diff --git a/packages/api/src/index.test.ts b/packages/api/src/index.test.ts
new file mode 100644
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--- /dev/null
+++ b/packages/api/src/index.test.ts
@@ -0,0 +1,318 @@
+import { describe, it, expect } from "vitest";
+import {
+  API_VERSION,
+  ENDPOINTS,
+  // Errors
+  ApiErrorResponseSchema,
+  ERROR_CODES,
+  // Pagination
+  PaginationQuerySchema,
+  // Discovery
+  DiscoveryResponseSchema,
+  // Auth
+  TokenExchangeRequestSchema,
+  TokenResponseSchema,
+  DeviceSchema,
+  DeviceListResponseSchema,
+  // Routes
+  RouteSummarySchema,
+  RouteDetailSchema,
+  RouteListResponseSchema,
+  CreateRouteRequestSchema,
+  UpdateRouteRequestSchema,
+  ComputeRouteRequestSchema,
+  // Activities
+  ActivitySummarySchema,
+  ActivityDetailSchema,
+  ActivityListResponseSchema,
+  CreateActivityRequestSchema,
+  // Uploads
+  PresignedUploadRequestSchema,
+  PresignedUploadResponseSchema,
+} from "./index.ts";
+
+describe("API_VERSION", () => {
+  it("is a valid semver string", () => {
+    expect(API_VERSION).toMatch(/^\d+\.\d+\.\d+$/);
+  });
+});
+
+describe("ENDPOINTS", () => {
+  it("has correct static paths", () => {
+    expect(ENDPOINTS.discovery).toBe("/.well-known/trails-cool");
+    expect(ENDPOINTS.routes.list).toBe("/api/v1/routes");
+    expect(ENDPOINTS.activities.list).toBe("/api/v1/activities");
+    expect(ENDPOINTS.auth.token).toBe("/api/v1/auth/token");
+    expect(ENDPOINTS.uploads.presign).toBe("/api/v1/uploads");
+  });
+
+  it("has correct dynamic paths", () => {
+    expect(ENDPOINTS.routes.detail("abc-123")).toBe("/api/v1/routes/abc-123");
+    expect(ENDPOINTS.activities.delete("xyz")).toBe("/api/v1/activities/xyz");
+    expect(ENDPOINTS.auth.device("dev-1")).toBe("/api/v1/auth/devices/dev-1");
+  });
+});
+
+describe("ApiErrorResponseSchema", () => {
+  it("accepts valid error", () => {
+    const result = ApiErrorResponseSchema.parse({
+      error: "Not found",
+      code: "NOT_FOUND",
+    });
+    expect(result.code).toBe("NOT_FOUND");
+  });
+
+  it("accepts error with field errors", () => {
+    const result = ApiErrorResponseSchema.parse({
+      error: "Validation failed",
+      code: ERROR_CODES.VALIDATION_ERROR,
+      fields: [{ field: "name", message: "Required" }],
+    });
+    expect(result.fields).toHaveLength(1);
+  });
+
+  it("rejects missing error field", () => {
+    expect(() => ApiErrorResponseSchema.parse({ code: "X" })).toThrow();
+  });
+});
+
+describe("PaginationQuerySchema", () => {
+  it("defaults limit to 20", () => {
+    const result = PaginationQuerySchema.parse({});
+    expect(result.limit).toBe(20);
+    expect(result.cursor).toBeUndefined();
+  });
+
+  it("coerces string limit", () => {
+    const result = PaginationQuerySchema.parse({ limit: "50" });
+    expect(result.limit).toBe(50);
+  });
+
+  it("rejects limit > 100", () => {
+    expect(() => PaginationQuerySchema.parse({ limit: 101 })).toThrow();
+  });
+});
+
+describe("DiscoveryResponseSchema", () => {
+  it("accepts valid discovery", () => {
+    const result = DiscoveryResponseSchema.parse({
+      apiVersion: "1.0.0",
+      instanceName: "trails.cool",
+      apiBaseUrl: "https://trails.cool/api/v1",
+    });
+    expect(result.apiVersion).toBe("1.0.0");
+  });
+
+  it("accepts optional tileUrl", () => {
+    const result = DiscoveryResponseSchema.parse({
+      apiVersion: "1.0.0",
+      instanceName: "my-instance",
+      apiBaseUrl: "https://example.com/api/v1",
+      tileUrl: "https://tiles.example.com/{z}/{x}/{y}.pbf",
+    });
+    expect(result.tileUrl).toBeDefined();
+  });
+});
+
+describe("TokenExchangeRequestSchema", () => {
+  it("accepts authorization_code grant", () => {
+    const result = TokenExchangeRequestSchema.parse({
+      grant_type: "authorization_code",
+      code: "abc123",
+      code_verifier: "verifier",
+      client_id: "trails-cool-mobile",
+      redirect_uri: "trailscool://auth/callback",
+    });
+    expect(result.grant_type).toBe("authorization_code");
+  });
+
+  it("accepts refresh_token grant", () => {
+    const result = TokenExchangeRequestSchema.parse({
+      grant_type: "refresh_token",
+      refresh_token: "refresh-abc",
+      client_id: "trails-cool-mobile",
+    });
+    expect(result.grant_type).toBe("refresh_token");
+  });
+
+  it("rejects invalid grant_type", () => {
+    expect(() => TokenExchangeRequestSchema.parse({
+      grant_type: "password",
+      client_id: "x",
+    })).toThrow();
+  });
+});
+
+describe("TokenResponseSchema", () => {
+  it("accepts valid token response", () => {
+    const result = TokenResponseSchema.parse({
+      access_token: "at-123",
+      refresh_token: "rt-456",
+      token_type: "Bearer",
+      expires_in: 3600,
+    });
