diff --git a/doc/OpenSTA.odt b/doc/OpenSTA.odt
index c445ecd0..bf8029c0 100644
Binary files a/doc/OpenSTA.odt and b/doc/OpenSTA.odt differ
diff --git a/doc/OpenSTA.pdf b/doc/OpenSTA.pdf
index f69ea92a..ed8ec03e 100644
Binary files a/doc/OpenSTA.pdf and b/doc/OpenSTA.pdf differ
diff --git a/include/sta/PathExpanded.hh b/include/sta/PathExpanded.hh
index f62b302a..d943e7c9 100644
--- a/include/sta/PathExpanded.hh
+++ b/include/sta/PathExpanded.hh
@@ -40,7 +40,7 @@ public:
   size_t size() const { return paths_.size(); }
   // path(0) is the startpoint.
   // path(size()-1) is the endpoint.
-  PathRef *path(size_t index);
+  const PathRef *path(size_t index) const;
   TimingArc *prevArc(size_t index);
   // Returns the path start point.
   //  Register/Latch Q pin
diff --git a/include/sta/Sta.hh b/include/sta/Sta.hh
index 52c2ef2d..fa735883 100644
--- a/include/sta/Sta.hh
+++ b/include/sta/Sta.hh
@@ -905,9 +905,9 @@ public:
   //   Previous path end is used to detect path group changes
   //   so headers are reported by group.
   void reportPathEnd(PathEnd *end,
-		     PathEnd *prev_end);
+		     PathEnd *prev_end,
+                     bool last);
   void reportPathEnd(PathEnd *end);
-  void reportPathEnds(PathEndSeq *ends);
   ReportPath *reportPath() { return report_path_; }
   void reportPath(Path *path);
 
diff --git a/include/sta/StringUtil.hh b/include/sta/StringUtil.hh
index c2a117a5..3b2f6cee 100644
--- a/include/sta/StringUtil.hh
+++ b/include/sta/StringUtil.hh
@@ -169,6 +169,11 @@ void
 stringPrint(string &str,
 	    const char *fmt,
 	    ...) __attribute__((format (printf, 2, 3)));
+// Formated append to std::string.
+void
+stringAppend(string &str,
+             const char *fmt,
+             ...) __attribute__((format (printf, 2, 3)));
 
 // Print to a temporary string.
 char *
diff --git a/search/PathExpanded.cc b/search/PathExpanded.cc
index 972e3bfa..8c63e5b2 100644
--- a/search/PathExpanded.cc
+++ b/search/PathExpanded.cc
@@ -146,8 +146,8 @@ PathExpanded::startIndex() const
   return pathsIndex(start_index_);
 }
 
-PathRef *
-PathExpanded::path(size_t index)
+const PathRef *
+PathExpanded::path(size_t index) const
 {
   if (index < paths_.size())
     return &paths_[pathsIndex(index)];
diff --git a/search/Property.cc b/search/Property.cc
index 01491905..568ec68c 100644
--- a/search/Property.cc
+++ b/search/Property.cc
@@ -1260,7 +1260,7 @@ getProperty(PathEnd *end,
     PathExpanded expanded(end->path(), sta);
     PathRefSeq paths;
     for (auto i = expanded.startIndex(); i < expanded.size(); i++) {
-      PathRef *path = expanded.path(i);
+      const PathRef *path = expanded.path(i);
       paths.push_back(*path);
     }
     return PropertyValue(&paths);
diff --git a/search/ReportPath.cc b/search/ReportPath.cc
index f19f2e9e..3770bd05 100644
--- a/search/ReportPath.cc
+++ b/search/ReportPath.cc
@@ -269,58 +269,16 @@ ReportPath::setReportSigmas(bool report)
 
