diff --git a/tools/callgrind.c b/tools/callgrind.c
new file mode 100644
index 0000000..35ae142
--- /dev/null
+++ b/tools/callgrind.c
@@ -0,0 +1,330 @@
+/**
+ * @brief Function call tracing tool
+ * @file tools/callgrind.c
+ * @author K. Lange <klange@toaruos.org>
+ *
+ * Generates cachegrind/callgrind trace files while running scripts.
+ *
+ * Traces include per-line instruction execution counts and per-function
+ * (as well as per-call) wall clock timing information.
+ *
+ * Collecting instruction counts can be quite slow, so expect this to
+ * increase runtime by as much as ~25×, depending on the code.
+ */
+#include <stdio.h>
+#include <unistd.h>
+#include <time.h>
+#include <errno.h>
+#include <kuroko/kuroko.h>
+#include <kuroko/vm.h>
+#include <kuroko/debug.h>
+#include <kuroko/util.h>
+
+#include "common.h"
+
+extern KrkValue krk_operator_add (KrkValue a, KrkValue b);
+extern KrkValue krk_operator_sub (KrkValue a, KrkValue b);
+
+static int usage(char * argv[]) {
+	fprintf(stderr, "usage: %s [FILE] [args...]\n", argv[0]);
+	return 1;
+}
+
+static KrkValue lineCache; /* {sourceCO: {line: count}} */
+static KrkValue callCache; /* {sourceCO: {(codeobject,targetLine,sourceLine): [calls,instructions,time]}} */
+static KrkValue timeCache; /* {sourceCO: time} */
+
+static size_t lastFrameCount = 0;   /* Previously seen frame count, to track function entry/exit */
+static size_t instrCounter = 0;     /* Total counter of executed instructions */
+static size_t functionsEntered = 0; /* Number of function entries seen */
+
+/**
+ * @brief Calculate time difference as string.
+ *
+ * Calculates the number of nanoseconds since @p in_time and formats
+ * the result as a string which can then be parsed into a @c long.
+ *
+ * @param in_time Start time to calculate from.
+ * @param buf     String buffer to write into.
+ */
+static void time_diff(struct timespec in_time, char * buf) {
+	struct timespec outTime, diff;
+	clock_gettime(CLOCK_MONOTONIC, &outTime);
+	diff.tv_sec  = outTime.tv_sec  - in_time.tv_sec;
+	diff.tv_nsec = outTime.tv_nsec - in_time.tv_nsec;
+	if (diff.tv_nsec < 0) {
+		diff.tv_sec--;
+		diff.tv_nsec += 1000000000L;
+	}
+	snprintf(buf,50,"%lld%.9ld", (long long)diff.tv_sec, diff.tv_nsec);
+}
+
+struct FrameMetadata {
+	KrkCodeObject * target_obj; /* Function being entered */
+	size_t target_line;         /* First line seen in the entered function */
+	size_t count;               /* Instruction count on entry */
+	size_t source_line;         /* Line we came from in the caller */
+	KrkCodeObject * source_obj; /* Function we came from in the caller */
+	struct timespec in_time;    /* Time of frame entry */
+};
+
+static struct FrameMetadata frameMetadata[KRK_CALL_FRAMES_MAX];
+
+int krk_callgrind_debuggerHook(KrkCallFrame * frame) {
+	instrCounter++;
+
+	if (krk_currentThread.frameCount != lastFrameCount) {
+		if (krk_currentThread.frameCount > lastFrameCount) {
+			/* When we detect function entry, record details of the function being called
+			 * and what called in, and record the current time. */
+			KrkCallFrame * prev = lastFrameCount ? &krk_currentThread.frames[lastFrameCount-1] : NULL;
+			frameMetadata[lastFrameCount].target_obj = frame->closure->function;
+			frameMetadata[lastFrameCount].target_line = krk_lineNumber(&frame->closure->function->chunk, frame->ip - frame->closure->function->chunk.code);
