diff --git a/packages/api/package.json b/packages/api/package.json
new file mode 100644
index 0000000..42c7511
--- /dev/null
+++ b/packages/api/package.json
@@ -0,0 +1,10 @@
+{
+  "name": "@trails-cool/api",
+  "private": true,
+  "version": "0.0.1",
+  "type": "module",
+  "main": "src/index.ts",
+  "dependencies": {
+    "zod": "^3.25.0"
+  }
+}
diff --git a/packages/api/src/activities.ts b/packages/api/src/activities.ts
new file mode 100644
index 0000000..479fbc6
--- /dev/null
+++ b/packages/api/src/activities.ts
@@ -0,0 +1,45 @@
+import { z } from "zod";
+
+/** Activity summary for list views */
+export const ActivitySummarySchema = z.object({
+  id: z.string().uuid(),
+  name: z.string(),
+  description: z.string(),
+  routeId: z.string().uuid().nullable(),
+  routeName: z.string().nullable(),
+  distance: z.number().nullable(),
+  duration: z.number().nullable(),
+  elevationGain: z.number().nullable(),
+  elevationLoss: z.number().nullable(),
+  startedAt: z.string().datetime().nullable(),
+  geojson: z.string().nullable(),
+  createdAt: z.string().datetime(),
+});
+
+/** Full activity detail */
+export const ActivityDetailSchema = ActivitySummarySchema.extend({
+  gpx: z.string().nullable(),
+  photos: z.array(z.string().url()),
+});
+
+/** Paginated activity list response */
+export const ActivityListResponseSchema = z.object({
+  activities: z.array(ActivitySummarySchema),
+  nextCursor: z.string().nullable(),
+});
+
+/** Create activity request */
+export const CreateActivityRequestSchema = z.object({
+  name: z.string().min(1).max(200),
+  description: z.string().max(5000).default(""),
+  gpx: z.string().optional(),
+  routeId: z.string().uuid().optional(),
+  startedAt: z.string().datetime().optional(),
+  duration: z.number().optional(),
+  distance: z.number().optional(),
+});
+
+export type ActivitySummary = z.infer<typeof ActivitySummarySchema>;
+export type ActivityDetail = z.infer<typeof ActivityDetailSchema>;
+export type ActivityListResponse = z.infer<typeof ActivityListResponseSchema>;
+export type CreateActivityRequest = z.infer<typeof CreateActivityRequestSchema>;
diff --git a/packages/api/src/auth.ts b/packages/api/src/auth.ts
new file mode 100644
index 0000000..8440738
--- /dev/null
+++ b/packages/api/src/auth.ts
@@ -0,0 +1,35 @@
+import { z } from "zod";
+
+export const TokenExchangeRequestSchema = z.object({
+  grant_type: z.enum(["authorization_code", "refresh_token"]),
+  code: z.string().optional(),
+  code_verifier: z.string().optional(),
+  refresh_token: z.string().optional(),
+  client_id: z.string(),
+  redirect_uri: z.string().optional(),
+  device_name: z.string().max(100).optional(),
+});
+
+export const TokenResponseSchema = z.object({
+  access_token: z.string(),
+  refresh_token: z.string(),
+  token_type: z.literal("Bearer"),
+  expires_in: z.number(),
+});
+
+export const DeviceSchema = z.object({
+  id: z.string(),
+  deviceName: z.string().nullable(),
+  lastActiveAt: z.string().datetime(),
+  createdAt: z.string().datetime(),
+  isCurrent: z.boolean(),
+});
+
+export const DeviceListResponseSchema = z.object({
+  devices: z.array(DeviceSchema),
+});
+
+export type TokenExchangeRequest = z.infer<typeof TokenExchangeRequestSchema>;
+export type TokenResponse = z.infer<typeof TokenResponseSchema>;