 ////////////////////////////////////////////////////////////////
 
-void
-ReportPath::reportPathEndHeader()
-{
-  switch (format_) {
-  case ReportPathFormat::full:
-  case ReportPathFormat::full_clock:
-  case ReportPathFormat::full_clock_expanded:
-  case ReportPathFormat::shorter:
-  case ReportPathFormat::endpoint:
-    break;
-  case ReportPathFormat::summary:
-    reportSummaryHeader();
-    break;
-  case ReportPathFormat::slack_only:
-    reportSlackOnlyHeader();
-    break;
-  default:
-    report_->critical(1470, "unsupported path type");
-    break;
-  }
-}
-
-void
-ReportPath::reportPathEndFooter()
-{
-  string header;
-  switch (format_) {
-  case ReportPathFormat::full:
-  case ReportPathFormat::full_clock:
-  case ReportPathFormat::full_clock_expanded:
-  case ReportPathFormat::shorter:
-    break;
-  case ReportPathFormat::endpoint:
-  case ReportPathFormat::summary:
-  case ReportPathFormat::slack_only:
-    reportBlankLine();
-    break;
-  default:
-    report_->critical(1471, "unsupported path type");
-    break;
-  }
-}
-
 void
 ReportPath::reportPathEnd(PathEnd *end)
 {
-  reportPathEnd(end, nullptr);
+  reportPathEnd(end, nullptr, true);
 }
 
 void
 ReportPath::reportPathEnd(PathEnd *end,
-			  PathEnd *prev_end)
+			  PathEnd *prev_end,
+                          bool last)
 {
   switch (format_) {
   case ReportPathFormat::full:
@@ -345,8 +303,8 @@ ReportPath::reportPathEnd(PathEnd *end,
   case ReportPathFormat::slack_only:
     reportSlackOnly(end);
     break;
-  default:
-    report_->critical(1473, "unsupported path type");
+  case ReportPathFormat::json:
+    reportJson(end, last);
     break;
   }
 }
@@ -367,6 +325,49 @@ ReportPath::reportPathEnds(PathEndSeq *ends)
   reportPathEndFooter();
 }
 
+void
+ReportPath::reportPathEndHeader()
+{
+  switch (format_) {
+  case ReportPathFormat::full:
+  case ReportPathFormat::full_clock:
+  case ReportPathFormat::full_clock_expanded:
+  case ReportPathFormat::shorter:
+  case ReportPathFormat::endpoint:
+    break;
+  case ReportPathFormat::summary:
+    reportSummaryHeader();
+    break;
+  case ReportPathFormat::slack_only:
+    reportSlackOnlyHeader();
+    break;
+  case ReportPathFormat::json:
+    reportJsonHeader();
+    break;
+  }
+}
+
+void
+ReportPath::reportPathEndFooter()
+{
+  string header;
+  switch (format_) {
+  case ReportPathFormat::full:
+  case ReportPathFormat::full_clock:
+  case ReportPathFormat::full_clock_expanded:
+  case ReportPathFormat::shorter:
+    break;
+  case ReportPathFormat::endpoint:
+  case ReportPathFormat::summary:
+  case ReportPathFormat::slack_only:
+    reportBlankLine();
+    break;
+  case ReportPathFormat::json:
+    reportJsonFooter();
+    break;
+  }
+}
+
 void
 ReportPath::reportEndpointHeader(PathEnd *end,
 				 PathEnd *prev_end)
@@ -1043,6 +1044,146 @@ ReportPath::pathEndpoint(PathEnd *end)
 
