diff --git a/cmd/sdrd/hub.go b/cmd/sdrd/hub.go
new file mode 100644
index 0000000..382b398
--- /dev/null
+++ b/cmd/sdrd/hub.go
@@ -0,0 +1,85 @@
+package main
+
+import (
+	"encoding/json"
+	"log"
+	"time"
+
+	"sdr-visual-suite/internal/detector"
+)
+
+func (s *signalSnapshot) set(sig []detector.Signal) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.signals = append([]detector.Signal(nil), sig...)
+}
+
+func (s *signalSnapshot) get() []detector.Signal {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	return append([]detector.Signal(nil), s.signals...)
+}
+
+func (g *gpuStatus) set(active bool, err error) {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+	g.Active = active
+	if err != nil {
+		g.Error = err.Error()
+	} else {
+		g.Error = ""
+	}
+}
+
+func (g *gpuStatus) snapshot() gpuStatus {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+	return gpuStatus{Available: g.Available, Active: g.Active, Error: g.Error}
+}
+
+func newHub() *hub {
+	return &hub{clients: map[*client]struct{}{}, lastLogTs: time.Now()}
+}
+
+func (h *hub) add(c *client) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	h.clients[c] = struct{}{}
+	log.Printf("ws connected (%d clients)", len(h.clients))
+}
+
+func (h *hub) remove(c *client) {
+	c.closeOnce.Do(func() { close(c.done) })
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	delete(h.clients, c)
+	log.Printf("ws disconnected (%d clients)", len(h.clients))
+}
+
+func (h *hub) broadcast(frame SpectrumFrame) {
+	b, err := json.Marshal(frame)
+	if err != nil {
+		log.Printf("marshal frame: %v", err)
+		return
+	}
+
+	h.mu.Lock()
+	clients := make([]*client, 0, len(h.clients))
+	for c := range h.clients {
+		clients = append(clients, c)
+	}
+	h.mu.Unlock()
+
+	for _, c := range clients {
+		select {
+		case c.send <- b:
+		default:
+			h.remove(c)
+		}
+	}
+	h.frameCnt++
+	if time.Since(h.lastLogTs) > 2*time.Second {
+		h.lastLogTs = time.Now()
+		log.Printf("broadcast frames=%d clients=%d", h.frameCnt, len(clients))
+	}
+}
diff --git a/cmd/sdrd/main.go b/cmd/sdrd/main.go
index fd72ef1..f9cf8fa 100644
--- a/cmd/sdrd/main.go
+++ b/cmd/sdrd/main.go
@@ -34,237 +34,6 @@ import (
 	"sdr-visual-suite/internal/sdrplay"
 )
 
-type SpectrumDebug struct {
-	Thresholds []float64                 `json:"thresholds,omitempty"`
-	NoiseFloor float64                   `json:"noise_floor,omitempty"`
-	Scores     []map[string]any          `json:"scores,omitempty"`
-}
-
-type SpectrumFrame struct {
-	Timestamp int64             `json:"ts"`
-	CenterHz  float64           `json:"center_hz"`
-	SampleHz  int               `json:"sample_rate"`
-	FFTSize   int               `json:"fft_size"`
-	Spectrum  []float64         `json:"spectrum_db"`
-	Signals   []detector.Signal `json:"signals"`
-	Debug     *SpectrumDebug    `json:"debug,omitempty"`
-}
-
-type client struct {
-	conn      *websocket.Conn
-	send      chan []byte
-	done      chan struct{}
-	closeOnce sync.Once
-}
-
-type hub struct {
-	mu        sync.Mutex
-	clients   map[*client]struct{}
-	frameCnt  int64
-	lastLogTs time.Time
-}
-
-type gpuStatus struct {
-	mu        sync.RWMutex
-	Available bool   `json:"available"`
-	Active    bool   `json:"active"`
-	Error     string `json:"error"`
-}
-
-type signalSnapshot struct {
-	mu      sync.RWMutex
-	signals []detector.Signal
-}
-
-func (s *signalSnapshot) set(sig []detector.Signal) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	s.signals = append([]detector.Signal(nil), sig...)
-}
-
-func (s *signalSnapshot) get() []detector.Signal {
-	s.mu.RLock()
-	defer s.mu.RUnlock()
-	return append([]detector.Signal(nil), s.signals...)