+			frameMetadata[lastFrameCount].count = instrCounter;
+			frameMetadata[lastFrameCount].source_obj = prev ? prev->closure->function : NULL;
+			frameMetadata[lastFrameCount].source_line = prev ? krk_lineNumber(&prev->closure->function->chunk, prev->ip - 1 - prev->closure->function->chunk.code) : 0;
+			clock_gettime(CLOCK_MONOTONIC, &frameMetadata[lastFrameCount].in_time);
+			functionsEntered++;
+		} else {
+			size_t procFrame = lastFrameCount - 1;
+			while (procFrame >= krk_currentThread.frameCount) {
+				if (procFrame == 0) {
+					/* This is the outermost call, eg. <module>, returning to the interpreter. We still want to make
+					 * sure we collect the time spent in the call and add it to the time for the function, so that
+					 * the time spent inside other function calls is subtracted to get the time spent actually
+					 * executing code in the module. */
+					char tmp[50];
+					time_diff(frameMetadata[procFrame].in_time, tmp);
+					KrkValue diffTime = krk_parse_int(tmp,strlen(tmp),10);
+					krk_push(diffTime);
+					KrkValue totalTime = INTEGER_VAL(0);
+					krk_tableGet(AS_DICT(timeCache),OBJECT_VAL(frameMetadata[procFrame].target_obj),&totalTime);
+					krk_push(krk_operator_add(totalTime,diffTime));
+					krk_tableSet(AS_DICT(timeCache),OBJECT_VAL(frameMetadata[procFrame].target_obj),krk_peek(0));
+					krk_pop();
+					krk_pop();
+					break;
+				}
+
+				/* Set up dict for call mappings */
+				KrkValue ndict = NONE_VAL();
+				if (!krk_tableGet(AS_DICT(callCache),OBJECT_VAL(frameMetadata[procFrame].source_obj),&ndict)) {
+					ndict = krk_dict_of(0,NULL,0);
+					krk_push(ndict);
+					krk_tableSet(AS_DICT(callCache),OBJECT_VAL(frameMetadata[procFrame].source_obj),ndict);
+					krk_pop();
+				}
+
+				KrkTuple * t = krk_newTuple(3);
+				krk_push(OBJECT_VAL(t));
+
+				/* Target code object */
+				t->values.values[t->values.count++] = OBJECT_VAL(frameMetadata[procFrame].target_obj);
+
+				/* Target and source lines */
+				t->values.values[t->values.count++] = INTEGER_VAL(frameMetadata[procFrame].target_line);
+				t->values.values[t->values.count++] = INTEGER_VAL(frameMetadata[procFrame].source_line);
+
+				KrkValue nlist = NONE_VAL();
+				if (!krk_tableGet(AS_DICT(ndict),krk_peek(0),&nlist)) {
+					nlist = krk_list_of(3,(const KrkValue[]){INTEGER_VAL(0),INTEGER_VAL(0),INTEGER_VAL(0)},0);
+					krk_push(nlist);
+					krk_tableSet(AS_DICT(ndict),krk_peek(1),krk_peek(0));
+					krk_pop();
+				}
+				krk_pop(); /* tuple */
+
+				/* totalCalls += 1 */
+				krk_push(krk_operator_add(AS_LIST(nlist)->values[0],INTEGER_VAL(1)));
+				AS_LIST(nlist)->values[0] = krk_pop();
+
+				/* totalCosts += last cost */
+				char tmp[50];
+				snprintf(tmp,50,"%zu", instrCounter - frameMetadata[procFrame].count);
+				KrkValue diffCount = krk_parse_int(tmp,strlen(tmp),10);
+				krk_push(diffCount);
+				krk_push(krk_operator_add(AS_LIST(nlist)->values[1],diffCount));
+				AS_LIST(nlist)->values[1] = krk_pop();
+				krk_pop(); /* diffCount */
+
+				time_diff(frameMetadata[procFrame].in_time, tmp); /* Time for this call */
+				KrkValue diffTime = krk_parse_int(tmp,strlen(tmp),10);
+				krk_push(diffTime);
+				krk_push(krk_operator_add(AS_LIST(nlist)->values[2],diffTime));
+				AS_LIST(nlist)->values[2] = krk_pop();
