diff --git a/src/commands/new.ts b/src/commands/new.ts
index 5406dda..7181a93 100644
--- a/src/commands/new.ts
+++ b/src/commands/new.ts
@@ -1,10 +1,11 @@
 import { Command } from 'commander';
-import { InternalCliError, ValidationCliError } from '../errors/errors.js';
+import { InternalCliError } from '../errors/errors.js';
 import { orchestrateProjectGeneration } from '../generator/orchestrator.js';
-import type {
-  ProjectGeneratorServices,
-  ValidatedProjectInput,
-} from '../generator/types.js';
+import type { ProjectGeneratorServices } from '../generator/types.js';
+import {
+  planProjectDestination,
+  validateProjectInput,
+} from '../generator/validation.js';
 import { TerminalOutput } from '../output/terminal.js';
 
 export interface NewCommandOptions {
@@ -15,23 +16,8 @@ export interface NewCommandOptions {
 
 function createScaffoldServices(): ProjectGeneratorServices {
   return {
-    validate(input): ValidatedProjectInput {
-      const projectName = input.projectName.trim();
-
-      if (projectName.length === 0) {
-        throw new ValidationCliError('Project name must not be empty.');
-      }
-
-      return {
-        projectName,
-        cwd: input.cwd,
-      };
-    },
-    planDestination() {
-      throw new InternalCliError({
-        cause: new Error('Destination planning is not implemented yet.'),
-      });
-    },
+    validate: validateProjectInput,
+    planDestination: planProjectDestination,
     selectTemplate() {
       throw new InternalCliError({
         cause: new Error('Template selection is not implemented yet.'),
diff --git a/src/generator/validation.ts b/src/generator/validation.ts
new file mode 100644
index 0000000..83b1790
--- /dev/null
+++ b/src/generator/validation.ts
@@ -0,0 +1,127 @@
+import { existsSync, readdirSync, statSync } from 'node:fs';
+import { isAbsolute, relative, resolve } from 'node:path';
+import { ValidationCliError } from '../errors/errors.js';
+import type {
+  DestinationPlan,
+  ProjectGeneratorInput,
+  ValidatedProjectInput,
+} from './types.js';
+
+const WINDOWS_RESERVED_NAME = /^(con|prn|aux|nul|com[1-9]|lpt[1-9])(?:\..*)?$/i;
+const SAFE_PROJECT_NAME = /^[A-Za-z0-9][A-Za-z0-9._-]*$/;
+
+export interface DestinationFileSystem {
+  exists(path: string): boolean;
+  isDirectory(path: string): boolean;
+  entries(path: string): readonly string[];
+}
+
+const nodeFileSystem: DestinationFileSystem = {
+  exists: existsSync,
+  isDirectory(path) {
+    return statSync(path).isDirectory();
+  },
+  entries: readdirSync,
+};
+
+function validateProjectName(projectName: string): string {
+  const normalized = projectName.trim();
+
+  if (normalized.length === 0) {
+    throw new ValidationCliError('Project name must not be empty.');
+  }
+
+  if (normalized === '.' || normalized === '..') {
+    throw new ValidationCliError(
+      'Project name must identify a new child directory, not `.` or `..`.',
+    );
+  }
+
+  if (
+    isAbsolute(normalized) ||
+    normalized.includes('/') ||
+    normalized.includes('\\')
+  ) {
+    throw new ValidationCliError(
+      'Project name must be a single directory name and must not contain a path.',
+    );
+  }
+
+  if (!SAFE_PROJECT_NAME.test(normalized)) {
+    throw new ValidationCliError(
+      'Project name may contain only letters, numbers, dots, underscores, and hyphens, and must start with a letter or number.',
+    );
+  }
+
+  if (normalized.endsWith('.') || normalized.endsWith(' ')) {
+    throw new ValidationCliError(
+      'Project name must not end with a dot or space.',
+    );
+  }
+
+  if (WINDOWS_RESERVED_NAME.test(normalized)) {
+    throw new ValidationCliError(
+      'Project name conflicts with a reserved Windows device name.',
+    );
+  }
+
+  return normalized;
+}
+
+export function validateProjectInput(
+  input: ProjectGeneratorInput,
+): ValidatedProjectInput {
+  const projectName = validateProjectName(input.projectName);
+  const cwd = resolve(input.cwd);
+
+  return {
+    projectName,
+    cwd,
+  };
+}
+
+function assertDestinationWithinRoot(root: string, destination: string): void {
+  const relativeDestination = relative(root, destination);
+
+  if (
+    relativeDestination.length === 0 ||
+    relativeDestination === '..' ||
+    relativeDestination.startsWith(
+      `..${process.platform === 'win32' ? '\\' : '/'}`,