 ////////////////////////////////////////////////////////////////
 
+void
+ReportPath::reportJsonHeader()
+{
+  report_->reportLine("{\"checks\": [");
+}
+
+void
+ReportPath::reportJsonFooter()
+{
+  report_->reportLine("]");
+  report_->reportLine("}");
+}
+
+void
+ReportPath::reportJson(const PathEnd *end,
+                       bool last)
+{
+  string result;
+  result += "{\n";
+  stringAppend(result, "  \"type\": \"%s\",\n", end->typeName());
+  stringAppend(result, "  \"path_group\": \"%s\",\n",
+               search_->pathGroup(end)->name());
+  stringAppend(result, "  \"path_type\": \"%s\",\n",
+               end->minMax(this)->asString());
+
+  PathExpanded expanded(end->path(), this);
+  const Pin *startpoint = expanded.startPath()->vertex(this)->pin();
+  const Pin *endpoint = expanded.endPath()->vertex(this)->pin();
+  stringAppend(result, "  \"startpoint\": \"%s\",\n",
+               network_->pathName(startpoint));
+  stringAppend(result, "  \"endpoint\": \"%s\",\n",
+               network_->pathName(endpoint));
+
+  const ClockEdge *src_clk_edge = end->sourceClkEdge(this);
+  const PathVertex *tgt_clk_path = end->targetClkPath();
+  if (src_clk_edge) {
+    stringAppend(result, "  \"source_clock\": \"%s\",\n",
+                 src_clk_edge->clock()->name());
+    stringAppend(result, "  \"source_clock_edge\": \"%s\",\n",
+                 src_clk_edge->transition()->name());
+  }
+  reportJson(expanded, "source_path", 2, !end->isUnconstrained(), result);
+
+  const ClockEdge *tgt_clk_edge = end->targetClkEdge(this);
+  if (tgt_clk_edge) {
+    stringAppend(result, "  \"target_clock\": \"%s\",\n",
+                 tgt_clk_edge->clock()->name());
+    stringAppend(result, "  \"target_clock_edge\": \"%s\",\n",
+                 tgt_clk_edge->transition()->name());
+  }
+  if (tgt_clk_path)
+    reportJson(end->targetClkPath(), "target_clock_path", 2, true, result);
+
+  if (end->checkRole(this)) {
+    stringAppend(result, "  \"data_arrival_time\": %.3e,\n",
+                 end->dataArrivalTimeOffset(this));
+
+    const MultiCyclePath *mcp = end->multiCyclePath();
+    if (mcp)
+      stringAppend(result, "  \"multi_cycle_path\": %d,\n",
+                   mcp->pathMultiplier());
+
+    PathDelay *path_delay = end->pathDelay();
+    if (path_delay)
+      stringAppend(result, "  \"path_delay\": %.3e,\n",
+                   path_delay->delay());
+
+    stringAppend(result, "  \"crpr\": %.3e,\n", end->checkCrpr(this));
+    stringAppend(result, "  \"margin\": %.3e,\n", end->margin(this));
+    stringAppend(result, "  \"required_time\": %.3e,\n",
+                 end->requiredTimeOffset(this));
+    stringAppend(result, "  \"slack\": %.3e\n", end->slack(this));
+  }
+  result += "}";
+  if (!last)
+    result += ",";
+  report_->reportLineString(result);
+}
+
+void
+ReportPath::reportJson(const Path *path)
+{
+  string result;
+  result += "{\n";
+  reportJson(path, "path", 0, false, result);
+  result += "}\n";
+  report_->reportLineString(result);
+}
+
+void
+ReportPath::reportJson(const Path *path,
+                       const char *path_name,
+                       int indent,
+                       bool trailing_comma,
+                       string &result)
+{
+  PathExpanded expanded(path, this);
+  reportJson(expanded, path_name, indent, trailing_comma, result);
+}
+
+void
+ReportPath::reportJson(const PathExpanded &expanded,
+                       const char *path_name,
+                       int indent,
+                       bool trailing_comma,
+                       string &result)
+{
+  stringAppend(result, "%*s\"%s\": [\n", indent, "", path_name);
+  for (size_t i = 0; i < expanded.size(); i++) {
+    const PathRef *path = expanded.path(i);
+    const Pin *pin = path->vertex(this)->pin();
+    stringAppend(result, "%*s  {\n", indent, "");
+    stringAppend(result, "%*s    \"pin\": \"%s\",\n",
+                 indent, "",
+                 network_->pathName(pin));
+    double x, y;
+    bool exists;
+    network_->location(pin, x, y, exists);
+    if (exists) {
+      stringAppend(result, "%*s    \"x\": %.9f,\n", indent, "", x);
+      stringAppend(result, "%*s    \"y\": %.9f,\n", indent, "", y);
+    }
+
+    stringAppend(result, "%*s    \"arrival\": %.3e,\n",
+                 indent, "",
+                 delayAsFloat(path->arrival(this)));
+    stringAppend(result, "%*s    \"slew\": %.3e\n",
+                 indent, "",
+                 delayAsFloat(path->slew(this)));
+    stringAppend(result, "%*s  }%s\n",
+                 indent, "",
+                 (i < expanded.size() - 1) ? "," : "");
+  }
+  stringAppend(result, "%*s]%s\n",
+               indent, "",
+               trailing_comma ? "," : "");
+}
+
+////////////////////////////////////////////////////////////////
+
 void
 ReportPath::reportSlackOnlyHeader()
 {
@@ -2365,12 +2506,13 @@ ReportPath::reportPath(const Path *path)
     reportPathFull(path);
     break;
   case ReportPathFormat::json:
-    reportPathJson(path);
+    reportJson(path);
     break;
+  case ReportPathFormat::shorter:
+  case ReportPathFormat::endpoint:
   case ReportPathFormat::summary:
   case ReportPathFormat::slack_only:
-  default:
-    report_->critical(1474, "unsupported path type");
+    report_->reportLine("Format not supported.");
     break;
   }
 }
@@ -2383,54 +2525,7 @@ ReportPath::reportPathFull(const Path *path)
   reportSrcClkAndPath(path, expanded, 0.0, delay_zero, delay_zero, false);
 }
 