+export type Device = z.infer<typeof DeviceSchema>;
+export type DeviceListResponse = z.infer<typeof DeviceListResponseSchema>;
diff --git a/packages/api/src/discovery.ts b/packages/api/src/discovery.ts
new file mode 100644
index 0000000..9680a9a
--- /dev/null
+++ b/packages/api/src/discovery.ts
@@ -0,0 +1,10 @@
+import { z } from "zod";
+
+export const DiscoveryResponseSchema = z.object({
+  apiVersion: z.string(),
+  instanceName: z.string(),
+  apiBaseUrl: z.string().url(),
+  tileUrl: z.string().url().optional(),
+});
+
+export type DiscoveryResponse = z.infer<typeof DiscoveryResponseSchema>;
diff --git a/packages/api/src/endpoints.ts b/packages/api/src/endpoints.ts
new file mode 100644
index 0000000..a45d84e
--- /dev/null
+++ b/packages/api/src/endpoints.ts
@@ -0,0 +1,35 @@
+/** Typed API endpoint path constants */
+export const ENDPOINTS = {
+  discovery: "/.well-known/trails-cool",
+
+  auth: {
+    token: "/api/v1/auth/token",
+    devices: "/api/v1/auth/devices",
+    device: (id: string) => `/api/v1/auth/devices/${id}` as const,
+  },
+
+  routes: {
+    list: "/api/v1/routes",
+    create: "/api/v1/routes",
+    detail: (id: string) => `/api/v1/routes/${id}` as const,
+    update: (id: string) => `/api/v1/routes/${id}` as const,
+    delete: (id: string) => `/api/v1/routes/${id}` as const,
+    compute: "/api/v1/routes/compute",
+  },
+
+  activities: {
+    list: "/api/v1/activities",
+    create: "/api/v1/activities",
+    detail: (id: string) => `/api/v1/activities/${id}` as const,
+    delete: (id: string) => `/api/v1/activities/${id}` as const,
+  },
+
+  uploads: {
+    presign: "/api/v1/uploads",
+  },
+
+  push: {
+    subscribe: "/api/v1/push/subscribe",
+    unsubscribe: "/api/v1/push/unsubscribe",
+  },
+} as const;
diff --git a/packages/api/src/errors.ts b/packages/api/src/errors.ts
new file mode 100644
index 0000000..7d7fb88
--- /dev/null
+++ b/packages/api/src/errors.ts
@@ -0,0 +1,26 @@
+import { z } from "zod";
+
+export const FieldErrorSchema = z.object({
+  field: z.string(),
+  message: z.string(),
+});
+
+export const ApiErrorResponseSchema = z.object({
+  error: z.string(),
+  code: z.string(),
+  fields: z.array(FieldErrorSchema).optional(),
+});
+
+export type FieldError = z.infer<typeof FieldErrorSchema>;
+export type ApiErrorResponse = z.infer<typeof ApiErrorResponseSchema>;
+
+/** Standard error codes */
+export const ERROR_CODES = {
+  VALIDATION_ERROR: "VALIDATION_ERROR",
+  NOT_FOUND: "NOT_FOUND",
+  UNAUTHORIZED: "UNAUTHORIZED",
+  FORBIDDEN: "FORBIDDEN",
+  CONFLICT: "CONFLICT",
+  RATE_LIMITED: "RATE_LIMITED",
+  INTERNAL_ERROR: "INTERNAL_ERROR",
+} as const;
diff --git a/packages/api/src/index.ts b/packages/api/src/index.ts
new file mode 100644
index 0000000..8f7e100
--- /dev/null
+++ b/packages/api/src/index.ts
@@ -0,0 +1,56 @@
+export { API_VERSION } from "./version.ts";
+export { ENDPOINTS } from "./endpoints.ts";
+
+// Error schemas
+export {
+  ApiErrorResponseSchema, FieldErrorSchema, ERROR_CODES,
+  type ApiErrorResponse, type FieldError,
+} from "./errors.ts";
+
+// Pagination
+export {
+  PaginationQuerySchema, PaginatedResponseSchema,
+  type PaginationQuery, type PaginatedResponse,
+} from "./pagination.ts";
+
+// Discovery
+export {
+  DiscoveryResponseSchema,
+  type DiscoveryResponse,
+} from "./discovery.ts";
