diff --git a/Source/Project64/UserInterface/API.js b/Source/Project64/UserInterface/API.js
index bec3727ca..2dc524ece 100644
--- a/Source/Project64/UserInterface/API.js
+++ b/Source/Project64/UserInterface/API.js
@@ -39,6 +39,51 @@ const _regNums = {
     f28: 28, f29: 29, f30: 30, f31: 31
 }
 
+const _gprNames = [
+    'r0', 'at', 'v0', 'v1', 'a0', 'a1', 'a2', 'a3',
+    't0', 't1', 't2', 't3', 't4', 't5', 't6', 't7',
+    's0', 's1', 's2', 's3', 's4', 's5', 's6', 's7',
+    't8', 't9', 'k0', 'k1', 'gp', 'sp', 'fp', 'ra'
+]
+
+const GPR_R0 = (1 << 0)
+const GPR_AT = (1 << 1)
+const GPR_V0 = (1 << 2)
+const GPR_V1 = (1 << 3)
+const GPR_A0 = (1 << 4)
+const GPR_A1 = (1 << 5)
+const GPR_A2 = (1 << 6)
+const GPR_A3 = (1 << 7)
+const GPR_T0 = (1 << 8)
+const GPR_T1 = (1 << 9)
+const GPR_T2 = (1 << 10)
+const GPR_T3 = (1 << 11)
+const GPR_T4 = (1 << 12)
+const GPR_T5 = (1 << 13)
+const GPR_T6 = (1 << 14)
+const GPR_T7 = (1 << 15)
+const GPR_S0 = (1 << 16)
+const GPR_S1 = (1 << 17)
+const GPR_S2 = (1 << 18)
+const GPR_S3 = (1 << 19)
+const GPR_S4 = (1 << 20)
+const GPR_S5 = (1 << 21)
+const GPR_S6 = (1 << 22)
+const GPR_S7 = (1 << 23)
+const GPR_T8 = (1 << 24)
+const GPR_T9 = (1 << 25)
+const GPR_K0 = (1 << 26)
+const GPR_K1 = (1 << 27)
+const GPR_GP = (1 << 28)
+const GPR_SP = (1 << 29)
+const GPR_FP = (1 << 30)
+const GPR_RA = (1 << 31) >>> 0
+
+const GPR_ANY_ARG = (GPR_A0 | GPR_A1 | GPR_A2 | GPR_A3)
+const GPR_ANY_TEMP = (GPR_T0 | GPR_T1 | GPR_T2 | GPR_T3 | GPR_T4 | GPR_T5 | GPR_T6 | GPR_T7 | GPR_T8 | GPR_T9)
+const GPR_ANY_SAVE = (GPR_S0 | GPR_S1 | GPR_S2 | GPR_S3 | GPR_S4 | GPR_S5 | GPR_S6 | GPR_S7)
+const GPR_ANY = (GPR_R0 | GPR_AT | GPR_V0 | GPR_V1 | GPR_ANY_ARG | GPR_ANY_TEMP | GPR_ANY_SAVE | GPR_K0 | GPR_K1 | GPR_GP | GPR_SP | GPR_FP | GPR_RA) >>> 0
+
 function AddressRange(start, end)
 {
     this.start = start >>> 0
@@ -56,6 +101,17 @@ const ADDR_ANY_RDRAM_UNC = new AddressRange(0xA0000000, 0xA0800000)
 const ADDR_ANY_CART_ROM = new AddressRange(0x90000000, 0x96000000)
 const ADDR_ANY_CART_ROM_UNC = new AddressRange(0xB0000000, 0xB6000000)
 
+const asm = {
+    gprname: function(num)
+    {
+        if(num in _gprNames)
+        {
+            return _gprNames[num]
+        }
+        return ""
+    }
+}
+
 const fs = {
     open: function(path, mode)
     {
@@ -331,7 +387,25 @@ const events = (function()
             }
 
             this._stashCallback(callback);
-            return _native.addCallback('onopcode', callback, start, end, value, mask)
+            return _native.addCallback('opcode', callback, start, end, value, mask)
+        },
+        ongprvalue: function(addr, registers, value, callback)
+        {
+            var start = 0;
+            var end = 0;
+
+            if(typeof(addr) == "object")
+            {
+                start = addr.start;
+                end = addr.end;
+            }
+            else if(typeof(addr) == "number")
+            {
+                start = addr;
+            }
+
+            this._stashCallback(callback);
+            return _native.addCallback('gprvalue', callback, start, end, registers, value)
         },
         onread: function(addr, callback)
         {
@@ -754,7 +828,6 @@ function alert(text, caption){
     _native.msgBox(text, caption)
 }
 