+
+				KrkValue myTime = INTEGER_VAL(0); /* Time spent here */
+				krk_tableGet(AS_DICT(timeCache),OBJECT_VAL(frameMetadata[procFrame].target_obj),&myTime);
+				krk_push(krk_operator_add(myTime,diffTime));
+				krk_tableSet(AS_DICT(timeCache),OBJECT_VAL(frameMetadata[procFrame].target_obj),krk_peek(0));
+				krk_pop(); /* myTime + diffTime */
+
+				KrkValue parentTime = INTEGER_VAL(0); /* Was not spent there */
+				krk_tableGet(AS_DICT(timeCache),OBJECT_VAL(frameMetadata[procFrame].source_obj),&parentTime);
+				krk_push(krk_operator_sub(parentTime,diffTime));
+				krk_tableSet(AS_DICT(timeCache),OBJECT_VAL(frameMetadata[procFrame].source_obj),krk_peek(0));
+				krk_pop(); /* parentTime - diffTime */
+
+				krk_pop(); /* diffTime */
+
+				memset(&frameMetadata[procFrame], 0, sizeof(struct FrameMetadata));
+				procFrame--;
+			}
+		}
+		lastFrameCount = krk_currentThread.frameCount;
+	}
+
+	if (!frame) return KRK_DEBUGGER_QUIT;
+
+	/* Set up dict for instruction counts */
+	KrkValue ndict = NONE_VAL();
+	if (!krk_tableGet(AS_DICT(lineCache),OBJECT_VAL(frame->closure->function),&ndict)) {
+		ndict = krk_dict_of(0,NULL,0);
+		krk_push(ndict);
+		krk_tableSet(AS_DICT(lineCache),OBJECT_VAL(frame->closure->function),ndict);
+		krk_pop();
+	}
+
+	KrkValue lineNumber = INTEGER_VAL(krk_lineNumber(&frame->closure->function->chunk, frame->ip - frame->closure->function->chunk.code));
+
+	/* Add one to instruction count for this line */
+	KrkValue count = INTEGER_VAL(0);
+	krk_tableGet(AS_DICT(ndict), lineNumber, &count);
+	krk_push(krk_operator_add(count, INTEGER_VAL(1)));
+	krk_tableSet(AS_DICT(ndict), lineNumber, krk_peek(0));
+	krk_pop(); /* count + 1 */
+
+	return KRK_DEBUGGER_STEP;
+}
+
+
+int main(int argc, char *argv[]) {
+	char outfile[1024];
+	snprintf(outfile,1024,"callgrind.out.%d",getpid());
+
+	int opt;
+	while ((opt = getopt(argc, argv, "+:f:-:")) != -1) {
+		switch (opt) {
+			case 'f':
+				snprintf(outfile,1024,"%s", optarg);
+				break;
+			case '?':
+				if (optopt != '-') {
+					fprintf(stderr, "%s: unrocognized option '%c'\n", argv[0], optopt);
+					return 1;
+				}
+				optarg = argv[optind]+1;
+				/* fall through */
+			case '-':
+				if (!strcmp(optarg,"help")) {
+				} else {
+					fprintf(stderr, "%s: unrecognized option: '--%s'\n", argv[0], optarg);
+					return 1;
+				}
+		}
+	}
+	if (optind == argc) {
+		return usage(argv);
+	}
+
+	findInterpreter(argv);
+	krk_initVM(KRK_THREAD_SINGLE_STEP);
+	krk_debug_registerCallback(krk_callgrind_debuggerHook);
+	addArgs(argc,argv);
+
+	krk_startModule("__main__");
+
+	lineCache = krk_dict_of(0,NULL,0);
+	krk_attachNamedValue(&krk_currentThread.module->fields,"__line_cache__",lineCache);
+	callCache = krk_dict_of(0,NULL,0);
+	krk_attachNamedValue(&krk_currentThread.module->fields,"__call_cache__",callCache);
+	timeCache = krk_dict_of(0,NULL,0);
+	krk_attachNamedValue(&krk_currentThread.module->fields,"__time_cache__",timeCache);
+
+	krk_runfile(argv[optind],argv[optind]);
+
+	if (krk_currentThread.flags & KRK_THREAD_HAS_EXCEPTION) {
+		krk_currentThread.flags &= ~(KRK_THREAD_HAS_EXCEPTION);
+		fprintf(stderr, "== Executed ended by exception ==\n");
+	} else {
+		fprintf(stderr, "== Execution completed ==\n");
+	}
+	krk_callgrind_debuggerHook(NULL);
+