-}
-
-func (g *gpuStatus) set(active bool, err error) {
-	g.mu.Lock()
-	defer g.mu.Unlock()
-	g.Active = active
-	if err != nil {
-		g.Error = err.Error()
-	} else {
-		g.Error = ""
-	}
-}
-
-func (g *gpuStatus) snapshot() gpuStatus {
-	g.mu.RLock()
-	defer g.mu.RUnlock()
-	return gpuStatus{Available: g.Available, Active: g.Active, Error: g.Error}
-}
-
-func newHub() *hub {
-	return &hub{clients: map[*client]struct{}{}, lastLogTs: time.Now()}
-}
-
-func (h *hub) add(c *client) {
-	h.mu.Lock()
-	defer h.mu.Unlock()
-	h.clients[c] = struct{}{}
-	log.Printf("ws connected (%d clients)", len(h.clients))
-}
-
-func (h *hub) remove(c *client) {
-	c.closeOnce.Do(func() { close(c.done) })
-	h.mu.Lock()
-	defer h.mu.Unlock()
-	delete(h.clients, c)
-	log.Printf("ws disconnected (%d clients)", len(h.clients))
-}
-
-func (h *hub) broadcast(frame SpectrumFrame) {
-	b, err := json.Marshal(frame)
-	if err != nil {
-		log.Printf("marshal frame: %v", err)
-		return
-	}
-
-	h.mu.Lock()
-	clients := make([]*client, 0, len(h.clients))
-	for c := range h.clients {
-		clients = append(clients, c)
-	}
-	h.mu.Unlock()
-
-	for _, c := range clients {
-		select {
-		case c.send <- b:
-		default:
-			h.remove(c)
-		}
-	}
-	h.frameCnt++
-	if time.Since(h.lastLogTs) > 2*time.Second {
-		h.lastLogTs = time.Now()
-		log.Printf("broadcast frames=%d clients=%d", h.frameCnt, len(clients))
-	}
-}
-
-type sourceManager struct {
-	mu        sync.RWMutex
-	src       sdr.Source
-	newSource func(cfg config.Config) (sdr.Source, error)
-}
-
-func (m *sourceManager) Restart(cfg config.Config) error {
-	m.mu.Lock()
-	defer m.mu.Unlock()
-	old := m.src
-	_ = old.Stop()
-	next, err := m.newSource(cfg)
-	if err != nil {
-		_ = old.Start()
-		m.src = old
-		return err
-	}
-	if err := next.Start(); err != nil {
-		_ = next.Stop()
-		_ = old.Start()
-		m.src = old
-		return err
-	}
-	m.src = next
-	return nil
-}
-
-func (m *sourceManager) Stats() sdr.SourceStats {
-	m.mu.RLock()
-	defer m.mu.RUnlock()
-	if sp, ok := m.src.(sdr.StatsProvider); ok {
-		return sp.Stats()
-	}
-	return sdr.SourceStats{}
-}
-
-func (m *sourceManager) Flush() {
-	m.mu.RLock()
-	defer m.mu.RUnlock()
-	if fl, ok := m.src.(sdr.Flushable); ok {
-		fl.Flush()
-	}
-}
-
-func newSourceManager(src sdr.Source, newSource func(cfg config.Config) (sdr.Source, error)) *sourceManager {
-	return &sourceManager{src: src, newSource: newSource}
-}
-
-func (m *sourceManager) Start() error {
-	m.mu.RLock()
-	defer m.mu.RUnlock()
-	return m.src.Start()
-}
-
-func (m *sourceManager) Stop() error {
-	m.mu.RLock()
-	defer m.mu.RUnlock()
-	return m.src.Stop()
-}
-
-func (m *sourceManager) ReadIQ(n int) ([]complex64, error) {
-	m.mu.RLock()
-	defer m.mu.RUnlock()
-	return m.src.ReadIQ(n)
-}
-
-func (m *sourceManager) ApplyConfig(cfg config.Config) error {
-	m.mu.Lock()
-	defer m.mu.Unlock()
-
-	if updatable, ok := m.src.(sdr.ConfigurableSource); ok {
-		if err := updatable.UpdateConfig(cfg.SampleRate, cfg.CenterHz, cfg.GainDb, cfg.AGC, cfg.TunerBwKHz); err == nil {
-			return nil
-		}
-	}
-
-	old := m.src
-	_ = old.Stop()
-	next, err := m.newSource(cfg)
-	if err != nil {
-		_ = old.Start()
-		return err
-	}
-	if err := next.Start(); err != nil {
-		_ = next.Stop()
-		_ = old.Start()
-		return err
-	}
-	m.src = next
-	return nil
-}
-
-type dspUpdate struct {
-	cfg       config.Config
-	det       *detector.Detector
-	window    []float64
-	dcBlock   bool
-	iqBalance bool
-	useGPUFFT bool
-}
-
-func pushDSPUpdate(ch chan dspUpdate, update dspUpdate) {
-	select {
-	case ch <- update:
-	default:
-		select {
-		case <-ch:
-		default:
-		}
-		ch <- update
-	}
-}
-
 func main() {