-
 function Socket(fd)
 {
     var connected = false;
diff --git a/Source/Project64/UserInterface/Debugger/Debugger.cpp b/Source/Project64/UserInterface/Debugger/Debugger.cpp
index cc5a2944b..747e7f0f6 100644
--- a/Source/Project64/UserInterface/Debugger/Debugger.cpp
+++ b/Source/Project64/UserInterface/Debugger/Debugger.cpp
@@ -576,8 +576,9 @@ void CDebuggerUI::CPUStepStarted()
     uint32_t PROGRAM_COUNTER = g_Reg->m_PROGRAM_COUNTER;
     uint32_t JumpToLocation = R4300iOp::m_JumpToLocation;
 
-    m_ScriptSystem->HookCPUExec()->InvokeByParamInRange(PROGRAM_COUNTER);
-    m_ScriptSystem->HookCPUExecOpcode()->InvokeByParamInRangeWithMaskedValue(PROGRAM_COUNTER, R4300iOp::m_Opcode.Hex);
+    m_ScriptSystem->HookCPUExec()->InvokeByAddressInRange(PROGRAM_COUNTER);
+    m_ScriptSystem->HookCPUExecOpcode()->InvokeByAddressInRange_MaskedOpcode(PROGRAM_COUNTER, R4300iOp::m_Opcode.Hex);
+	m_ScriptSystem->HookCPUGPRValue()->InvokeByAddressInRange_GPRValue(PROGRAM_COUNTER);
 
     // Memory breakpoints
 
@@ -589,11 +590,11 @@ void CDebuggerUI::CPUStepStarted()
 
         if (opInfo.IsLoadCommand()) // Read instructions
         {
-            m_ScriptSystem->HookCPURead()->InvokeByParamInRange(memoryAddress);
+            m_ScriptSystem->HookCPURead()->InvokeByAddressInRange(memoryAddress);
         }
         else // Write instructions
         {
-            m_ScriptSystem->HookCPUWrite()->InvokeByParamInRange(memoryAddress);
+            m_ScriptSystem->HookCPUWrite()->InvokeByAddressInRange(memoryAddress);
 
             // Catch cart -> rdram dma
             if (memoryAddress == 0xA460000C) // PI_WR_LEN_REG
diff --git a/Source/Project64/UserInterface/Debugger/ScriptHook.cpp b/Source/Project64/UserInterface/Debugger/ScriptHook.cpp
index 2d0b8ed6f..fecf459a6 100644
--- a/Source/Project64/UserInterface/Debugger/ScriptHook.cpp
+++ b/Source/Project64/UserInterface/Debugger/ScriptHook.cpp
@@ -46,35 +46,65 @@ void CScriptHook::InvokeByParam(uint32_t param)
     }
 }
 
-void CScriptHook::InvokeByParamInRange(uint32_t param)
+void CScriptHook::InvokeByAddressInRange(uint32_t address)
 {
     int nCallbacks = m_Callbacks.size();
     for (int i = 0; i < nCallbacks; i++)
     {
-        if (param == m_Callbacks[i].param || (param >= m_Callbacks[i].param && param < m_Callbacks[i].param2))
+        if (address == m_Callbacks[i].param || (address >= m_Callbacks[i].param && address < m_Callbacks[i].param2))
         {
-            m_Callbacks[i].scriptInstance->Invoke(m_Callbacks[i].heapptr, param);
+            m_Callbacks[i].scriptInstance->Invoke(m_Callbacks[i].heapptr, address);
             return;
         }
     }
 }
 