-void
-ReportPath::reportPathJson(const Path *path)
-{
-  report_->reportLine("{ \"path\": [");
-  PathExpanded expanded(path, this);
-  for (auto i = expanded.startIndex(); i < expanded.size(); i++) {
-    string line;
-    PathRef *path = expanded.path(i);
-    const Pin *pin = path->vertex(this)->pin();
-    report_->reportLine("    {");
-    line = "       \"pin\": \"";
-    line += network_->pathName(pin);
-    line += "\",";
-    report_->reportLineString(line);
-
-    double x, y;
-    bool exists;
-    string tmp;
-    network_->location(pin, x, y, exists);
-    if (exists) {
-      line = "       \"x\": ";
-      stringPrint(tmp, "%.9f", x);
-      line += tmp + ",\n";
-      line += "       \"y\": ";
-      stringPrint(tmp, "%.9f", y);
-      line += tmp + ",";
-      report_->reportLineString(line);
-    }
-
-    line = "       \"arrival\": ";
-    stringPrint(tmp, "%.3e", delayAsFloat(path->arrival(this)));
-    line += tmp;
-    line += ",";
-    report_->reportLineString(line);
-
-    line = "       \"slew\": ";
-    stringPrint(tmp, "%.3e", delayAsFloat(path->slew(this)));
-    line += tmp;
-    report_->reportLineString(line);
-
-    line = "    }";
-    if (i < expanded.size() - 1)
-      line += ",";
-    report_->reportLineString(line);
-  }
-  report_->reportLine("  ]");
-  report_->reportLine("}");
-}
+////////////////////////////////////////////////////////////////
 
 void
 ReportPath::reportPath1(const Path *path,
@@ -2517,7 +2612,7 @@ ReportPath::reportPath4(const Path *path,
   Arrival prev_time(0.0);
   if (skip_first_path) {
     path_first_index = 1;
-    PathRef *start = expanded.path(0);
+    const PathRef *start = expanded.path(0);
     prev_time = start->arrival(this) + time_offset;
   }
   size_t path_last_index = expanded.size() - 1;
@@ -2551,7 +2646,7 @@ ReportPath::reportPath5(const Path *path,
   expanded.clkPath(clk_path);
   Vertex *clk_start = clk_path.vertex(this);
   for (size_t i = path_first_index; i <= path_last_index; i++) {
-    PathRef *path1 = expanded.path(i);
+    const PathRef *path1 = expanded.path(i);
     TimingArc *prev_arc = expanded.prevArc(i);
     Vertex *vertex = path1->vertex(this);
     Pin *pin = vertex->pin();
diff --git a/search/ReportPath.hh b/search/ReportPath.hh
index 75778cc0..f2017a14 100644
--- a/search/ReportPath.hh
+++ b/search/ReportPath.hh
@@ -61,7 +61,8 @@ public:
   //   Previous path end is used to detect path group changes
   //   so headers are reported by group.
   void reportPathEnd(PathEnd *end,
-		     PathEnd *prev_end);
+		     PathEnd *prev_end,
+                     bool last);
   void reportPathEnds(PathEndSeq *ends);
   void reportPath(const Path *path);
 