 	var cfgPath string
 	var mockFlag bool
@@ -966,3 +735,4 @@ func parseSince(raw string) (time.Time, error) {
 	}
 	return time.Parse(time.RFC3339, raw)
 }
+
diff --git a/cmd/sdrd/source_manager.go b/cmd/sdrd/source_manager.go
new file mode 100644
index 0000000..c9a664c
--- /dev/null
+++ b/cmd/sdrd/source_manager.go
@@ -0,0 +1,104 @@
+package main
+
+import (
+	"sdr-visual-suite/internal/config"
+	"sdr-visual-suite/internal/sdr"
+)
+
+func (m *sourceManager) Restart(cfg config.Config) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	old := m.src
+	_ = old.Stop()
+	next, err := m.newSource(cfg)
+	if err != nil {
+		_ = old.Start()
+		m.src = old
+		return err
+	}
+	if err := next.Start(); err != nil {
+		_ = next.Stop()
+		_ = old.Start()
+		m.src = old
+		return err
+	}
+	m.src = next
+	return nil
+}
+
+func (m *sourceManager) Stats() sdr.SourceStats {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	if sp, ok := m.src.(sdr.StatsProvider); ok {
+		return sp.Stats()
+	}
+	return sdr.SourceStats{}
+}
+
+func (m *sourceManager) Flush() {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	if fl, ok := m.src.(sdr.Flushable); ok {
+		fl.Flush()
+	}
+}
+
+func newSourceManager(src sdr.Source, newSource func(cfg config.Config) (sdr.Source, error)) *sourceManager {
+	return &sourceManager{src: src, newSource: newSource}
+}
+
+func (m *sourceManager) Start() error {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return m.src.Start()
+}
+
+func (m *sourceManager) Stop() error {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return m.src.Stop()
+}
+
+func (m *sourceManager) ReadIQ(n int) ([]complex64, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return m.src.ReadIQ(n)
+}
+
+func (m *sourceManager) ApplyConfig(cfg config.Config) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if updatable, ok := m.src.(sdr.ConfigurableSource); ok {
+		if err := updatable.UpdateConfig(cfg.SampleRate, cfg.CenterHz, cfg.GainDb, cfg.AGC, cfg.TunerBwKHz); err == nil {
+			return nil
+		}
+	}
+
+	old := m.src
+	_ = old.Stop()
+	next, err := m.newSource(cfg)
+	if err != nil {
+		_ = old.Start()
+		return err
+	}
+	if err := next.Start(); err != nil {
+		_ = next.Stop()
+		_ = old.Start()
+		return err
+	}
+	m.src = next
+	return nil
+}
+
+func pushDSPUpdate(ch chan dspUpdate, update dspUpdate) {
+	select {
+	case ch <- update:
+	default:
+		select {
+		case <-ch:
+		default:
+		}
+		ch <- update
+	}
+}
diff --git a/cmd/sdrd/types.go b/cmd/sdrd/types.go
new file mode 100644
index 0000000..1c21d88
--- /dev/null
+++ b/cmd/sdrd/types.go
@@ -0,0 +1,69 @@
+package main
+
+import (
+	"sync"
+	"time"
+
+	"github.com/gorilla/websocket"
+
+	"sdr-visual-suite/internal/config"
+	"sdr-visual-suite/internal/detector"
+	"sdr-visual-suite/internal/sdr"
+)
+
+type SpectrumDebug struct {
+	Thresholds []float64        `json:"thresholds,omitempty"`
+	NoiseFloor float64          `json:"noise_floor,omitempty"`
+	Scores     []map[string]any `json:"scores,omitempty"`
+}
+
+type SpectrumFrame struct {
+	Timestamp int64             `json:"ts"`
+	CenterHz  float64           `json:"center_hz"`
+	SampleHz  int               `json:"sample_rate"`
+	FFTSize   int               `json:"fft_size"`
+	Spectrum  []float64         `json:"spectrum_db"`
+	Signals   []detector.Signal `json:"signals"`
+	Debug     *SpectrumDebug    `json:"debug,omitempty"`
+}
+
+type client struct {
+	conn      *websocket.Conn
+	send      chan []byte
+	done      chan struct{}
+	closeOnce sync.Once
+}
+
+type hub struct {
+	mu        sync.Mutex
+	clients   map[*client]struct{}
+	frameCnt  int64
+	lastLogTs time.Time
+}
+
+type gpuStatus struct {