-void CScriptHook::InvokeByParamInRangeWithMaskedValue(uint32_t param, uint32_t value)
+void CScriptHook::InvokeByAddressInRange_MaskedOpcode(uint32_t pc, uint32_t opcode)
 {
     int nCallbacks = m_Callbacks.size();
     for (int i = 0; i < nCallbacks; i++)
     {
-        if (param == m_Callbacks[i].param || (param >= m_Callbacks[i].param && param < m_Callbacks[i].param2))
+        if (pc == m_Callbacks[i].param || (pc >= m_Callbacks[i].param && pc < m_Callbacks[i].param2))
         {
-            if ((m_Callbacks[i].param3 & m_Callbacks[i].param4) == (value & m_Callbacks[i].param4))
+            if ((m_Callbacks[i].param3 & m_Callbacks[i].param4) == (opcode & m_Callbacks[i].param4))
             {
-                m_Callbacks[i].scriptInstance->Invoke(m_Callbacks[i].heapptr, param);
+                m_Callbacks[i].scriptInstance->Invoke(m_Callbacks[i].heapptr, pc);
                 return;
             }
         }
     }
 }
 
+void CScriptHook::InvokeByAddressInRange_GPRValue(uint32_t pc)
+{
+	int nCallbacks = m_Callbacks.size();
+
+	for (int i = 0; i < nCallbacks; i++)
+	{
+		uint32_t startAddress = m_Callbacks[i].param;
+		uint32_t endAddress = m_Callbacks[i].param2;
+		uint32_t registers = m_Callbacks[i].param3;
+		uint32_t value = m_Callbacks[i].param4;
+
+		if (!(pc == startAddress || (pc >= startAddress && pc < endAddress)))
+		{
+			continue;
+		}
+
+		for (int nReg = 0; nReg < 32; nReg++)
+		{
+			if (registers & (1 << nReg))
+			{
+				if (value == g_Reg->m_GPR[nReg].UW[0])
+				{
+					m_Callbacks[i].scriptInstance->Invoke2(m_Callbacks[i].heapptr, pc, nReg);
+                    break;
+				}
+			}
+		}
+	}
+}
+
 void CScriptHook::InvokeAll()
 {
     int nCallbacks = m_Callbacks.size();
diff --git a/Source/Project64/UserInterface/Debugger/ScriptHook.h b/Source/Project64/UserInterface/Debugger/ScriptHook.h
index f82de1968..4b111e385 100644
--- a/Source/Project64/UserInterface/Debugger/ScriptHook.h
+++ b/Source/Project64/UserInterface/Debugger/ScriptHook.h
@@ -33,9 +33,10 @@ public:
     void InvokeById(int callbackId);
     void InvokeByParam(uint32_t param);
     /* invoke if param >= cb.param && param < cb.param2*/
-    void InvokeByParamInRange(uint32_t param);
+    void InvokeByAddressInRange(uint32_t address);
     /* invoke if param >= cb.param && param < cb.param2 && (value & cb.param4) == cb.param3 */
-    void InvokeByParamInRangeWithMaskedValue(uint32_t param, uint32_t value);
+    void InvokeByAddressInRange_MaskedOpcode(uint32_t pc, uint32_t value);
+	void InvokeByAddressInRange_GPRValue(uint32_t pc);
     void RemoveById(int callbackId);
     void RemoveByParam(uint32_t tag);
     void RemoveByInstance(CScriptInstance* scriptInstance);
diff --git a/Source/Project64/UserInterface/Debugger/ScriptInstance.cpp b/Source/Project64/UserInterface/Debugger/ScriptInstance.cpp
index d04276c7a..9cb311665 100644
--- a/Source/Project64/UserInterface/Debugger/ScriptInstance.cpp
+++ b/Source/Project64/UserInterface/Debugger/ScriptInstance.cpp
@@ -577,6 +577,26 @@ void CScriptInstance::Invoke(void* heapptr, uint32_t param)
     LeaveCriticalSection(&m_CriticalSection);
 }
 
