diff --git a/app/api/sandboxes/setup/route.ts b/app/api/sandboxes/setup/route.ts
new file mode 100644
index 00000000..8ee33199
--- /dev/null
+++ b/app/api/sandboxes/setup/route.ts
@@ -0,0 +1,45 @@
+import type { NextRequest } from "next/server";
+import { NextResponse } from "next/server";
+import { getCorsHeaders } from "@/lib/networking/getCorsHeaders";
+import { setupSandboxHandler } from "@/lib/sandbox/setupSandboxHandler";
+
+/**
+ * OPTIONS handler for CORS preflight requests.
+ *
+ * @returns A NextResponse with CORS headers.
+ */
+export async function OPTIONS() {
+  return new NextResponse(null, {
+    status: 200,
+    headers: getCorsHeaders(),
+  });
+}
+
+/**
+ * POST /api/sandboxes/setup
+ *
+ * Triggers the setup-sandbox background task to create a personal sandbox,
+ * provision a GitHub repo, take a snapshot, and shut down.
+ * For personal API keys, sets up the sandbox for the key owner's account.
+ * Organization API keys may specify account_id to target any account
+ * within their organization.
+ *
+ * Authentication: x-api-key header or Authorization Bearer token required.
+ *
+ * Request body:
+ * - account_id: string (optional) - UUID of the account to set up for (org keys only)
+ *
+ * Response (200):
+ * - status: "success"
+ * - runId: string - The Trigger.dev run ID for the background task
+ *
+ * Error (400/401/500):
+ * - status: "error"
+ * - error: string
+ *
+ * @param request - The request object
+ * @returns A NextResponse with the setup result or error
+ */
+export async function POST(request: NextRequest): Promise<Response> {
+  return setupSandboxHandler(request);
+}
diff --git a/lib/sandbox/__tests__/setupSandboxHandler.test.ts b/lib/sandbox/__tests__/setupSandboxHandler.test.ts
new file mode 100644
index 00000000..5f21a7cd
--- /dev/null
+++ b/lib/sandbox/__tests__/setupSandboxHandler.test.ts
@@ -0,0 +1,79 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest, NextResponse } from "next/server";
+import { setupSandboxHandler } from "@/lib/sandbox/setupSandboxHandler";
+
+import { validateSetupSandboxBody } from "@/lib/sandbox/validateSetupSandboxBody";
+import { triggerSetupSandbox } from "@/lib/trigger/triggerSetupSandbox";
+
+vi.mock("@/lib/networking/getCorsHeaders", () => ({
+  getCorsHeaders: vi.fn(() => ({ "Access-Control-Allow-Origin": "*" })),
+}));
+
+vi.mock("@/lib/sandbox/validateSetupSandboxBody", () => ({
+  validateSetupSandboxBody: vi.fn(),
+}));
+
+vi.mock("@/lib/trigger/triggerSetupSandbox", () => ({
+  triggerSetupSandbox: vi.fn(),
+}));
+
+describe("setupSandboxHandler", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("returns validation error when validation fails", async () => {
+    const errorResponse = NextResponse.json(
+      { status: "error", error: "Unauthorized" },
+      { status: 401 },
+    );
+    vi.mocked(validateSetupSandboxBody).mockResolvedValue(errorResponse);
+
+    const request = new NextRequest("http://localhost/api/sandboxes/setup", {
+      method: "POST",
+    });
+
+    const result = await setupSandboxHandler(request);
+
+    expect(result).toBe(errorResponse);
+  });
+
+  it("returns success with runId when trigger succeeds", async () => {
+    vi.mocked(validateSetupSandboxBody).mockResolvedValue({
+      accountId: "test-account-id",
+    });
+    vi.mocked(triggerSetupSandbox).mockResolvedValue({
+      id: "run_abc123",
+    } as never);
+
+    const request = new NextRequest("http://localhost/api/sandboxes/setup", {
+      method: "POST",
+    });
+
+    const result = await setupSandboxHandler(request);
+    const body = await result.json();
+
+    expect(result.status).toBe(200);
+    expect(body).toEqual({ status: "success", runId: "run_abc123" });
+  });
+
+  it("returns error when trigger fails", async () => {
+    vi.mocked(validateSetupSandboxBody).mockResolvedValue({
+      accountId: "test-account-id",
+    });
+    vi.mocked(triggerSetupSandbox).mockRejectedValue(new Error("Trigger.dev connection failed"));
+
+    const request = new NextRequest("http://localhost/api/sandboxes/setup", {
+      method: "POST",
+    });
+
+    const result = await setupSandboxHandler(request);
+    const body = await result.json();
+
+    expect(result.status).toBe(500);
+    expect(body).toEqual({
+      status: "error",
+      error: "Trigger.dev connection failed",
+    });
+  });
+});
diff --git a/lib/sandbox/__tests__/validateSetupSandboxBody.test.ts b/lib/sandbox/__tests__/validateSetupSandboxBody.test.ts
new file mode 100644
index 00000000..5a6ab035
--- /dev/null