+    ) ||
+    isAbsolute(relativeDestination)
+  ) {
+    throw new ValidationCliError(
+      'Project destination must remain inside the current working directory.',
+    );
+  }
+}
+
+export function planProjectDestination(
+  input: ValidatedProjectInput,
+  fileSystem: DestinationFileSystem = nodeFileSystem,
+): DestinationPlan {
+  const root = resolve(input.cwd);
+  const destination = resolve(root, input.projectName);
+
+  assertDestinationWithinRoot(root, destination);
+
+  if (fileSystem.exists(destination)) {
+    if (!fileSystem.isDirectory(destination)) {
+      throw new ValidationCliError(
+        `Destination already exists and is not a directory: ${destination}`,
+      );
+    }
+
+    if (fileSystem.entries(destination).length > 0) {
+      throw new ValidationCliError(
+        `Destination directory is not empty: ${destination}. StellarForge will not overwrite existing files.`,
+      );
+    }
+  }
+
+  return {
+    projectName: input.projectName,
+    destination,
+  };
+}
diff --git a/tests/project-validation.test.ts b/tests/project-validation.test.ts
new file mode 100644
index 0000000..02c05e8
--- /dev/null
+++ b/tests/project-validation.test.ts
@@ -0,0 +1,102 @@
+import { mkdirSync, writeFileSync } from 'node:fs';
+import { join, resolve } from 'node:path';
+import { describe, expect, it } from 'vitest';
+import { ValidationCliError } from '../src/errors/errors.js';
+import {
+  planProjectDestination,
+  validateProjectInput,
+} from '../src/generator/validation.js';
+import { withTempDirectory } from './helpers/index.js';
+
+describe('project input validation', () => {
+  it.each([
+    '../escape',
+    '..\\escape',
+    '/tmp/escape',
+    'C:\\temp\\escape',
+    'C:/temp/escape',
+    '.',
+    '..',
+    '.hidden',
+    'nested/project',
+    'nested\\project',
+  ])('rejects path-like or traversal project name %j', (projectName) => {
+    expect(() =>
+      validateProjectInput({ projectName, cwd: '/workspace' }),
+    ).toThrow(ValidationCliError);
+  });
+
+  it.each(['CON', 'prn', 'AUX.txt', 'COM1', 'lpt9.log'])(
+    'rejects Windows reserved device name %j',
+    (projectName) => {
+      expect(() =>
+        validateProjectInput({ projectName, cwd: '/workspace' }),
+      ).toThrow('reserved Windows device name');
+    },
+  );
+
+  it.each(['demo', 'demo-app', 'demo_app', 'demo.app', 'Demo123'])(
+    'accepts safe single-segment project name %j',
+    (projectName) => {
+      const validated = validateProjectInput({
+        projectName,
+        cwd: './workspace/..',
+      });
+
+      expect(validated.projectName).toBe(projectName);
+      expect(validated.cwd).toBe(resolve('./workspace/..'));
+    },
+  );
+});
+
+describe('project destination planning', () => {
+  it('plans a direct child without creating it', () =>
+    withTempDirectory((path) => {
+      const validated = validateProjectInput({
+        projectName: 'demo',
+        cwd: path,
+      });
+      const plan = planProjectDestination(validated);
+
+      expect(plan).toEqual({
+        projectName: 'demo',
+        destination: join(path, 'demo'),
+      });
+    }));
+
+  it('allows an existing empty destination directory', () =>
+    withTempDirectory((path) => {
+      const destination = join(path, 'demo');
+      mkdirSync(destination);
+
+      const plan = planProjectDestination(
+        validateProjectInput({ projectName: 'demo', cwd: path }),
+      );
+
+      expect(plan.destination).toBe(destination);
+    }));
+
+  it('refuses an existing non-empty destination directory', () =>
+    withTempDirectory((path) => {
+      const destination = join(path, 'demo');
+      mkdirSync(destination);
+      writeFileSync(join(destination, 'existing.txt'), 'do not overwrite');
+
+      expect(() =>
+        planProjectDestination(
+          validateProjectInput({ projectName: 'demo', cwd: path }),
+        ),
+      ).toThrow('will not overwrite existing files');
+    }));
+
+  it('refuses a destination occupied by a file', () =>
+    withTempDirectory((path) => {
+      writeFileSync(join(path, 'demo'), 'existing file');
+
+      expect(() =>
+        planProjectDestination(
+          validateProjectInput({ projectName: 'demo', cwd: path }),
+        ),
+      ).toThrow('is not a directory');
+    }));
+});