+void CScriptInstance::Invoke2(void* heapptr, uint32_t param, uint32_t param2)
+{
+    EnterCriticalSection(&m_CriticalSection);
+    duk_push_heapptr(m_Ctx, heapptr);
+    duk_push_uint(m_Ctx, param);
+    duk_push_uint(m_Ctx, param2);
+
+    duk_int_t status = duk_pcall(m_Ctx, 2);
+
+    if (status != DUK_EXEC_SUCCESS)
+    {
+        const char* errorText = duk_safe_to_string(m_Ctx, -1);
+        m_Debugger->Debug_LogScriptsWindow(errorText);
+        m_Debugger->Debug_LogScriptsWindow("\r\n");
+    }
+
+    duk_pop(m_Ctx);
+    LeaveCriticalSection(&m_CriticalSection);
+}
+
 void CScriptInstance::QueueAPC(PAPCFUNC userProc, ULONG_PTR param)
 {
     if (m_hThread != NULL)
diff --git a/Source/Project64/UserInterface/Debugger/ScriptInstance.h b/Source/Project64/UserInterface/Debugger/ScriptInstance.h
index 48cd1eb44..afc926daa 100644
--- a/Source/Project64/UserInterface/Debugger/ScriptInstance.h
+++ b/Source/Project64/UserInterface/Debugger/ScriptInstance.h
@@ -68,6 +68,7 @@ public:
     void Start(char* path);
     void ForceStop();
     void Invoke(void* heapptr, uint32_t param = 0);
+    void Invoke2(void* heapptr, uint32_t param = 0, uint32_t param2 = 0);
     INSTANCE_STATE GetState();
 
     friend class PendingEval;
diff --git a/Source/Project64/UserInterface/Debugger/ScriptSystem.cpp b/Source/Project64/UserInterface/Debugger/ScriptSystem.cpp
index cf4bb70c0..db7c34c42 100644
--- a/Source/Project64/UserInterface/Debugger/ScriptSystem.cpp
+++ b/Source/Project64/UserInterface/Debugger/ScriptSystem.cpp
@@ -28,12 +28,14 @@ CScriptSystem::CScriptSystem(CDebuggerUI* debugger)
     m_HookCPUExecOpcode = new CScriptHook(this);
     m_HookCPURead = new CScriptHook(this);
     m_HookCPUWrite = new CScriptHook(this);
+    m_HookCPUGPRValue = new CScriptHook(this);
     m_HookFrameDrawn = new CScriptHook(this);
 
     RegisterHook("exec", m_HookCPUExec);
     RegisterHook("read", m_HookCPURead);
     RegisterHook("write", m_HookCPUWrite);
-    RegisterHook("onopcode", m_HookCPUExecOpcode);
+    RegisterHook("opcode", m_HookCPUExecOpcode);
+	RegisterHook("gprvalue", m_HookCPUGPRValue);
     RegisterHook("draw", m_HookFrameDrawn);
 
     HMODULE hInst = GetModuleHandle(NULL);
diff --git a/Source/Project64/UserInterface/Debugger/ScriptSystem.h b/Source/Project64/UserInterface/Debugger/ScriptSystem.h
index ea2625c44..52d872ccf 100644
--- a/Source/Project64/UserInterface/Debugger/ScriptSystem.h
+++ b/Source/Project64/UserInterface/Debugger/ScriptSystem.h
@@ -55,7 +55,7 @@ private:
     CScriptHook* m_HookCPURead;
     CScriptHook* m_HookCPUWrite;
     CScriptHook* m_HookCPUExecOpcode;
-
+	CScriptHook* m_HookCPUGPRValue;
     CScriptHook* m_HookFrameDrawn;
 
     void RegisterHook(const char* hookId, CScriptHook* cbList); // associate string id with callback list
@@ -126,6 +126,11 @@ public:
         return m_HookCPUExecOpcode;
     }
 
