--- a/rts/Sim/Units/Scripts/UnitScript.cpp
+++ b/rts/Sim/Units/Scripts/UnitScript.cpp
@@ -212,6 +212,9 @@
 
 	// clear doneAnims here to preserve them for DumpState
 	doneAnims.clear();
+#ifdef WEBBAR_SYNC_TRACE
+	webbarTraceAnims.clear();
+#endif
 
 	for (auto& ai : anims) {
 		LocalModelPiece& lmp = *pieces[ai.piece];
@@ -223,6 +226,9 @@
 
 		// checksum all anims (live + done)
 		checksum = spring::LiteHash(ai, checksum);
+#ifdef WEBBAR_SYNC_TRACE
+		{ std::array<unsigned char, sizeof(AnimInfo)> raw; memcpy(raw.data(), &ai, sizeof(AnimInfo)); webbarTraceAnims.push_back(raw); }
+#endif
 	}
 
 	spring::VectorEraseIfAll(anims, [](const auto& ai) { return ai.done; });
--- a/rts/Sim/Units/Scripts/UnitScript.h
+++ b/rts/Sim/Units/Scripts/UnitScript.h
@@ -117,6 +117,9 @@
 	const CUnit* GetUnit() const { return unit; }
 
 	auto GetAnimArrayChecksum() const { return checksum; }
+#ifdef WEBBAR_SYNC_TRACE
+	std::vector<std::array<unsigned char, sizeof(AnimInfo)>> webbarTraceAnims;
+#endif
 	void TickAllAnims(int tickRate);
 	bool TickAnimFinished();
 	// note: must copy-and-set here (LMP dirty flag, etc)
--- a/rts/Sim/Units/Scripts/UnitScriptEngine.cpp
+++ b/rts/Sim/Units/Scripts/UnitScriptEngine.cpp
@@ -150,6 +150,9 @@
 			currentScript = animating[i];
 			// deal with synced checksum here, before animating is possibly popped below
 			cs = spring::hash_combine(currentScript->GetAnimArrayChecksum(), cs);
+#ifdef WEBBAR_SYNC_TRACE
+			{ const uint32_t scs = currentScript->GetAnimArrayChecksum(); CSyncChecker::TraceBytes("S", currentScript->GetUnit() ? currentScript->GetUnit()->id : -1, &scs, sizeof(scs)); for (const auto& raw : currentScript->webbarTraceAnims) CSyncChecker::TraceBytes("A", currentScript->GetUnit() ? currentScript->GetUnit()->id : -1, raw.data(), raw.size()); }
+#endif
 
 			if (!currentScript->TickAnimFinished()) {
 				animating[i] = animating.back();
--- a/rts/System/Sync/SyncChecker.cpp
+++ b/rts/System/Sync/SyncChecker.cpp
@@ -14,6 +14,31 @@
 unsigned CSyncChecker::g_prevChecksum;
 int CSyncChecker::inSyncedCode;
 