+++ b/lib/sandbox/__tests__/validateSetupSandboxBody.test.ts
@@ -0,0 +1,117 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest, NextResponse } from "next/server";
+import { validateSetupSandboxBody } from "@/lib/sandbox/validateSetupSandboxBody";
+
+import { validateAuthContext } from "@/lib/auth/validateAuthContext";
+import { safeParseJson } from "@/lib/networking/safeParseJson";
+
+vi.mock("@/lib/networking/getCorsHeaders", () => ({
+  getCorsHeaders: vi.fn(() => ({ "Access-Control-Allow-Origin": "*" })),
+}));
+
+vi.mock("@/lib/auth/validateAuthContext", () => ({
+  validateAuthContext: vi.fn(),
+}));
+
+vi.mock("@/lib/networking/safeParseJson", () => ({
+  safeParseJson: vi.fn(),
+}));
+
+describe("validateSetupSandboxBody", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("returns 401 when auth fails", async () => {
+    const authError = NextResponse.json(
+      { status: "error", error: "Unauthorized" },
+      { status: 401 },
+    );
+    vi.mocked(safeParseJson).mockResolvedValue({});
+    vi.mocked(validateAuthContext).mockResolvedValue(authError);
+
+    const request = new NextRequest("http://localhost/api/sandboxes/setup", {
+      method: "POST",
+    });
+
+    const result = await validateSetupSandboxBody(request);
+
+    expect(result).toBeInstanceOf(NextResponse);
+    expect((result as NextResponse).status).toBe(401);
+  });
+
+  it("returns 400 when account_id is not a valid UUID", async () => {
+    vi.mocked(safeParseJson).mockResolvedValue({
+      account_id: "not-a-uuid",
+    });
+
+    const request = new NextRequest("http://localhost/api/sandboxes/setup", {
+      method: "POST",
+    });
+
+    const result = await validateSetupSandboxBody(request);
+
+    expect(result).toBeInstanceOf(NextResponse);
+    expect((result as NextResponse).status).toBe(400);
+  });
+
+  it("returns validated accountId on success with no body", async () => {
+    vi.mocked(safeParseJson).mockResolvedValue({});
+    vi.mocked(validateAuthContext).mockResolvedValue({
+      accountId: "resolved-account-id",
+      orgId: null,
+      authToken: "test-token",
+    });
+
+    const request = new NextRequest("http://localhost/api/sandboxes/setup", {
+      method: "POST",
+    });
+
+    const result = await validateSetupSandboxBody(request);
+
+    expect(result).not.toBeInstanceOf(NextResponse);
+    expect(result).toEqual({ accountId: "resolved-account-id" });
+  });
+
+  it("passes account_id override to validateAuthContext for org keys", async () => {
+    const targetAccountId = "550e8400-e29b-41d4-a716-446655440000";
+    vi.mocked(safeParseJson).mockResolvedValue({
+      account_id: targetAccountId,
+    });
+    vi.mocked(validateAuthContext).mockResolvedValue({
+      accountId: targetAccountId,
+      orgId: "org-123",
+      authToken: "test-token",
+    });
+
+    const request = new NextRequest("http://localhost/api/sandboxes/setup", {
+      method: "POST",
+    });
+
+    const result = await validateSetupSandboxBody(request);
+
+    expect(validateAuthContext).toHaveBeenCalledWith(request, {
+      accountId: targetAccountId,
+    });
+    expect(result).toEqual({ accountId: targetAccountId });
+  });
+
+  it("calls validateAuthContext with no accountId when body is empty", async () => {
+    vi.mocked(safeParseJson).mockResolvedValue({});
+    vi.mocked(validateAuthContext).mockResolvedValue({
+      accountId: "default-account-id",
+      orgId: null,
+      authToken: "test-token",
+    });
+
+    const request = new NextRequest("http://localhost/api/sandboxes/setup", {
+      method: "POST",
+    });
+
+    await validateSetupSandboxBody(request);
+
+    expect(validateAuthContext).toHaveBeenCalledWith(request, {
+      accountId: undefined,
+    });
+  });
+});
diff --git a/lib/sandbox/setupSandboxHandler.ts b/lib/sandbox/setupSandboxHandler.ts
new file mode 100644
index 00000000..4beccd73
--- /dev/null
+++ b/lib/sandbox/setupSandboxHandler.ts
@@ -0,0 +1,37 @@
+import type { NextRequest } from "next/server";
+import { NextResponse } from "next/server";
+import { getCorsHeaders } from "@/lib/networking/getCorsHeaders";
+import { validateSetupSandboxBody } from "@/lib/sandbox/validateSetupSandboxBody";
+import { triggerSetupSandbox } from "@/lib/trigger/triggerSetupSandbox";
+
+/**
+ * Handler for POST /api/sandboxes/setup.
+ *
+ * Triggers the setup-sandbox background task to create a personal sandbox,
+ * provision a GitHub repo, take a snapshot, and shut down.
+ * Requires authentication via x-api-key header or Authorization Bearer token.