+	CScriptHook* HookCPUGPRValue()
+	{
+		return m_HookCPUGPRValue;
+	}
+
     CScriptHook* HookFrameDrawn()
     {
         return m_HookFrameDrawn;
diff --git a/apidoc.htm b/apidoc.htm
index 0220bf90e..57f7a1c64 100644
--- a/apidoc.htm
+++ b/apidoc.htm
@@ -98,6 +98,7 @@ span.tag2 {
 		<a href="#rom">rom</a><br>
 		<a href="#events">events</a><br>
 		<a href="#debug">debug</a><br>
+		<a href="#asm">asm</a><br>
 		<a href="#console">console</a><br>
 		<a href="#fs">fs</a><br>
 		<a href="#fs.Stats">fs.Stats</a><br>
@@ -336,7 +337,7 @@ events.onwrite(ADDR_ANY_CART_ROM_UNC, function(addr)
 		<span class="tag">interpreter mode only</span>
 		<div class="propertyname">events.onopcode(address, opcode, callback)</div>
 		<div class="propertydesc">
-			Adds a CPU executions callback for a virtual address or <a href="#AddressRange">AddressRange</a> and returns a callback ID.
+			Adds a CPU execution callback for a virtual address or <a href="#AddressRange">AddressRange</a> and returns a callback ID.
 			<span class="snip">callback</span> will be invoked at the beginning of a CPU step if the program counter is at <span class="snip">address</span> and <span class="snip">opcode</span> is equal to the opcode to be executed.
 			<span class="snip">callback</span> receives the program counter address at which the event is fired.
 			<pre class="example">
@@ -354,7 +355,7 @@ events.onopcode(ADDR_ANY, JR_RA, function(pc)
 		<span class="tag">interpreter mode only</span>
 		<div class="propertyname">events.onopcode(address, opcode, mask, callback)</div>
 		<div class="propertydesc">
-			Adds a CPU executions callback for a virtual address or <a href="#AddressRange">AddressRange</a> and returns a callback ID.
+			Adds a CPU execution callback for a virtual address or <a href="#AddressRange">AddressRange</a> and returns a callback ID.
 			<span class="snip">callback</span> will be invoked at the beginning of a CPU step if the program counter is at <span class="snip">address</span> and <span class="snip">opcode</span> is equal to the opcode to be executed ANDed with <span class="snip">mask</span>.
 			<span class="snip">callback</span> receives the program counter address at which the event is fired.
 			<pre class="example">
@@ -379,6 +380,42 @@ events.onopcode(ADDR_ANY, JAL, NO_TARGET, function(pc)
 </pre>
 			</div>
 		</div>
+	<div class="property">
+		<span class="tag2">emulation thread</span>
+		<span class="tag">interpreter mode only</span>
+		<div class="propertyname">events.ongprvalue(address, registers, value, callback)</div>
+		<div class="propertydesc">
+			Adds a CPU execution callback for a virtual address or <a href="#AddressRange">AddressRange</a> and returns a callback ID.
+			<span class="snip">callback</span> will be invoked at the beginning of a CPU step if the program counter is at <span class="snip">address</span> and the lower 32 bits of the general purpose registers specified by <span class="snip">registers</span> are equal to <span class="snip">value</span>.
+			<span class="snip">callback</span> receives the program counter address at which the event is fired, and the index of the first register that contains the value.
+			<pre class="example">
+events.ongprvalue(ADDR_ANY, GPR_ANY, 0x49533634, function(pc, reg)
+{
+    // log pc whenever any general purpose register contains 0x49533634
+    console.log(pc.hex(), asm.gprname(reg))
+})
+</pre>
+	<pre class="example">
+events.ongprvalue(ADDR_ANY, GPR_A0 | GPR_A1, 0x00001234, function(pc, reg)
+{
+    // log pc whenever A0 or A1 contains 0x00001234
+    console.log(pc.hex(), asm.gprname(reg))
+})
+</pre>
+		Valid registers:
+		<pre style="font-size: 13px;">
+GPR_R0 GPR_AT GPR_V0 GPR_V1 GPR_A0 GPR_A1 GPR_A2 GPR_A3
+GPR_T0 GPR_T1 GPR_T2 GPR_T3 GPR_T4 GPR_T5 GPR_T6 GPR_T7
+GPR_S0 GPR_S1 GPR_S2 GPR_S3 GPR_S4 GPR_S5 GPR_S6 GPR_S7
+GPR_T8 GPR_T9 GPR_K0 GPR_K1 GPR_GP GPR_SP GPR_FP GPR_RA
+
+GPR_ANY_ARG  -- Any of the 'A' registers
+GPR_ANY_TEMP -- Any of the 'T' registers
+GPR_ANY_SAVE -- Any of the 'S' registers
+GPR_ANY      -- Any register
+</pre>
+		</div>
+	</div>
 	<div class="property">
 		<span class="tag2">emulation thread</span>
 		<div class="propertyname">events.ondraw(callback)</div>
@@ -437,6 +474,19 @@ events.onexec(0x802CB1C0, function()
 	</div>
 </div>
 
+<div class="panel" id="asm">
+		<div class="classname">asm</div>
+		<div class="property">
+			<div class="propertyname">asm.gprname(regIndex)</div>
+			<div class="propertydesc">
+				Returns the name of the general purpose register specified by <span class="snip">regIndex</span>.
+				<pre class="example">
+asm.gprname(4) // 'a0'
+</pre>
+			</div>
+		</div>
+	</div>
+
 <div class="panel" id="fs">
 	<div class="classname">fs</div>
 	<div class="property">