+	fprintf(stderr, "%10zu total instruction%s\n", instrCounter, (instrCounter != 1) ? "s" : "");
+	fprintf(stderr, "%10zu function%s calls\n", functionsEntered, (functionsEntered != 1) ? "s" : "");
+
+	FILE * f = fopen(outfile,"w");
+	if (!f) {
+		fprintf(stderr, "%s: %s: %s\n", argv[0], outfile, strerror(errno));
+		return 1;
+	}
+
+	fprintf(f,"# callgrind format\n");
+	fprintf(f,"creator: Kuroko\n");
+	fprintf(f,"positions: line\n");
+	fprintf(f,"events: instructions nanoseconds\n");
+	fprintf(f,"cmd: %s %s\n", argv[0], argv[optind]);
+	fprintf(f,"summary: %zu ", instrCounter);
+	char tmp[50];
+	time_diff(frameMetadata[0].in_time, tmp);
+	fprintf(f,"%s\n", tmp);
+
+
+	for (size_t j = 0; j < AS_DICT(lineCache)->used; ++j) {
+		if (IS_KWARGS(AS_DICT(lineCache)->entries[j].key)) continue;
+
+		KrkCodeObject * function = (void*)AS_OBJECT(AS_DICT(lineCache)->entries[j].key);
+		KrkValue        ndict    = AS_DICT(lineCache)->entries[j].value;
+
+		fprintf(f,"fl=%s\n", function->chunk.filename->chars);
+		fprintf(f,"fn=%s@%p\n", function->qualname ? function->qualname->chars : function->name->chars, (void*)function);
+
+		KrkValue timeValue = NONE_VAL();
+		krk_tableGet(AS_DICT(timeCache), OBJECT_VAL(function), &timeValue);
+		if (!IS_NONE(timeValue)) {
+			fprintf(f,"%zu ", (size_t)krk_lineNumber(&function->chunk, 0));
+			struct StringBuilder sb = {0};
+			krk_pushStringBuilderFormat(&sb, "0 %R\n", timeValue);
+			fprintf(f,"%.*s", (int)sb.length, sb.bytes);
+			krk_discardStringBuilder(&sb);
+		}
+
+		for (size_t k = 0; k < AS_DICT(ndict)->used; ++k) {
+			if (IS_KWARGS(AS_DICT(ndict)->entries[k].key)) continue;
+			struct StringBuilder sb = {0};
+			krk_pushStringBuilderFormat(&sb, "%R %R 0\n", AS_DICT(ndict)->entries[k].key, AS_DICT(ndict)->entries[k].value);
+			fprintf(f,"%.*s", (int)sb.length, sb.bytes);
+			krk_discardStringBuilder(&sb);
+		}
+
+		KrkValue cdict = NONE_VAL();
+		krk_tableGet(AS_DICT(callCache), OBJECT_VAL(function), &cdict);
+		if (!IS_NONE(cdict)) {
+			for (size_t l = 0; l < AS_DICT(cdict)->used; ++l) {
+				if (IS_KWARGS(AS_DICT(cdict)->entries[l].key)) continue;
+
+				KrkCodeObject * target = (void*)AS_OBJECT(AS_TUPLE(AS_DICT(cdict)->entries[l].key)->values.values[0]);
+				KrkValue targetLine    = AS_TUPLE(AS_DICT(cdict)->entries[l].key)->values.values[1];
+				KrkValue sourceLine    = AS_TUPLE(AS_DICT(cdict)->entries[l].key)->values.values[2];
+				KrkValue totalCalls    = AS_LIST(AS_DICT(cdict)->entries[l].value)->values[0];
+				KrkValue totalCost     = AS_LIST(AS_DICT(cdict)->entries[l].value)->values[1];
+				KrkValue totalTime     = AS_LIST(AS_DICT(cdict)->entries[l].value)->values[2];
+
+				fprintf(f,"cfi=%s\n", target->chunk.filename->chars);
+				fprintf(f,"cfn=%s@%p\n", target->qualname ? target->qualname->chars : target->name->chars, (void*)target);
+
+				struct StringBuilder sb = {0};
+				krk_pushStringBuilderFormat(&sb, "calls=%R %R\n%R %R %R\n", totalCalls, targetLine, sourceLine, totalCost, totalTime);
+				fprintf(f,"%.*s",(int)sb.length,sb.bytes);
+				krk_discardStringBuilder(&sb);
+			}
+		}
+	}
+
+	fclose(f);
+
+	krk_freeVM();
+	return 0;
+}
+
diff --git a/tools/common.h b/tools/common.h
new file mode 100644
index 0000000..1ddfb46
--- /dev/null
+++ b/tools/common.h
@@ -0,0 +1,57 @@
+#include <stdlib.h>
+#include <kuroko/kuroko.h>
+#include <kuroko/vm.h>
+
