diff --git a/packages/shared/src/__tests__/platforms.test.ts b/packages/shared/src/__tests__/platforms.test.ts
new file mode 100644
index 00000000..baca6e5e
--- /dev/null
+++ b/packages/shared/src/__tests__/platforms.test.ts
@@ -0,0 +1,24 @@
+import { describe, it, expect } from 'vitest';
+import { isSupportedPlatform, PLATFORMS } from '../platforms';
+
+// ─── isSupportedPlatform Tests ───
+
+describe('isSupportedPlatform', () => {
+  it('should return true for every registered platform', () => {
+    for (const id of Object.keys(PLATFORMS)) {
+      expect(isSupportedPlatform(id)).toBe(true);
+    }
+  });
+
+  it('should return false for an unknown platform ID', () => {
+    expect(isSupportedPlatform('nonexistent')).toBe(false);
+  });
+
+  it('should return false for an empty string', () => {
+    expect(isSupportedPlatform('')).toBe(false);
+  });
+
+  it('should return false for different casing', () => {
+    expect(isSupportedPlatform('Github')).toBe(false);
+  });
+});
diff --git a/packages/shared/src/platforms.ts b/packages/shared/src/platforms.ts
index 81c81ab4..9c36173b 100644
--- a/packages/shared/src/platforms.ts
+++ b/packages/shared/src/platforms.ts
@@ -272,6 +272,11 @@ export function getPlatform(id: string): PlatformDef | undefined {
   return PLATFORMS[id];
 }
 
+/** Check whether a platform ID exists in the registry */
+export function isSupportedPlatform(id: string): boolean {
+  return Object.prototype.hasOwnProperty.call(PLATFORMS, id);
+}
+
 /** Get the profile URL for a given platform and username */
 export function getProfileUrl(platformId: string, username: string): string {
   const platform = PLATFORMS[platformId];
diff --git a/packages/shared/tsconfig.json b/packages/shared/tsconfig.json
index 771659c0..1397cd1f 100644
--- a/packages/shared/tsconfig.json
+++ b/packages/shared/tsconfig.json
@@ -9,7 +9,8 @@
     "forceConsistentCasingInFileNames": true,
     "declaration": true,
     "outDir": "./dist",
-    "rootDir": "./src"
+    "rootDir": "./src",
+    "types": ["vitest/globals"]
   },
   "include": ["src/**/*"]
 }