+ *
+ * @param request - The request object
+ * @returns A NextResponse with the trigger result or error
+ */
+export async function setupSandboxHandler(request: NextRequest): Promise<NextResponse> {
+  const validated = await validateSetupSandboxBody(request);
+  if (validated instanceof NextResponse) {
+    return validated;
+  }
+
+  try {
+    const handle = await triggerSetupSandbox(validated.accountId);
+
+    return NextResponse.json(
+      { status: "success", runId: handle.id },
+      { status: 200, headers: getCorsHeaders() },
+    );
+  } catch (error) {
+    const message = error instanceof Error ? error.message : "Failed to trigger setup-sandbox";
+    return NextResponse.json(
+      { status: "error", error: message },
+      { status: 500, headers: getCorsHeaders() },
+    );
+  }
+}
diff --git a/lib/sandbox/validateSetupSandboxBody.ts b/lib/sandbox/validateSetupSandboxBody.ts
new file mode 100644
index 00000000..15ee78ab
--- /dev/null
+++ b/lib/sandbox/validateSetupSandboxBody.ts
@@ -0,0 +1,58 @@
+import type { NextRequest } from "next/server";
+import { NextResponse } from "next/server";
+import { getCorsHeaders } from "@/lib/networking/getCorsHeaders";
+import { validateAuthContext } from "@/lib/auth/validateAuthContext";
+import { safeParseJson } from "@/lib/networking/safeParseJson";
+import { z } from "zod";
+
+export const setupSandboxBodySchema = z.object({
+  account_id: z.string().uuid("account_id must be a valid UUID").optional(),
+});
+
+export type SetupSandboxBody = {
+  accountId: string;
+};
+
+/**
+ * Validates auth and request body for POST /api/sandboxes/setup.
+ * Handles authentication via x-api-key or Authorization bearer token,
+ * body validation, and optional account_id override for organization API keys.
+ *
+ * @param request - The NextRequest object
+ * @returns A NextResponse with an error if validation fails, or the validated body with auth context.
+ */
+export async function validateSetupSandboxBody(
+  request: NextRequest,
+): Promise<NextResponse | SetupSandboxBody> {
+  const body = await safeParseJson(request);
+  const result = setupSandboxBodySchema.safeParse(body);
+
+  if (!result.success) {
+    const firstError = result.error.issues[0];
+    return NextResponse.json(
+      {
+        status: "error",
+        missing_fields: firstError.path,
+        error: firstError.message,
+      },
+      {
+        status: 400,
+        headers: getCorsHeaders(),
+      },
+    );
+  }
+
+  const { account_id: targetAccountId } = result.data;
+
+  const authResult = await validateAuthContext(request, {
+    accountId: targetAccountId,
+  });
+
+  if (authResult instanceof NextResponse) {
+    return authResult;
+  }
+
+  return {
+    accountId: authResult.accountId,
+  };
+}
diff --git a/lib/trigger/__tests__/triggerSetupSandbox.test.ts b/lib/trigger/__tests__/triggerSetupSandbox.test.ts
new file mode 100644
index 00000000..9c35758f
--- /dev/null
+++ b/lib/trigger/__tests__/triggerSetupSandbox.test.ts
@@ -0,0 +1,37 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { triggerSetupSandbox } from "@/lib/trigger/triggerSetupSandbox";
+
+import { tasks } from "@trigger.dev/sdk";
+
+vi.mock("@trigger.dev/sdk", () => ({
+  tasks: {
+    trigger: vi.fn(),
+  },
+}));
+
+describe("triggerSetupSandbox", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("triggers the setup-sandbox task with the accountId", async () => {
+    const mockHandle = { id: "run_abc123" };
+    vi.mocked(tasks.trigger).mockResolvedValue(mockHandle as never);
+
+    const result = await triggerSetupSandbox("account-uuid-123");
+
+    expect(tasks.trigger).toHaveBeenCalledWith("setup-sandbox", {
+      accountId: "account-uuid-123",
+    });
+    expect(result).toEqual(mockHandle);
+  });
+
+  it("returns the task handle with runId", async () => {
+    const mockHandle = { id: "run_xyz789" };
+    vi.mocked(tasks.trigger).mockResolvedValue(mockHandle as never);
+
+    const result = await triggerSetupSandbox("another-account-id");
+
+    expect(result.id).toBe("run_xyz789");
+  });
+});
diff --git a/lib/trigger/triggerSetupSandbox.ts b/lib/trigger/triggerSetupSandbox.ts
new file mode 100644
index 00000000..dec60cb4
--- /dev/null
+++ b/lib/trigger/triggerSetupSandbox.ts
@@ -0,0 +1,13 @@
+import { tasks } from "@trigger.dev/sdk";
+
+/**
+ * Triggers the setup-sandbox task to create a personal sandbox,
+ * provision a GitHub repo, take a snapshot, and shut down.
+ *
+ * @param accountId - The account ID to set up the sandbox for
+ * @returns The task handle with runId
+ */
+export async function triggerSetupSandbox(accountId: string) {
+  const handle = await tasks.trigger("setup-sandbox", { accountId });
+  return handle;
+}