diff --git a/backend/internal/discovery/discovery.go b/backend/internal/discovery/discovery.go
new file mode 100644
index 0000000..011223b
--- /dev/null
+++ b/backend/internal/discovery/discovery.go
@@ -0,0 +1,129 @@
+// Package discovery finds Apollo/Artemis hosts on the network via mDNS.
+// Apollo advertises itself as _nvstream._tcp.local — the same service
+// type that Moonlight scans for.
+package discovery
+
+import (
+	"context"
+	"log"
+	"sync"
+	"time"
+
+	"github.com/grandcat/zeroconf"
+)
+
+const nvstreamService = "_nvstream._tcp"
+
+// Host represents a discovered Apollo/Artemis streaming host.
+type Host struct {
+	Name    string   `json:"name"`
+	IP      string   `json:"ip"`
+	Port    int      `json:"port"`
+	Online  bool     `json:"online"`
+	SeenAt  time.Time `json:"seen_at"`
+}
+
+// Discoverer watches the local (Tailscale) network for Apollo hosts.
+type Discoverer struct {
+	mu    sync.RWMutex
+	hosts map[string]*Host // keyed by name
+}
+
+// New creates a new Discoverer with an empty host list.
+func New() *Discoverer {
+	return &Discoverer{hosts: make(map[string]*Host)}
+}
+
+// Run starts mDNS browsing and blocks until ctx is cancelled.
+// Discovered hosts are stored and retrievable via Hosts().
+func (d *Discoverer) Run(ctx context.Context) {
+	for {
+		if err := d.browse(ctx); err != nil && ctx.Err() == nil {
+			log.Printf("discovery: browse error: %v — retrying in 10s", err)
+			select {
+			case <-ctx.Done():
+				return
+			case <-time.After(10 * time.Second):
+			}
+		}
+		if ctx.Err() != nil {
+			return
+		}
+	}
+}
+
+func (d *Discoverer) browse(ctx context.Context) error {
+	resolver, err := zeroconf.NewResolver(nil)
+	if err != nil {
+		return err
+	}
+
+	entries := make(chan *zeroconf.ServiceEntry)
+	browseCtx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	go func() {
+		for entry := range entries {
+			ip := ""
+			if len(entry.AddrIPv4) > 0 {
+				ip = entry.AddrIPv4[0].String()
+			} else if len(entry.AddrIPv6) > 0 {
+				ip = entry.AddrIPv6[0].String()
+			}
+			if ip == "" {
+				continue
+			}
+			h := &Host{
+				Name:   entry.ServiceInstanceName(),
+				IP:     ip,
+				Port:   entry.Port,
+				Online: true,
+				SeenAt: time.Now(),
+			}
+			d.upsert(h)
+			log.Printf("discovery: found host %s at %s:%d", h.Name, h.IP, h.Port)
+		}
+	}()
+
+	if err := resolver.Browse(browseCtx, nvstreamService, "local.", entries); err != nil {
+		return err
+	}
+	<-browseCtx.Done()
+	return nil
+}
+
+func (d *Discoverer) upsert(h *Host) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	d.hosts[h.Name] = h
+}
+
+// Hosts returns a snapshot of all known hosts.
+func (d *Discoverer) Hosts() []*Host {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	// Mark hosts as offline if not seen in 30s
+	cutoff := time.Now().Add(-30 * time.Second)
+	out := make([]*Host, 0, len(d.hosts))
+	for _, h := range d.hosts {
+		copy := *h
+		if h.SeenAt.Before(cutoff) {
+			copy.Online = false
+		}
+		out = append(out, &copy)
+	}
+	return out
+}
+
+// AddManual adds a host by IP/port without mDNS (for hosts behind NAT or
+// on subnets that don't support multicast).
+func (d *Discoverer) AddManual(name, ip string, port int) {
+	d.upsert(&Host{
+		Name:   name,
+		IP:     ip,
+		Port:   port,
+		Online: true,
+		SeenAt: time.Now(),
+	})
+}