@@ -81,6 +82,22 @@ public:
   void reportFull(const PathEndGatedClock *end);
   void reportFull(const PathEndDataCheck *end);
 
+  void reportJsonHeader();
+  void reportJsonFooter();
+  void reportJson(const PathEnd *end,
+                  bool last);
+  void reportJson(const Path *path);
+  void reportJson(const Path *path,
+                  const char *path_name,
+                  int indent,
+                  bool trailing_comma,
+                  string &result);
+  void reportJson(const PathExpanded &expanded,
+                  const char *path_name,
+                  int indent,
+                  bool trailing_comma,
+                  string &result);
+
   void reportEndHeader();
   void reportEndLine(PathEnd *end);
 
@@ -264,7 +281,6 @@ protected:
   void reportPath(const PathEnd *end,
 		  PathExpanded &expanded);
   void reportPathFull(const Path *path);
-  void reportPathJson(const Path *path);
   void reportPathHeader();
   void reportPath1(const Path *path,
 		   PathExpanded &expanded,
diff --git a/search/Search.i b/search/Search.i
index da07b521..e90f03a8 100644
--- a/search/Search.i
+++ b/search/Search.i
@@ -480,9 +480,10 @@ report_path_end(PathEnd *end)
 
 void
 report_path_end2(PathEnd *end,
-		 PathEnd *prev_end)
+		 PathEnd *prev_end,
+                 bool last)
 {
-  Sta::sta()->reportPathEnd(end, prev_end);
+  Sta::sta()->reportPathEnd(end, prev_end, last);
 }
 
 void
diff --git a/search/Search.tcl b/search/Search.tcl
index f6e5af90..76689129 100644
--- a/search/Search.tcl
+++ b/search/Search.tcl
@@ -1069,9 +1069,12 @@ proc parse_path_group_arg { group_names } {
 proc report_path_ends { path_ends } {
   report_path_end_header
   set prev_end "NULL"
+  set end_count [llength $path_ends]
+  set i 0
   foreach path_end $path_ends {
-    report_path_end2 $path_end $prev_end
+    report_path_end2 $path_end $prev_end [expr $i == ($end_count - 1)]
     set prev_end $path_end
+    incr i
   }
   report_path_end_footer
 }
diff --git a/search/Sta.cc b/search/Sta.cc
index 1416edd6..175d1215 100644
--- a/search/Sta.cc
+++ b/search/Sta.cc
@@ -2518,12 +2518,6 @@ Sta::setReportPathSigmas(bool report_sigmas)
   report_path_->setReportSigmas(report_sigmas);
 }
 
-void
-Sta::reportPathEnds(PathEndSeq *ends)
-{
-  report_path_->reportPathEnds(ends);
-}
-
 void
 Sta::reportPathEndHeader()
 {
@@ -2544,9 +2538,10 @@ Sta::reportPathEnd(PathEnd *end)
 
 void
 Sta::reportPathEnd(PathEnd *end,
-		   PathEnd *prev_end)
+		   PathEnd *prev_end,
+                   bool last)
 {
-  report_path_->reportPathEnd(end, prev_end);
+  report_path_->reportPathEnd(end, prev_end, last);
 }
 
 void
diff --git a/spice/WritePathSpice.cc b/spice/WritePathSpice.cc
index ab6509fe..50607b5b 100644
--- a/spice/WritePathSpice.cc
+++ b/spice/WritePathSpice.cc
@@ -84,10 +84,10 @@ private:
   float maxTime();
   float pathMaxTime();
   void writeMeasureDelayStmt(Stage stage,
-			     Path *from_path,
-			     Path *to_path);
+			     const Path *from_path,
+			     const Path *to_path);
   void writeMeasureSlewStmt(Stage stage,
-			    Path *path);
+			    const Path *path);
   void writeInputWaveform();
   void writeClkWaveform();
 