+	mu        sync.RWMutex
+	Available bool   `json:"available"`
+	Active    bool   `json:"active"`
+	Error     string `json:"error"`
+}
+
+type signalSnapshot struct {
+	mu      sync.RWMutex
+	signals []detector.Signal
+}
+
+type sourceManager struct {
+	mu        sync.RWMutex
+	src       sdr.Source
+	newSource func(cfg config.Config) (sdr.Source, error)
+}
+
+type dspUpdate struct {
+	cfg       config.Config
+	det       *detector.Detector
+	window    []float64
+	dcBlock   bool
+	iqBalance bool
+	useGPUFFT bool
+}
diff --git a/web/app.js b/web/app.js
index 9acd865..a676bad 100644
--- a/web/app.js
+++ b/web/app.js
@@ -151,7 +151,8 @@ let timelineRects = [];
 let liveSignalRects = [];
 let recordings = [];
 let recordingsFetchInFlight = false;
-let showDebugOverlay = true;
+let showDebugOverlay = localStorage.getItem('spectre.debugOverlay') !== '0';
+let hoveredSignal = null;
 let showDebugOverlay = true;
 
 const GAIN_MAX = 60;
@@ -184,16 +185,17 @@ function fmtMs(ms) {
   return `${(ms / 1000).toFixed(2)} s`;
 }
 
-function renderScoreBars(scores) {
-  if (!classifierScoreBarsEl) return;
-  if (!scores || typeof scores !== 'object') {
-    classifierScoreBarsEl.innerHTML = '';
-    return;
-  }
-  const entries = Object.entries(scores)
+function scoreEntries(scores, limit = 6) {
+  if (!scores || typeof scores !== 'object') return [];
+  return Object.entries(scores)
     .filter(([, v]) => Number.isFinite(Number(v)))
     .sort((a, b) => Number(b[1]) - Number(a[1]))
-    .slice(0, 6);
+    .slice(0, limit);
+}
+
+function renderScoreBars(scores) {
+  if (!classifierScoreBarsEl) return;
+  const entries = scoreEntries(scores);
   if (!entries.length) {
     classifierScoreBarsEl.innerHTML = '';
     return;
@@ -205,6 +207,28 @@ function renderScoreBars(scores) {
   }).join('');
 }
 
+function hideSignalPopover() {
+  hoveredSignal = null;
+  if (!signalPopover) return;
+  signalPopover.classList.remove('open');
+  signalPopover.setAttribute('aria-hidden', 'true');
+}
+
+function renderSignalPopover(rect, signal) {
+  if (!signalPopover || !signal) return;
+  const entries = scoreEntries(signal.class?.scores || signal.debug_scores || {}, 4);
+  const maxVal = Math.max(...entries.map(([, v]) => Number(v)), 1e-6);
+  const rows = entries.map(([label, value]) => {
+    const width = Math.max(4, (Number(value) / maxVal) * 100);
+    return `<div class="signal-popover__row"><span>${label}</span><span class="signal-popover__bar"><span class="signal-popover__fill" style="width:${width}%"></span></span><span>${Number(value).toFixed(2)}</span></div>`;
+  }).join('');
+  signalPopover.innerHTML = `<div class="signal-popover__title">${signal.class?.mod_type || 'Signal'}</div><div class="signal-popover__meta">${fmtMHz(signal.center_hz, 5)} · ${fmtKHz(signal.bw_hz || 0)} · ${(signal.snr_db || 0).toFixed(1)} dB SNR</div><div class="signal-popover__scores">${rows || '<div class="signal-popover__meta">No classifier scores</div>'}</div>`;
+  signalPopover.style.left = `${Math.max(8, rect.x + rect.w + 8)}px`;
+  signalPopover.style.top = `${Math.max(8, rect.y + 8)}px`;
+  signalPopover.classList.add('open');
+  signalPopover.setAttribute('aria-hidden', 'false');
+}
+
 function colorMap(v) {
   const x = Math.max(0, Math.min(1, v));
   const r = Math.floor(255 * Math.pow(x, 0.55));
@@ -731,6 +755,10 @@ function renderSpectrum() {
       const label = `${(s.center_hz / 1e6).toFixed(4)} MHz`;
       ctx.fillText(label, Math.max(4, x1 + 4), 24 + (index % 3) * 16);
 
+      const debugMatch = (latest?.debug?.scores || []).find((d) => Math.abs((d.center_hz || 0) - (s.center_hz || 0)) < Math.max(500, s.bw_hz || 0));
