--- a/rts/Game/WebbarBrowser.h
+++ b/rts/Game/WebbarBrowser.h
@@ -58,6 +58,7 @@
 }
 
 #include "WebbarResurrection.h"
+#include "WebbarNano.h"
 #include "WebbarSkirmish.h"
 #include "WebbarWorld.h"
 #include "WebbarTerrain.h"
@@ -80,7 +81,7 @@
 	if (!catalogSent) {
 		catalogSent = true;
 		if (std::getenv("WEBBAR_NETWORK") != nullptr) { static WebbarNetworkResult result; }
-		MAIN_THREAD_EM_ASM({ if (Module['webbarProtocol']) Module['webbarProtocol'](8, 15 /* area restore | shield state | owner cloak | resurrection */); });
+		MAIN_THREAD_EM_ASM({ if (Module['webbarProtocol']) Module['webbarProtocol'](8, 31 /* restore | shields | cloak | resurrection | native work effects */); });
 		MAIN_THREAD_EM_ASM({
 			if (Module['webbarIdentity']) Module['webbarIdentity']($0, $1, $2, $3);
 		}, gu->myPlayerNum, gu->myTeam, gu->myAllyTeam, int(gu->spectating));
@@ -454,6 +455,7 @@
 	}
 	if (browser) {
 		if (std::getenv("WEBBAR_PLAYABLE") != nullptr) {
+			WebbarNano::Publish();
 			PublishWebbarTerrain();
 			PublishWebbarPlayState();
 			PublishWebbarPoses();
--- a/rts/Sim/Units/UnitTypes/Builder.cpp
+++ b/rts/Sim/Units/UnitTypes/Builder.cpp
@@ -3,6 +3,9 @@
 #include <assert.h>
 #include <algorithm>
 #include "Builder.h"
+#if defined(__EMSCRIPTEN__)
+#include "Game/WebbarNano.h"
+#endif
 #include "Building.h"
 #include "Game/GameHelper.h"
 #include "Game/GlobalUnsynced.h"
@@ -998,6 +1001,15 @@
 	const float3 relNanoFirePos = localModel.GetRawPiecePos(modelNanoPiece);
 	const float3 nanoPos = this->GetObjectSpacePos(relNanoFirePos);
 
+	#if defined(__EMSCRIPTEN__)
+	if (curResurrect != nullptr) WebbarNano::Emit(this, nanoPos, goal, radius, inverse, 3, nullptr, curResurrect);
+	else if (curReclaim != nullptr) {
+		if (reclaimingUnit) WebbarNano::Emit(this, nanoPos, goal, radius, inverse, 4, static_cast<const CUnit*>(curReclaim));
+		else WebbarNano::Emit(this, nanoPos, goal, radius, inverse, 4, nullptr, static_cast<const CFeature*>(curReclaim));
+	} else if (curCapture != nullptr) WebbarNano::Emit(this, nanoPos, goal, radius, inverse, 5, curCapture);
+	else if (curBuild != nullptr) WebbarNano::Emit(this, nanoPos, goal, radius, inverse, curBuild->beingBuilt ? 1 : 2, curBuild);
+	#endif
+
 	// unsynced
 	projectileHandler.AddNanoParticle(nanoPos, goal, unitDef, team, radius, inverse, highPriority);
 }
--- a/rts/Sim/Units/UnitTypes/Factory.cpp
+++ b/rts/Sim/Units/UnitTypes/Factory.cpp
@@ -2,6 +2,9 @@
 
 
 #include "Factory.h"
+#if defined(__EMSCRIPTEN__)
+#include "Game/WebbarNano.h"
+#endif
 #include "Game/GameHelper.h"
 #include "Game/WaitCommandsAI.h"
 #include "Map/Ground.h"
@@ -546,6 +549,10 @@
 	const float3 relNanoFirePos = localModel.GetRawPiecePos(modelNanoPiece);
 	const float3 nanoPos = this->GetObjectSpacePos(relNanoFirePos);
 
+	#if defined(__EMSCRIPTEN__)
+	WebbarNano::Emit(this, nanoPos, curBuild->midPos, curBuild->radius * 0.5f, false, 1, curBuild);
+	#endif
+
 	// unsynced
 	projectileHandler.AddNanoParticle(nanoPos, curBuild->midPos, unitDef, team, highPriority);
 }
--- /dev/null
+++ b/rts/Game/WebbarNano.h
@@ -0,0 +1,48 @@
+/* This file is part of the Spring engine (GPL v2 or later), see LICENSE.html */
+#pragma once
+
+#include <algorithm>
+#include <cstring>
+#include <vector>
+#include <emscripten.h>
+#include "Game/GlobalUnsynced.h"
+#include "Sim/Misc/GlobalSynced.h"
+#include "Sim/Misc/LosHandler.h"
+#include "Sim/Features/Feature.h"
+#include "Sim/Units/Unit.h"
+#include "Sim/Units/UnitDef.h"
+
+// Browser-only observation of native spray calls. Never query a script, move a
+// unit, consume RNG, or change whether native build power is applied.
+namespace WebbarNano {
+struct Record {
+	uint32_t id, frame, source, target, kind, flags;
+	float start[3], end[3], radius, color[3];
+};
+static_assert(sizeof(Record) == 64);
+inline std::vector<Record> pending;
+inline uint32_t nextId = 0, dropped = 0;
+
+inline void Emit(const CUnit* source, const float3& start, const float3& end, float radius, bool inverse, uint32_t kind, const CUnit* unit, const CFeature* feature = nullptr)
+{
+	// Initial scope: local player's work only, with a currently visible target.
+	if (!source->unitDef->showNanoSpray || source->isDead || source->team != gu->myTeam) return;
+	if (unit != nullptr && (unit->isDead || (unit->team != gu->myTeam && !unit->IsInLosForAllyTeam(gu->myAllyTeam)))) return;
+	if (feature != nullptr && (feature->deleteMe || !losHandler->InLos(feature->pos, gu->myAllyTeam))) return;
+	if (unit == nullptr && feature == nullptr) return;
+	if (pending.size() >= 1024) { ++dropped; return; }
+	const float3 color = source->unitDef->nanoColor;
+	pending.push_back({++nextId, uint32_t(gs->frameNum), uint32_t(source->id), uint32_t(unit ? unit->id : feature->id), kind, uint32_t(inverse) | (feature ? 2u : 0u),
+		{start.x, start.y, start.z}, {end.x, end.y, end.z}, radius, {color.x, color.y, color.z}});
+}
+
+inline void Publish()
+{
+	const uint32_t header[] = {0x314e4257, uint32_t(gs->frameNum), uint32_t(pending.size()), dropped};
+	std::vector<uint8_t> packet(sizeof(header) + pending.size() * sizeof(Record));
+	std::memcpy(packet.data(), header, sizeof(header));
+	if (!pending.empty()) std::memcpy(packet.data() + sizeof(header), pending.data(), pending.size() * sizeof(Record));
+	MAIN_THREAD_EM_ASM({ if (Module['webbarNano']) Module['webbarNano'](HEAPU8.slice($0, $0 + $1).buffer); }, packet.data(), packet.size());
+	pending.clear(); dropped = 0;
+}
+}