diff --git a/main.go b/main.go
index d131ba0..53d07e7 100644
--- a/main.go
+++ b/main.go
@@ -1 +1,5 @@
+// Package dyzurbot is a Telegram duty-rota bot. It serves the rota from a
+// local cache (see Store) that is periodically actualized from Google Sheets
+// (see Syncer/Service). Telegram handlers and reminders are built on top of
+// Service and read via Store.Snapshot.
 package dyzurbot
diff --git a/service.go b/service.go
new file mode 100644
index 0000000..f611c02
--- /dev/null
+++ b/service.go
@@ -0,0 +1,75 @@
+package dyzurbot
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/joho/godotenv"
+)
+
+// Config holds the cache/sync settings, sourced from the environment/.env.
+type Config struct {
+	SpreadsheetID string
+	SheetRange    string
+	CachePath     string
+	SyncInterval  time.Duration
+}
+
+// LoadConfig reads configuration from the environment (and .env if present),
+// applying defaults for everything except the required spreadsheet ID.
+func LoadConfig() (Config, error) {
+	_ = godotenv.Load()
+
+	cfg := Config{
+		SpreadsheetID: os.Getenv("SPREADSHEET_ID"),
+		SheetRange:    getenvDefault("SHEET_RANGE", "Dyżury!A1:F100"),
+		CachePath:     getenvDefault("ROTA_CACHE_PATH", "rota.json"),
+	}
+	if cfg.SpreadsheetID == "" {
+		return Config{}, fmt.Errorf("missing SPREADSHEET_ID in environment/.env")
+	}
+
+	raw := getenvDefault("SYNC_INTERVAL", "30m")
+	interval, err := time.ParseDuration(raw)
+	if err != nil {
+		return Config{}, fmt.Errorf("invalid SYNC_INTERVAL %q: %w", raw, err)
+	}
+	cfg.SyncInterval = interval
+
+	return cfg, nil
+}
+
+func getenvDefault(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return fallback
+}
+
+// Service ties the Store and Syncer together for the bot to consume.
+type Service struct {
+	Store    *Store
+	Syncer   *Syncer
+	interval time.Duration
+}
+
+// NewService builds the cache + syncer from config.
+func NewService(cfg Config) *Service {
+	store := NewStore(cfg.CachePath)
+	syncer := NewSyncer(store, SheetFetcher(cfg.SpreadsheetID, cfg.SheetRange))
+	return &Service{Store: store, Syncer: syncer, interval: cfg.SyncInterval}
+}
+
+// Start loads the cached rota, runs one best-effort sync (a failure leaves the
+// cached/empty data in place — offline-tolerant), then polls in the background
+// until ctx is canceled.
+func (s *Service) Start(ctx context.Context) error {
+	if err := s.Store.Load(); err != nil {
+		return err
+	}
+	_ = s.Syncer.Sync(ctx)
+	go s.Syncer.Run(ctx, s.interval)
+	return nil
+}
diff --git a/service_test.go b/service_test.go
new file mode 100644
index 0000000..32df135
--- /dev/null
+++ b/service_test.go
@@ -0,0 +1,45 @@
+package dyzurbot
+
+import (
+	"testing"
+	"time"
+)
+
+func TestLoadConfigDefaults(t *testing.T) {
+	t.Setenv("SPREADSHEET_ID", "sheet-123")
+	t.Setenv("SHEET_RANGE", "")
+	t.Setenv("ROTA_CACHE_PATH", "")
+	t.Setenv("SYNC_INTERVAL", "")
+
+	cfg, err := LoadConfig()
+	if err != nil {
+		t.Fatalf("LoadConfig: %v", err)
+	}
+	if cfg.SpreadsheetID != "sheet-123" {
+		t.Errorf("SpreadsheetID: got %q", cfg.SpreadsheetID)
+	}
+	if cfg.SheetRange != "Dyżury!A1:F100" {
+		t.Errorf("SheetRange default: got %q", cfg.SheetRange)
+	}
+	if cfg.CachePath != "rota.json" {
+		t.Errorf("CachePath default: got %q", cfg.CachePath)
+	}
+	if cfg.SyncInterval != 30*time.Minute {
+		t.Errorf("SyncInterval default: got %v", cfg.SyncInterval)
+	}
+}
+
+func TestLoadConfigRequiresSpreadsheetID(t *testing.T) {
+	t.Setenv("SPREADSHEET_ID", "")
+	if _, err := LoadConfig(); err == nil {
+		t.Fatal("expected error when SPREADSHEET_ID is missing")
+	}
+}
+
+func TestLoadConfigRejectsBadInterval(t *testing.T) {
+	t.Setenv("SPREADSHEET_ID", "sheet-123")
+	t.Setenv("SYNC_INTERVAL", "not-a-duration")
+	if _, err := LoadConfig(); err == nil {
+		t.Fatal("expected error for unparseable SYNC_INTERVAL")
+	}
+}