+
+// Auth
+export {
+  TokenExchangeRequestSchema, TokenResponseSchema,
+  DeviceSchema, DeviceListResponseSchema,
+  type TokenExchangeRequest, type TokenResponse,
+  type Device, type DeviceListResponse,
+} from "./auth.ts";
+
+// Routes
+export {
+  RouteSummarySchema, RouteDetailSchema, RouteVersionSchema,
+  RouteListResponseSchema,
+  CreateRouteRequestSchema, UpdateRouteRequestSchema,
+  ComputeRouteRequestSchema,
+  type RouteSummary, type RouteDetail, type RouteVersion,
+  type RouteListResponse,
+  type CreateRouteRequest, type UpdateRouteRequest,
+  type ComputeRouteRequest,
+} from "./routes.ts";
+
+// Activities
+export {
+  ActivitySummarySchema, ActivityDetailSchema,
+  ActivityListResponseSchema,
+  CreateActivityRequestSchema,
+  type ActivitySummary, type ActivityDetail,
+  type ActivityListResponse,
+  type CreateActivityRequest,
+} from "./activities.ts";
+
+// Uploads
+export {
+  PresignedUploadRequestSchema, PresignedUploadResponseSchema,
+  type PresignedUploadRequest, type PresignedUploadResponse,
+} from "./uploads.ts";
diff --git a/packages/api/src/pagination.ts b/packages/api/src/pagination.ts
new file mode 100644
index 0000000..649792f
--- /dev/null
+++ b/packages/api/src/pagination.ts
@@ -0,0 +1,16 @@
+import { z } from "zod";
+
+/** Cursor-based pagination query params */
+export const PaginationQuerySchema = z.object({
+  cursor: z.string().optional(),
+  limit: z.coerce.number().min(1).max(100).default(20),
+});
+
+export type PaginationQuery = z.infer<typeof PaginationQuerySchema>;
+
+/** Paginated response wrapper — extend with your items */
+export const PaginatedResponseSchema = z.object({
+  nextCursor: z.string().nullable(),
+});
+
+export type PaginatedResponse = z.infer<typeof PaginatedResponseSchema>;
diff --git a/packages/api/src/routes.ts b/packages/api/src/routes.ts
new file mode 100644
index 0000000..b9e64e5
--- /dev/null
+++ b/packages/api/src/routes.ts
@@ -0,0 +1,73 @@
+import { z } from "zod";
+
+/** Route summary for list views */
+export const RouteSummarySchema = z.object({
+  id: z.string().uuid(),
+  name: z.string(),
+  description: z.string(),
+  distance: z.number().nullable(),
+  elevationGain: z.number().nullable(),
+  elevationLoss: z.number().nullable(),
+  routingProfile: z.string().nullable(),
+  dayBreaks: z.array(z.number()),
+  geojson: z.string().nullable(),
+  createdAt: z.string().datetime(),
+  updatedAt: z.string().datetime(),
+});
+
+/** Route version info */
+export const RouteVersionSchema = z.object({
+  version: z.number(),
+  changeDescription: z.string().nullable(),
+  createdAt: z.string().datetime(),
+});
+
+/** Full route detail */
+export const RouteDetailSchema = RouteSummarySchema.extend({
+  gpx: z.string().nullable(),
+  versions: z.array(RouteVersionSchema),
+});
+
+/** Paginated route list response */
+export const RouteListResponseSchema = z.object({
+  routes: z.array(RouteSummarySchema),
+  nextCursor: z.string().nullable(),
+});
+
+/** Create route request */
+export const CreateRouteRequestSchema = z.object({
+  name: z.string().min(1).max(200),
+  description: z.string().max(5000).default(""),
+  gpx: z.string().optional(),
+  routingProfile: z.string().optional(),
+});
+
+/** Update route request */
+export const UpdateRouteRequestSchema = z.object({
