diff --git a/packages/create-void/src/args.ts b/packages/create-void/src/args.ts
index 07e4f404a..e1e8b50be 100644
--- a/packages/create-void/src/args.ts
+++ b/packages/create-void/src/args.ts
@@ -7,10 +7,24 @@ export type CreateArgs = {
 // `--framework react` or `--deploy=none` to `void init`.
 const INIT_ARG_PATTERN = /^[\w=-]+$/;
 
+export function validateProjectName(value: string | undefined): string | undefined {
+  if (value && !value.trim()) {
+    return 'Project name cannot be blank';
+  }
+  if (value !== undefined && value !== value.toLowerCase()) {
+    return 'Project name must be lowercase';
+  }
+  return undefined;
+}
+
 /** Split `create-void [name] [void init options]` into the name and the options. */
 export function parseCreateArgs(argv: ReadonlyArray<string>): CreateArgs {
   const [first, ...rest] = argv;
   const appName = first !== undefined && !first.startsWith('-') ? first : undefined;
+  const nameError = validateProjectName(appName);
+  if (nameError) {
+    throw new Error(`create-void: ${nameError}`);
+  }
   const initArgs = appName === undefined ? [...argv] : rest;
   for (const arg of initArgs) {
     if (!INIT_ARG_PATTERN.test(arg)) {
diff --git a/packages/create-void/src/index.ts b/packages/create-void/src/index.ts
index 8e49a8013..4aaefae26 100644
--- a/packages/create-void/src/index.ts
+++ b/packages/create-void/src/index.ts
@@ -4,7 +4,7 @@ import { existsSync, mkdirSync, readdirSync, readFileSync, writeFileSync } from
 import * as p from '@voidzero-dev/vite-plus-prompts';
 import { resolve } from 'pathslash';
 import pc from 'picocolors';
-import { parseCreateArgs } from './args.ts';
+import { parseCreateArgs, validateProjectName } from './args.ts';
 import { detectPM, pmExec, pmInstall, run, writePnpmBuildPolicy } from './pm.ts';
 
 const pm = detectPM();
@@ -25,11 +25,7 @@ async function main() {
       message: 'Project name:',
       defaultValue: 'my-app',
       placeholder: 'my-app',
-      validate(value) {
-        if (value && !value.trim()) {
-          return 'Project name cannot be blank';
-        }
-      },
+      validate: validateProjectName,
     });
     if (p.isCancel(name) || typeof name !== 'string') {
       p.cancel('Cancelled.');
diff --git a/packages/create-void/test/unit/args.test.ts b/packages/create-void/test/unit/args.test.ts
index 86f799c59..9795a39ff 100644
--- a/packages/create-void/test/unit/args.test.ts
+++ b/packages/create-void/test/unit/args.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vite-plus/test';
-import { parseCreateArgs } from '../../src/args.ts';
+import { parseCreateArgs, validateProjectName } from '../../src/args.ts';
 
 describe('parseCreateArgs', () => {
   it('forwards options after the project name to void init', () => {
@@ -17,9 +17,29 @@ describe('parseCreateArgs', () => {
     expect(parseCreateArgs([])).toEqual({ appName: undefined, initArgs: [] });
   });
 
+  it.each(['MyApp', 'my-App', 'MY-APP'])('rejects an uppercase project name: %s', (name) => {
+    expect(() => parseCreateArgs([name])).toThrow('create-void: Project name must be lowercase');
+  });
+
   it('rejects arguments that are not plain flags or values', () => {
     expect(() => parseCreateArgs(['my-app', '--framework', 'react&calc'])).toThrow(
       "create-void: Unsupported argument 'react&calc'.",
     );
   });
 });
+
+describe('validateProjectName', () => {
+  it.each(['MyApp', 'my-App', 'MY-APP'])('rejects uppercase names: %s', (name) => {
+    expect(validateProjectName(name)).toBe('Project name must be lowercase');
+  });
+
+  it.each(['my-app', 'app123', 'nested/my-app', '.'])('accepts lowercase names: %s', (name) => {
+    expect(validateProjectName(name)).toBeUndefined();
+  });
+
+  it('allows the prompt default and rejects whitespace-only names', () => {
+    expect(validateProjectName(undefined)).toBeUndefined();
+    expect(validateProjectName('')).toBeUndefined();
+    expect(validateProjectName('   ')).toBe('Project name cannot be blank');
+  });
+});