/v2/licenses/${KEY}/system-name`, {
+		method: 'PUT',
+		headers: { 'content-type': 'application/json' },
+		body: JSON.stringify(body)
+	});
+}
+
+function event(body: unknown): PUTEvent {
+	return { request: putRequest(body), params: { licenseKey: KEY } } as PUTEvent;
+}
+
+async function expectHttpError(promise: unknown, status: number, message: string) {
+	try {
+		await promise;
+	} catch (e) {
+		expect(isHttpError(e)).toBe(true);
+		const err = e as { status: number; body: { message: string } };
+		expect(err.status).toBe(status);
+		expect(err.body.message).toBe(message);
+		return;
+	}
+	throw new Error('expected handler to throw an HttpError');
+}
+
+beforeEach(() => {
+	vi.clearAllMocks();
+	_clearRateLimits();
+});
+
+describe('PUT /api/v2/licenses/[licenseKey]/system-name', () => {
+	it('sets the name and returns it', async () => {
+		mockFindUnique.mockResolvedValue(storedKey);
+		mockFindFirst.mockResolvedValue(null);
+		mockUpdate.mockResolvedValue({});
+
+		const res = await PUT(event({ systemName: '  Living Room  ' }));
+
+		expect(res.status).toBe(200);
+		expect(await res.json()).toEqual({ systemName: 'Living Room', systemNameStatus: 'ok' });
+		expect(mockUpdate).toHaveBeenCalledWith({
+			where: { id: 'key-1' },
+			data: { systemName: 'Living Room', systemNameLower: 'living room' }
+		});
+	});
+
+	it('is idempotent when the name is unchanged', async () => {
+		mockFindUnique.mockResolvedValue({ ...storedKey, systemName: 'Living Room' });
+
+		const res = await PUT(event({ systemName: 'Living Room' }));
+
+		expect(res.status).toBe(200);
+		expect(await res.json()).toEqual({ systemName: 'Living Room', systemNameStatus: 'ok' });
+		expect(mockUpdate).not.toHaveBeenCalled();
+	});
+
+	it('rejects an invalid name', async () => {
+		await expectHttpError(PUT(event({ systemName: '   ' })), 400, 'invalid_name');
+		await expectHttpError(PUT(event({ systemName: '' })), 400, 'invalid_name');
+		await expectHttpError(PUT(event({ systemName: 'a'.repeat(41) })), 400, 'invalid_name');
+		await expectHttpError(PUT(event({})), 400, 'invalid_name');
+		expect(mockFindUnique).not.toHaveBeenCalled();
+	});
+
+	it('returns 404 for an unknown license', async () => {
+		mockFindUnique.mockResolvedValue(null);
+
+		await expectHttpError(PUT(event({ systemName: 'Den' })), 404, 'unknown_license');
+		expect(mockUpdate).not.toHaveBeenCalled();
+	});
+
+	it('returns 409 when another license on the account holds the name', async () => {
+		mockFindUnique.mockResolvedValue(storedKey);
+		mockFindFirst.mockResolvedValue({ id: 'other' });
+
+		await expectHttpError(PUT(event({ systemName: 'Den' })), 409, 'name_taken');
+		expect(mockUpdate).not.toHaveBeenCalled();
+	});
+});