+  name: z.string().min(1).max(200).optional(),
+  description: z.string().max(5000).optional(),
+  gpx: z.string().optional(),
+});
+
+/** Compute route request (BRouter proxy) */
+export const ComputeRouteRequestSchema = z.object({
+  waypoints: z.array(z.object({
+    lat: z.number(),
+    lon: z.number(),
+  })).min(2),
+  profile: z.string().default("fastbike"),
+  noGoAreas: z.array(z.object({
+    points: z.array(z.object({
+      lat: z.number(),
+      lon: z.number(),
+    })),
+  })).optional(),
+});
+
+export type RouteSummary = z.infer<typeof RouteSummarySchema>;
+export type RouteVersion = z.infer<typeof RouteVersionSchema>;
+export type RouteDetail = z.infer<typeof RouteDetailSchema>;
+export type RouteListResponse = z.infer<typeof RouteListResponseSchema>;
+export type CreateRouteRequest = z.infer<typeof CreateRouteRequestSchema>;
+export type UpdateRouteRequest = z.infer<typeof UpdateRouteRequestSchema>;
+export type ComputeRouteRequest = z.infer<typeof ComputeRouteRequestSchema>;
diff --git a/packages/api/src/uploads.ts b/packages/api/src/uploads.ts
new file mode 100644
index 0000000..98f8927
--- /dev/null
+++ b/packages/api/src/uploads.ts
@@ -0,0 +1,17 @@
+import { z } from "zod";
+
+export const PresignedUploadRequestSchema = z.object({
+  filename: z.string(),
+  contentType: z.string(),
+  resourceType: z.enum(["route", "activity"]),
+  resourceId: z.string().uuid(),
+});
+
+export const PresignedUploadResponseSchema = z.object({
+  uploadUrl: z.string().url(),
+  storageKey: z.string(),
+  expiresAt: z.string().datetime(),
+});
+
+export type PresignedUploadRequest = z.infer<typeof PresignedUploadRequestSchema>;
+export type PresignedUploadResponse = z.infer<typeof PresignedUploadResponseSchema>;
diff --git a/packages/api/src/version.ts b/packages/api/src/version.ts
new file mode 100644
index 0000000..5ef45ad
--- /dev/null
+++ b/packages/api/src/version.ts
@@ -0,0 +1,7 @@
+/**
+ * API version following semver.
+ * - Patch: bug fixes
+ * - Minor: new endpoints, new optional fields (backwards compatible)
+ * - Major: breaking changes
+ */
+export const API_VERSION = "1.0.0";
diff --git a/packages/api/tsconfig.json b/packages/api/tsconfig.json
new file mode 100644
index 0000000..5285d28
--- /dev/null
+++ b/packages/api/tsconfig.json
@@ -0,0 +1,8 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "dist"
+  },
+  "include": ["src"]
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 9f75fd4..42d9ac7 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -410,6 +410,12 @@ importers:
         specifier: 'catalog:'
         version: 8.0.8(@types/node@25.5.2)(esbuild@0.27.4)(jiti@2.6.1)(tsx@4.21.0)
 
+  packages/api:
+    dependencies:
+      zod:
+        specifier: ^3.25.0
+        version: 3.25.76
+
   packages/db:
     dependencies:
       drizzle-orm:
@@ -4102,6 +4108,9 @@ packages:
     resolution: {integrity: sha512-rVksvsnNCdJ/ohGc6xgPwyN8eheCxsiLM8mxuE/t/mOVqJewPuO1miLpTHQiRgTKCLexL4MeAFVagts7HmNZ2Q==}
     engines: {node: '>=10'}
 
+  zod@3.25.76:
+    resolution: {integrity: sha512-gzUt/qt81nXsFGKIFcC3YnfEAx5NkunCfnDlvuBSSFS02bcXu4Lmea0AFIUwbLWxWPx3d9p8S5QoaujKcNQxcQ==}
+
 snapshots:
 
   '@adobe/css-tools@4.4.4': {}
@@ -7620,3 +7629,5 @@ snapshots:
       lib0: 0.2.117
 
   yocto-queue@0.1.0: {}
+
+  zod@3.25.76: {}