diff --git a/frontend/src/lib/api.ts b/frontend/src/lib/api.ts
index 528ac63..bd58112 100644
--- a/frontend/src/lib/api.ts
+++ b/frontend/src/lib/api.ts
@@ -5,10 +5,23 @@ import type {
   QuestionDetail,
   QuestionListResponse,
   Stats,
+  SubmissionRequest,
+  SubmissionResponse,
 } from "@/types";
 
 const API_BASE_URL = process.env.NEXT_PUBLIC_API_URL || "http://localhost:8000";
 
+export class ApiError extends Error {
+  constructor(
+    public status: number,
+    public statusText: string,
+    public detail?: string
+  ) {
+    super(detail || `API error: ${status} ${statusText}`);
+    this.name = "ApiError";
+  }
+}
+
 async function fetchApi<T>(
   endpoint: string,
   options?: RequestInit
@@ -23,7 +36,14 @@ async function fetchApi<T>(
   });
 
   if (!response.ok) {
-    throw new Error(`API error: ${response.status} ${response.statusText}`);
+    let detail: string | undefined;
+    try {
+      const errorBody = await response.json();
+      detail = errorBody.detail;
+    } catch {
+      // Ignore JSON parse errors
+    }
+    throw new ApiError(response.status, response.statusText, detail);
   }
 
   return response.json();
@@ -77,3 +97,13 @@ export async function getPattern(slug: string): Promise<Pattern> {
 export async function getStats(): Promise<Stats> {
   return fetchApi<Stats>("/api/stats");
 }
+
+export async function submitSolution(
+  slug: string,
+  submission: SubmissionRequest
+): Promise<SubmissionResponse> {
+  return fetchApi<SubmissionResponse>(`/api/questions/${slug}/submit`, {
+    method: "POST",
+    body: JSON.stringify(submission),
+  });
+}
diff --git a/frontend/src/types/index.ts b/frontend/src/types/index.ts
index 444bb90..322d94f 100644
--- a/frontend/src/types/index.ts
+++ b/frontend/src/types/index.ts
@@ -61,6 +61,17 @@ export interface Solution {
   explanation: string | null;
 }
 
+export interface VisibleTestCase {
+  id: number;
+  input: Record<string, unknown>;
+  expected: unknown;
+}
+
+export interface HiddenTestInput {
+  id: number;
+  input: Record<string, unknown>;
+}
+
 export interface QuestionDetail extends QuestionListItem {
   description: string;
   constraints: string | null;
@@ -69,6 +80,9 @@ export interface QuestionDetail extends QuestionListItem {
     output: string;
     explanation?: string;
   }> | null;
+  function_signature: string | null;
+  visible_test_cases: VisibleTestCase[] | null;
+  hidden_test_inputs: HiddenTestInput[] | null;
   explanation: Explanation | null;
   solutions: Solution[];
   updated_at: string;
@@ -114,3 +128,30 @@ export interface Stats {
   by_category: CategoryCount[];
   by_pattern: PatternCount[];
 }
+
+export interface HiddenTestOutput {
+  test_id: number;
+  output: unknown;
+}
+
+export interface SubmissionRequest {
+  code: string;
+  hidden_outputs: HiddenTestOutput[];
+}
+
+export interface TestResult {
+  test_id: number;
+  passed: boolean;
+  input?: Record<string, unknown>;
+  expected?: unknown;
+  actual: unknown;
+  error?: string;
+}
+
+export interface SubmissionResponse {
+  passed: boolean;
+  visible_results: TestResult[];
+  hidden_results: TestResult[];
+  total_passed: number;
+  total_tests: number;
+}