@@ -110,9 +110,9 @@ private:
   int stageGateInputPathIndex(Stage stage);
   int stageDrvrPathIndex(Stage stage);
   int stageLoadPathIndex(Stage stage);
-  PathRef *stageGateInputPath(Stage stage);
-  PathRef *stageDrvrPath(Stage stage);
-  PathRef *stageLoadPath(Stage stage);
+  const PathRef *stageGateInputPath(Stage stage);
+  const PathRef *stageDrvrPath(Stage stage);
+  const PathRef *stageLoadPath(Stage stage);
   TimingArc *stageGateArc(Stage stage);
   TimingArc *stageWireArc(Stage stage);
   Edge *stageGateEdge(Stage stage);
@@ -128,8 +128,8 @@ private:
   LibertyCell *stageLibertyCell(Stage stage);
   Instance *stageInstance(Stage stage);
 
-  float findSlew(Path *path);
-  float findSlew(Path *path,
+  float findSlew(const Path *path);
+  float findSlew(const Path *path,
 		 const RiseFall *rf,
 		 TimingArc *next_arc);
   Path *path_;
@@ -240,7 +240,7 @@ float
 WritePathSpice::maxTime()
 {
   Stage input_stage = stageFirst();
-  PathRef *input_path = stageDrvrPath(input_stage);
+  const PathRef *input_path = stageDrvrPath(input_stage);
   if (input_path->isClock(this)) {
     const Clock *clk = input_path->clock(this);
     float period = clk->period();
@@ -258,7 +258,7 @@ WritePathSpice::pathMaxTime()
 {
   float max_time = 0.0;
   for (size_t i = 0; i < path_expanded_.size(); i++) {
-    PathRef *path = path_expanded_.path(i);
+    const PathRef *path = path_expanded_.path(i);
     const RiseFall *rf = path->transition(this);
     Vertex *vertex = path->vertex(this);
     float path_max_slew = railToRailSlew(findSlew(vertex,rf,nullptr), rf);
@@ -315,7 +315,7 @@ WritePathSpice::writeInputSource()
   streamPrint(spice_stream_, "**************\n\n");
 
   Stage input_stage = stageFirst();
-  PathRef *input_path = stageDrvrPath(input_stage);
+  const PathRef *input_path = stageDrvrPath(input_stage);
   if (input_path->isClock(this))
     writeClkWaveform();
   else
@@ -327,7 +327,7 @@ void
 WritePathSpice::writeInputWaveform()
 {
   Stage input_stage = stageFirst();
-  PathRef *input_path = stageDrvrPath(input_stage);
+  const PathRef *input_path = stageDrvrPath(input_stage);
   const RiseFall *rf = input_path->transition(this);
   TimingArc *next_arc = stageGateArc(input_stage + 1);
   float slew0 = findSlew(input_path, rf, next_arc);
@@ -352,7 +352,7 @@ void
 WritePathSpice::writeClkWaveform()
 {
   Stage input_stage = stageFirst();
-  PathRef *input_path = stageDrvrPath(input_stage);
+  const PathRef *input_path = stageDrvrPath(input_stage);
   TimingArc *next_arc = stageGateArc(input_stage + 1);
   const ClockEdge *clk_edge = input_path->clkEdge(this);
 