+/* Copied from src/kuroko.c */
+static void findInterpreter(char * argv[]) {
+#ifdef _WIN32
+	vm.binpath = strdup(_pgmptr);
+#else
+	/* Try asking /proc */
+	char tmp[4096];
+	char * binpath = realpath("/proc/self/exe", NULL);
+	if (!binpath || (access(binpath, X_OK) != 0)) {
+		if (binpath) {
+			free(binpath);
+			binpath = NULL;
+		}
+		if (strchr(argv[0], '/')) {
+			binpath = realpath(argv[0], NULL);
+		} else {
+			/* Search PATH for argv[0] */
+			char * p = getenv("PATH");
+			if (!p) return;
+			char * _path = strdup(p);
+			char * path = _path;
+			while (path) {
+				char * next = strchr(path,':');
+				if (next) *next++ = '\0';
+
+				snprintf(tmp, 4096, "%s/%s", path, argv[0]);
+				if (access(tmp, X_OK) == 0) {
+					binpath = strdup(tmp);
+					break;
+				}
+				path = next;
+			}
+			free(_path);
+		}
+	}
+	if (binpath) {
+		vm.binpath = binpath;
+	} /* Else, give up at this point and just don't attach it at all. */
+#endif
+}
+
+/* Collect arguments for script, also copied from src/kuroko.c */
+static void addArgs(int argc, char * argv[]) {
+	for (int arg = optind; arg < argc; ++arg) {
+		krk_push(OBJECT_VAL(krk_copyString(argv[arg],strlen(argv[arg]))));
+	}
+	KrkValue argList = krk_callNativeOnStack(argc - optind + (optind == argc), &krk_currentThread.stackTop[-(argc - optind + (optind == argc))], 0, krk_list_of);
+	krk_push(argList);
+	krk_attachNamedValue(&vm.system->fields, "argv", argList);
+	krk_pop();
+	for (int arg = optind; arg < argc + (optind == argc); ++arg) krk_pop();
+}
+
diff --git a/tools/watchdog.c b/tools/watchdog.c
new file mode 100644
index 0000000..a29c15c
--- /dev/null
+++ b/tools/watchdog.c
@@ -0,0 +1,71 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <time.h>
+#include <errno.h>
+#include <kuroko/kuroko.h>
+#include <kuroko/vm.h>
+#include <kuroko/debug.h>
+#include <kuroko/util.h>
+
+#include "common.h"
+
+static int usage(char * argv[]) {
+	fprintf(stderr, "usage: %s [-s count] [FILE] [args...]\n", argv[0]);
+	return 1;
+}
+
+static size_t instrCounter = 0;     /* Total counter of executed instructions */
+static size_t stopAt = 500000;
+
+int krk_callgrind_debuggerHook(KrkCallFrame * frame) {
+	instrCounter++;
+	if (instrCounter < stopAt) return KRK_DEBUGGER_STEP;
+	if (instrCounter == stopAt) {
+		krk_runtimeError(vm.exceptions->baseException, "Watchdog counter expired.");
+	}
+	return KRK_DEBUGGER_CONTINUE;
+}
+
+
+int main(int argc, char *argv[]) {
+	int opt;
+	while ((opt = getopt(argc, argv, "+:s:-:")) != -1) {
+		switch (opt) {
+			case 's':
+				stopAt = strtoul(optarg,NULL,10);
+				break;
+			case '?':
+				if (optopt != '-') {
+					fprintf(stderr, "%s: unrocognized option '%c'\n", argv[0], optopt);
+					return 1;
+				}
+				optarg = argv[optind]+1;
+				/* fall through */
+			case '-':
+				if (!strcmp(optarg,"help")) {
+				} else {
+					fprintf(stderr, "%s: unrecognized option: '--%s'\n", argv[0], optarg);
+					return 1;
+				}
+		}
+	}
+
+	if (optind == argc) {
+		return usage(argv);
+	}
+
+	findInterpreter(argv);
+	krk_initVM(KRK_THREAD_SINGLE_STEP);
+	krk_debug_registerCallback(krk_callgrind_debuggerHook);
+	addArgs(argc,argv);
+
+	krk_startModule("__main__");
+	krk_runfile(argv[optind],argv[optind]);
+
+	fprintf(stderr, "%zu total instructions\n", instrCounter);
+
+	krk_freeVM();
+	return 0;
+}
+
+