+#ifdef WEBBAR_SYNC_TRACE
+#include <cstdio>
+#include <cstdlib>
+#include "Sim/Misc/GlobalSynced.h"
+// WebBAR sync trace (diagnostic only): WEBBAR_SYNC_TRACE=from:to logs every checksum input of those frames.
+const char* CSyncChecker::traceMsg = "";
+static FILE* webbarTraceFile = nullptr; static int webbarTraceFrom = -1, webbarTraceTo = -1, webbarTraceFrame = -2; static bool webbarTraceInit = false; static unsigned webbarTraceIdx = 0;
+void* CSyncChecker::TraceFile() {
+	if (!webbarTraceInit) { webbarTraceInit = true; const char* r = getenv("WEBBAR_SYNC_TRACE"); if (r && sscanf(r, "%d:%d", &webbarTraceFrom, &webbarTraceTo) == 2) { const char* f = getenv("WEBBAR_SYNC_TRACE_FILE"); webbarTraceFile = fopen(f ? f : "sync-trace.txt", "w"); } }
+	if (webbarTraceFile == nullptr || gs == nullptr) return nullptr;
+	const int fr = gs->frameNum; if (fr < webbarTraceFrom || fr > webbarTraceTo) { if (fr > webbarTraceTo) fflush(webbarTraceFile); return nullptr; }
+	if (fr != webbarTraceFrame) { webbarTraceFrame = fr; webbarTraceIdx = 0; fprintf(webbarTraceFile, "F %d\n", fr); fflush(webbarTraceFile); }
+	return webbarTraceFile;
+}
+void CSyncChecker::TraceBytes(const char* tag, int id, const void* p, unsigned size) {
+	FILE* f = static_cast<FILE*>(TraceFile()); if (f == nullptr) return;
+	fprintf(f, "%s %d %u ", tag, id, size); for (unsigned i = 0; i < size; i++) fprintf(f, "%02x", static_cast<const unsigned char*>(p)[i]); fprintf(f, "\n");
+}
+static void WebbarTraceSync(const void* p, unsigned size, unsigned cs) {
+	FILE* f = static_cast<FILE*>(CSyncChecker::TraceFile()); if (f == nullptr) return;
+	fprintf(f, "%u %s %u ", webbarTraceIdx++, CSyncChecker::traceMsg ? CSyncChecker::traceMsg : "?", size); for (unsigned i = 0; i < size; i++) fprintf(f, "%02x", static_cast<const unsigned char*>(p)[i]); fprintf(f, " %08x\n", cs);
+	CSyncChecker::traceMsg = "";
+}
+#endif
+
 void CSyncChecker::NewFrame()
 {
 	g_checksum = 0xfade1eaf;
@@ -34,6 +59,9 @@
 	debugSyncCheckThreading();
 #endif
 	g_checksum = spring::hash_combine(val, g_checksum);
+#ifdef WEBBAR_SYNC_TRACE
+	WebbarTraceSync(&val, sizeof(val), g_checksum);
+#endif
 	//LOG("[Sync::Checker] chksum=%u\n", g_checksum);
 
 #ifdef SYNC_HISTORY
@@ -50,6 +78,9 @@
 	// most common cases first, make it easy for compiler to optimize for it
 	// simple xor is not enough to detect multiple zeroes, e.g.
 	g_checksum = spring::LiteHash(p, size, g_checksum);
+#ifdef WEBBAR_SYNC_TRACE
+	WebbarTraceSync(p, size, g_checksum);
+#endif
 	//LOG("[Sync::Checker] chksum=%u\n", g_checksum);
 
 #ifdef SYNC_HISTORY
--- a/rts/System/Sync/SyncChecker.h
+++ b/rts/System/Sync/SyncChecker.h
@@ -37,6 +37,11 @@
 		static void debugSyncCheckThreading();
 		static void Sync(uint32_t val);
 		static void Sync(const void* p, unsigned size);
+		#ifdef WEBBAR_SYNC_TRACE
+		static const char* traceMsg;
+		static void* TraceFile();
+		static void TraceBytes(const char* tag, int id, const void* p, unsigned size);
+		#endif
 		#ifdef SYNC_HISTORY
 		static std::tuple<unsigned, unsigned, unsigned*> GetFrameHistory(unsigned rewindFrames);
 		static std::pair<unsigned, unsigned*> GetHistory() { return std::make_pair(nextHistoryIndex, logs.data()); };
--- a/rts/System/Sync/SyncedPrimitiveBase.h
+++ b/rts/System/Sync/SyncedPrimitiveBase.h
@@ -45,6 +45,9 @@
 		AssertDebugger(p, size, msg);
 #ifdef SYNCCHECK
 		assert(CSyncChecker::InSyncedCode());
+	#ifdef WEBBAR_SYNC_TRACE
+		CSyncChecker::traceMsg = msg;
+	#endif
 		CSyncChecker::Sync(p, size);
 	#ifdef TRACE_SYNC
 		unsigned int crc = CSyncChecker::GetChecksum();
@@ -57,6 +60,9 @@
 		AssertDebugger(val, msg);
 #ifdef SYNCCHECK
 		assert(CSyncChecker::InSyncedCode());
+	#ifdef WEBBAR_SYNC_TRACE
+		CSyncChecker::traceMsg = msg;
+	#endif
 		CSyncChecker::Sync(val);
 	#ifdef TRACE_SYNC
 		unsigned int crc = CSyncChecker::GetChecksum();