+    expect(result.token_type).toBe("Bearer");
+  });
+});
+
+describe("CreateRouteRequestSchema", () => {
+  it("accepts minimal route", () => {
+    const result = CreateRouteRequestSchema.parse({ name: "My Route" });
+    expect(result.name).toBe("My Route");
+    expect(result.description).toBe("");
+  });
+
+  it("accepts route with GPX", () => {
+    const result = CreateRouteRequestSchema.parse({
+      name: "Berlin Tour",
+      description: "A nice ride",
+      gpx: "<gpx>...</gpx>",
+      routingProfile: "fastbike",
+    });
+    expect(result.gpx).toBeDefined();
+  });
+
+  it("rejects empty name", () => {
+    expect(() => CreateRouteRequestSchema.parse({ name: "" })).toThrow();
+  });
+
+  it("rejects name over 200 chars", () => {
+    expect(() => CreateRouteRequestSchema.parse({ name: "x".repeat(201) })).toThrow();
+  });
+});
+
+describe("UpdateRouteRequestSchema", () => {
+  it("accepts partial update", () => {
+    const result = UpdateRouteRequestSchema.parse({ name: "New Name" });
+    expect(result.name).toBe("New Name");
+    expect(result.gpx).toBeUndefined();
+  });
+
+  it("accepts GPX-only update", () => {
+    const result = UpdateRouteRequestSchema.parse({ gpx: "<gpx>...</gpx>" });
+    expect(result.gpx).toBeDefined();
+  });
+});
+
+describe("ComputeRouteRequestSchema", () => {
+  it("accepts valid waypoints", () => {
+    const result = ComputeRouteRequestSchema.parse({
+      waypoints: [
+        { lat: 52.52, lon: 13.405 },
+        { lat: 52.51, lon: 13.39 },
+      ],
+    });
+    expect(result.waypoints).toHaveLength(2);
+    expect(result.profile).toBe("fastbike");
+  });
+
+  it("rejects fewer than 2 waypoints", () => {
+    expect(() => ComputeRouteRequestSchema.parse({
+      waypoints: [{ lat: 52.52, lon: 13.405 }],
+    })).toThrow();
+  });
+});
+
+describe("RouteSummarySchema", () => {
+  const validRoute = {
+    id: "550e8400-e29b-41d4-a716-446655440000",
+    name: "Berlin Tour",
+    description: "",
+    distance: 42000,
+    elevationGain: 340,
+    elevationLoss: 320,
+    routingProfile: "fastbike",
+    dayBreaks: [2],
+    geojson: null,
+    createdAt: "2026-04-12T10:00:00.000Z",
+    updatedAt: "2026-04-12T12:00:00.000Z",
+  };
+
+  it("accepts valid route summary", () => {
+    const result = RouteSummarySchema.parse(validRoute);
+    expect(result.name).toBe("Berlin Tour");
+  });
+
+  it("accepts nullable fields as null", () => {
+    const result = RouteSummarySchema.parse({
+      ...validRoute,
+      distance: null,
+      elevationGain: null,
+      elevationLoss: null,
+      routingProfile: null,
+    });
+    expect(result.distance).toBeNull();
+  });
+});
+
+describe("RouteListResponseSchema", () => {
+  it("accepts paginated response", () => {
+    const result = RouteListResponseSchema.parse({
+      routes: [],
+      nextCursor: "abc123",
+    });
+    expect(result.nextCursor).toBe("abc123");
+  });
+
+  it("accepts null nextCursor (last page)", () => {
+    const result = RouteListResponseSchema.parse({
+      routes: [],
+      nextCursor: null,
+    });
+    expect(result.nextCursor).toBeNull();
+  });
+});
+
+describe("CreateActivityRequestSchema", () => {
+  it("accepts minimal activity", () => {
+    const result = CreateActivityRequestSchema.parse({ name: "Morning Ride" });
+    expect(result.name).toBe("Morning Ride");
+  });
+
+  it("accepts activity with all fields", () => {
+    const result = CreateActivityRequestSchema.parse({
+      name: "Morning Ride",
+      description: "Nice weather",
+      gpx: "<gpx>...</gpx>",
+      routeId: "550e8400-e29b-41d4-a716-446655440000",
+      startedAt: "2026-04-12T07:00:00.000Z",
+      duration: 3600,
+      distance: 25000,
+    });
+    expect(result.routeId).toBeDefined();
+  });
+});
+
+describe("PresignedUploadRequestSchema", () => {
+  it("accepts valid upload request", () => {
+    const result = PresignedUploadRequestSchema.parse({
+      filename: "photo.jpg",
+      contentType: "image/jpeg",
+      resourceType: "route",
+      resourceId: "550e8400-e29b-41d4-a716-446655440000",
+    });
+    expect(result.resourceType).toBe("route");
+  });
+
+  it("rejects invalid resource type", () => {
+    expect(() => PresignedUploadRequestSchema.parse({
+      filename: "x.jpg",
+      contentType: "image/jpeg",
+      resourceType: "user",
+      resourceId: "550e8400-e29b-41d4-a716-446655440000",
+    })).toThrow();
+  });
+});
+
+describe("DeviceSchema", () => {
+  it("accepts valid device", () => {
+    const result = DeviceSchema.parse({
+      id: "dev-1",
+      deviceName: "iPhone 16e",
+      lastActiveAt: "2026-04-12T10:00:00.000Z",
+      createdAt: "2026-04-10T08:00:00.000Z",
+      isCurrent: true,
+    });
+    expect(result.deviceName).toBe("iPhone 16e");
+  });
+});