diff --git a/app/tools/diag.sh b/app/tools/diag.sh
new file mode 100755
index 0000000..8f79c32
--- /dev/null
+++ b/app/tools/diag.sh
@@ -0,0 +1,39 @@
+#!/bin/bash
+# Church Translate — one-shot diagnostic for "it is behind / in the red".
+# Read-only: reads the log and asks the running app for its status. Changes nothing.
+L="$HOME/Library/Application Support/Church Translate/data/logs/app.log"
+C="$HOME/Library/Application Support/Church Translate/data/config.json"
+
+echo "=== MACHINE ==="
+system_profiler SPHardwareDataType 2>/dev/null | grep -E "Model Name|Chip|Total Number of Cores|Memory:" | sed 's/^ */  /'
+echo "  macOS $(sw_vers -productVersion)"
+
+echo
+echo "=== MEMORY PRESSURE / SWAP ==="
+memory_pressure 2>/dev/null | grep -Ei "free percentage|pageouts" | sed 's/^/  /'
+sysctl -n vm.swapusage 2>/dev/null | sed 's/^/  swap: /'
+
+echo
+echo "=== WHAT THE APP CHOSE AT STARTUP ==="
+grep -E "GPU features \(speech\)|no GPU acceleration|no fp16|loading the speech model|loading the translation model|speech model ready|translation model ready|models could not load" "$L" 2>/dev/null | tail -8 | sed 's/^/  /'
+
+echo
+echo "=== THROUGHPUT — is it slower than people talk? ==="
+echo "  slow-sentence events (>4s): $(grep -c 'slow sentence' "$L" 2>/dev/null)"
+grep "slow sentence" "$L" 2>/dev/null | tail -12 | sed 's/^/  /'
+grep -E "stepping down to a lighter" "$L" 2>/dev/null | tail -3 | sed 's/^/  /'
+
+echo
+echo "=== THE RED CONDITION ==="
+echo "  caption-only events: $(grep -c 'caption only' "$L" 2>/dev/null)"
+grep -E "caption only|stale — caption only" "$L" 2>/dev/null | tail -6 | sed 's/^/  /'
+
+echo
+echo "=== LIVE STATUS ==="
+TOK=$(grep -o '"controlToken"[[:space:]]*:[[:space:]]*"[^"]*"' "$C" 2>/dev/null | sed 's/.*"\([^"]*\)"$/\1/')
+curl -s -m 5 "http://127.0.0.1:3100/api/control/status?key=$TOK" 2>/dev/null | head -c 1500
+echo
+
+echo
+echo "=== RECENT ERRORS ==="
+grep "\[app\] err" "$L" 2>/dev/null | grep -v "natural voice fell back" | tail -12 | sed 's/^/  /'