+      if (debugMatch?.scores && (!s.class || !s.class.scores)) {
+        s.debug_scores = debugMatch.scores;
+      }
       liveSignalRects.push({
         x: x1,
         y: 10,
@@ -1242,7 +1270,25 @@ window.addEventListener('mouseup', () => {
   isDraggingSpectrum = false;
   navDrag = false;
 });
+spectrumCanvas.addEventListener('mouseleave', hideSignalPopover);
 window.addEventListener('mousemove', (ev) => {
+  const rect = spectrumCanvas.getBoundingClientRect();
+  const x = (ev.clientX - rect.left) * (spectrumCanvas.width / rect.width);
+  const y = (ev.clientY - rect.top) * (spectrumCanvas.height / rect.height);
+  let hoverHit = null;
+  for (let i = liveSignalRects.length - 1; i >= 0; i--) {
+    const r = liveSignalRects[i];
+    if (x >= r.x && x <= r.x + r.w && y >= r.y && y <= r.y + r.h) {
+      hoverHit = r;
+      break;
+    }
+  }
+  if (hoverHit) {
+    hoveredSignal = hoverHit.signal;
+    renderSignalPopover(hoverHit, hoverHit.signal);
+  } else {
+    hideSignalPopover();
+  }
   if (isDraggingSpectrum) {
     const dx = ev.clientX - dragStartX;
     pan = Math.max(-0.5, Math.min(0.5, dragStartPan - dx / spectrumCanvas.clientWidth));
@@ -1394,6 +1440,7 @@ maxHoldToggle.addEventListener('change', () => {
 });
 if (debugOverlayToggle) debugOverlayToggle.addEventListener('change', () => {
   showDebugOverlay = debugOverlayToggle.checked;
+  localStorage.setItem('spectre.debugOverlay', showDebugOverlay ? '1' : '0');
   markSpectrumDirty();
   updateHeroMetrics();
 });
@@ -1601,3 +1648,5 @@ setInterval(fetchRecordings, 5000);
 setInterval(loadSignals, 1500);
 setInterval(loadDecoders, 10000);
 
+coders, 10000);
+
diff --git a/web/index.html b/web/index.html
index add056e..1f459d2 100644
--- a/web/index.html
+++ b/web/index.html
@@ -90,6 +90,7 @@
               </span>
             </div>
             <canvas id="spectrum"></canvas>
+            <div class="signal-popover" id="signalPopover" aria-hidden="true"></div>
           </div>
           <div class="viz-card">
             <div class="viz-head"><span class="viz-label">Waterfall</span><span class="viz-hint" id="waterfallMeta">Newest row at top</span></div>
diff --git a/web/style.css b/web/style.css
index 6fba36f..bfc2d66 100644
--- a/web/style.css
+++ b/web/style.css
@@ -213,6 +213,19 @@ button, input, select { font: inherit; }
 .viz-hint { font-family: var(--mono); font-size: 0.58rem; color: var(--text-mute); }
 
 canvas { display: block; width: 100%; height: 100%; border-radius: var(--r-sm); background: #030508; }
+.signal-popover {
+  position: absolute; z-index: 8; pointer-events: none; min-width: 180px;
+  padding: 10px 12px; border-radius: 10px; border: 1px solid var(--line-hi);
+  background: rgba(6, 10, 18, 0.94); box-shadow: 0 18px 50px rgba(0,0,0,0.38);
+  font-size: 0.72rem; color: var(--text); display: none;
+}
+.signal-popover.open { display: block; }
+.signal-popover__title { font-family: var(--mono); font-weight: 700; margin-bottom: 4px; color: var(--accent); }
+.signal-popover__meta { color: var(--text-mute); margin-bottom: 6px; }
+.signal-popover__scores { display: grid; gap: 4px; }
+.signal-popover__row { display: grid; grid-template-columns: 42px 1fr 36px; gap: 6px; align-items: center; font-family: var(--mono); font-size: 0.68rem; }
+.signal-popover__bar { height: 6px; border-radius: 999px; background: rgba(148,163,184,0.14); overflow: hidden; }
+.signal-popover__fill { height: 100%; background: linear-gradient(90deg, rgba(0,255,200,0.72), rgba(0,144,255,0.8)); }
 #spectrum, #waterfall { cursor: crosshair; }
 #spectrum:active { cursor: grabbing; }