diff --git a/packages/shared/src/__tests__/platforms.test.ts b/packages/shared/src/__tests__/platforms.test.ts
new file mode 100644
index 0000000..dace5a0
--- /dev/null
+++ b/packages/shared/src/__tests__/platforms.test.ts
@@ -0,0 +1,45 @@
+import { describe, it, expect } from 'vitest';
+import { isSupportedPlatform } from '../platforms';
+
+// ─── isSupportedPlatform Tests ───
+
+describe('isSupportedPlatform', () => {
+  it('returns true for known platform: github', () => {
+    expect(isSupportedPlatform('github')).toBe(true);
+  });
+
+  it('returns true for known platform: linkedin', () => {
+    expect(isSupportedPlatform('linkedin')).toBe(true);
+  });
+
+  it('returns true for known platform: twitter', () => {
+    expect(isSupportedPlatform('twitter')).toBe(true);
+  });
+
+  it('returns true for known platform: discord', () => {
+    expect(isSupportedPlatform('discord')).toBe(true);
+  });
+
+  it('returns true for known platform: email', () => {
+    expect(isSupportedPlatform('email')).toBe(true);
+  });
+
+  it('returns false for unknown platform id', () => {
+    expect(isSupportedPlatform('unknown-platform')).toBe(false);
+  });
+
+  it('returns false for empty string', () => {
+    expect(isSupportedPlatform('')).toBe(false);
+  });
+
+  it('returns false for near-miss platform names', () => {
+    expect(isSupportedPlatform('Github')).toBe(false);
+    expect(isSupportedPlatform('GITHUB')).toBe(false);
+    expect(isSupportedPlatform('git hub')).toBe(false);
+  });
+
+  it('returns a boolean value (not truthy/falsy)', () => {
+    expect(typeof isSupportedPlatform('github')).toBe('boolean');
+    expect(typeof isSupportedPlatform('nope')).toBe('boolean');
+  });
+});
diff --git a/packages/shared/src/platforms.ts b/packages/shared/src/platforms.ts
index 81c81ab..aa7ce0b 100644
--- a/packages/shared/src/platforms.ts
+++ b/packages/shared/src/platforms.ts
@@ -292,3 +292,8 @@ export function getDeepLinkUrl(platformId: string, username: string): string | n
   if (!platform?.deepLinkPattern) return null;
   return platform.deepLinkPattern.replace(/{username}/g, username);
 }
+
+/** Returns true if the given ID corresponds to a known platform */
+export function isSupportedPlatform(id: string): boolean {
+  return PLATFORMS[id] !== undefined;
+}