diff --git a/main.go b/main.go
index c58bd20..175e538 100644
--- a/main.go
+++ b/main.go
@@ -728,7 +728,7 @@ func importCategory(st Store, cat, url string) (int, error) {
 	return count, sc.Err()
 }
 
-func startImporter(st Store, cats map[string]string) {
+func startImporter(st Store, cats map[string]string, srv *server) {
 	go func() {
 		for {
 			start := time.Now()
@@ -752,6 +752,7 @@ func startImporter(st Store, cats map[string]string) {
 				}()
 			}
 			wg.Wait()
+			srv.rebuildIndex()
 			atomic.AddUint64(&metrics.importerCycles, 1)
 			atomic.StoreInt64(&metrics.importerLastSuccess, time.Now().Unix())
 			log.Printf("Import cycle finished in %s", time.Since(start))
@@ -764,10 +765,74 @@ func startImporter(st Store, cats map[string]string) {
 // HTTP layer
 // ──────────────────────────────────────────────────────────────────────────────
 
+type ipIndex struct {
+	v4Lens []int // vorhandene Präfixlängen (z. B. 8, 16, 24, 32)
+	v6Lens []int
+	v4     map[int]map[string][]string // len -> "a.b.c.d/len" -> []categories
+	v6     map[int]map[string][]string // len -> "xxxx::/len" -> []categories
+}
+
 type server struct {
 	st      Store
 	catalog map[string]string // latest catalog for category list
 	mu      sync.RWMutex
+	idx     atomic.Value
+}
+
+func (s *server) rebuildIndex() {
+	idx := &ipIndex{v4: map[int]map[string][]string{}, v6: map[int]map[string][]string{}}
+	lens4 := map[int]struct{}{}
+	lens6 := map[int]struct{}{}
+
+	cats := s.cats()
+	for _, c := range cats {
+		pfxs, _ := s.st.ListPrefixes(c)
+		for _, p := range pfxs {
+			m := idx.v6
+			lens := lens6
+			if p.Addr().Is4() {
+				m = idx.v4
+				lens = lens4
+			}
+			l := int(p.Bits())
+			if m[l] == nil {
+				m[l] = map[string][]string{}
+			}
+			k := p.String()
+			m[l][k] = append(m[l][k], c)
+			lens[l] = struct{}{}
+		}
+	}
+	// manuelle Blacklist mit aufnehmen (als Kategorie "manual-blacklist")
+	if bl, err := s.st.ListBlacklist(); err == nil {
+		for p := range bl {
+			m := idx.v6
+			lens := lens6
+			if p.Addr().Is4() {
+				m = idx.v4
+				lens = lens4
+			}
+			l := int(p.Bits())
+			if m[l] == nil {
+				m[l] = map[string][]string{}
+			}
+			k := p.String()
+			m[l][k] = append(m[l][k], "manual-blacklist")
+			lens[l] = struct{}{}
+		}
+	}
+
+	// Längen sortiert ablegen (damit Lookup nur vorhandene prüft)
+	for l := range lens4 {
+		idx.v4Lens = append(idx.v4Lens, l)
+	}
+	for l := range lens6 {
+		idx.v6Lens = append(idx.v6Lens, l)
+	}
+	sort.Ints(idx.v4Lens)
+	sort.Ints(idx.v6Lens)
+
+	s.idx.Store(idx)
 }
 
 func (s *server) cats() []string {
@@ -1310,32 +1375,30 @@ func (s *server) handleBlacklistList(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, map[string]any{"entries": list})
 }
 
-func (s *server) checkIP(ip netip.Addr, cats []string) ([]string, error) {
-	// 1) Whitelist gewinnt
+func (s *server) checkIP(ip netip.Addr, _ []string) ([]string, error) {
 	if ok, _ := s.st.IsWhitelisted(ip); ok {
 		return nil, nil
 	}
 
-	// 2) Manuelle Blacklist
-	bl, _ := s.st.ListBlacklist()
-	for pfx := range bl {
-		if pfx.Contains(ip) {
-			// "manual-blacklist" als erste Kategorie markieren
-			return []string{"manual-blacklist"}, nil
-		}
+	idx := s.idx.Load().(*ipIndex)
+	var lens []int
+	var m map[int]map[string][]string
+	if ip.Is4() {
+		lens, m = idx.v4Lens, idx.v4
+	} else {
+		lens, m = idx.v6Lens, idx.v6
 	}
 
-	// 3) Import-Kategorien
+	seen := map[string]struct{}{}
 	var matches []string
-	for _, c := range cats {
-		pfxs, err := s.st.ListPrefixes(c)
-		if err != nil {
-			return nil, err
-		}
-		for _, p := range pfxs {
-			if p.Contains(ip) {
-				matches = append(matches, c)
-				break
+	for _, l := range lens {
+		p := netip.PrefixFrom(ip, l).String()
+		if cats, ok := m[l][p]; ok {
+			for _, c := range cats {
+				if _, dup := seen[c]; !dup {
+					seen[c] = struct{}{}
+					matches = append(matches, c)
+				}
 			}
 		}
 	}
@@ -1428,7 +1491,7 @@ func main() {
 		}
 	}
 	srv := &server{st: st, catalog: cat}
-	startImporter(st, cat)
+	startImporter(st, cat, srv)
 
 	// honeypot listeners
 	if enableHoneypot {