@@ -387,7 +387,7 @@ WritePathSpice::writeClkWaveform()
 }
 
 float
-WritePathSpice::findSlew(Path *path)
+WritePathSpice::findSlew(const Path *path)
 {
   Vertex *vertex = path->vertex(this);
   const RiseFall *rf = path->transition(this);
@@ -395,9 +395,9 @@ WritePathSpice::findSlew(Path *path)
 }
 
 float
-WritePathSpice::findSlew(Path *path,
-                     const RiseFall *rf,
-                     TimingArc *next_arc)
+WritePathSpice::findSlew(const Path *path,
+                         const RiseFall *rf,
+                         TimingArc *next_arc)
 {
   Vertex *vertex = path->vertex(this);
   return findSlew(vertex, rf, next_arc);
@@ -413,9 +413,9 @@ WritePathSpice::writeMeasureStmts()
   streamPrint(spice_stream_, "********************\n\n");
 
   for (Stage stage = stageFirst(); stage <= stageLast(); stage++) {
-    PathRef *gate_input_path = stageGateInputPath(stage);
-    PathRef *drvr_path = stageDrvrPath(stage);
-    PathRef *load_path = stageLoadPath(stage);
+    const PathRef *gate_input_path = stageGateInputPath(stage);
+    const PathRef *drvr_path = stageDrvrPath(stage);
+    const PathRef *load_path = stageLoadPath(stage);
     if (gate_input_path) {
       // gate input -> gate output
       writeMeasureSlewStmt(stage, gate_input_path);
@@ -432,8 +432,8 @@ WritePathSpice::writeMeasureStmts()
 
 void
 WritePathSpice::writeMeasureDelayStmt(Stage stage,
-				      Path *from_path,
-				      Path *to_path)
+				      const Path *from_path,
+				      const Path *to_path)
 {
   writeMeasureDelayStmt(from_path->pin(this), from_path->transition(this),
                         to_path->pin(this), to_path->transition(this),
@@ -442,7 +442,7 @@ WritePathSpice::writeMeasureDelayStmt(Stage stage,
 
 void
 WritePathSpice::writeMeasureSlewStmt(Stage stage,
-				     Path *path)
+				     const Path *path)
 {
   const Pin *pin = path->pin(this);
   const RiseFall *rf = path->transition(this);
@@ -514,7 +514,7 @@ WritePathSpice::writeGateStage(Stage stage)
 	      drvr_port->name());
   writeSubcktInst(inst);
 
-  PathRef *drvr_path = stageDrvrPath(stage);
+  const PathRef *drvr_path = stageDrvrPath(stage);
   const RiseFall *drvr_rf = drvr_path->transition(this);
   Edge *gate_edge = stageGateEdge(stage);
 
@@ -544,7 +544,7 @@ WritePathSpice::writeGateStage(Stage stage)
 void
 WritePathSpice::writeStageParasitics(Stage stage)
 {
-  PathRef *drvr_path = stageDrvrPath(stage);
+  const PathRef *drvr_path = stageDrvrPath(stage);
   DcalcAnalysisPt *dcalc_ap = drvr_path->dcalcAnalysisPt(this);
   ParasiticAnalysisPt *parasitic_ap = dcalc_ap->parasiticAnalysisPt();
   const Pin *drvr_pin = stageDrvrPin(stage);
@@ -637,21 +637,21 @@ WritePathSpice::stageLoadPathIndex(Stage stage)
   return stage * 2 - 1;
 }
 
-PathRef *
+const PathRef *
 WritePathSpice::stageGateInputPath(Stage stage)
 {
   int path_index = stageGateInputPathIndex(stage);
   return path_expanded_.path(path_index);
 }
 
-PathRef *
+const PathRef *
 WritePathSpice::stageDrvrPath(Stage stage)
 {
   int path_index = stageDrvrPathIndex(stage);
   return path_expanded_.path(path_index);
 }
 
-PathRef *
+const PathRef *
 WritePathSpice::stageLoadPath(Stage stage)
 {
   int path_index = stageLoadPathIndex(stage);
@@ -678,7 +678,7 @@ WritePathSpice::stageWireArc(Stage stage)
 Edge *
 WritePathSpice::stageGateEdge(Stage stage)
 {
-  PathRef *path = stageDrvrPath(stage);
+  const PathRef *path = stageDrvrPath(stage);
   TimingArc *arc = stageGateArc(stage);
   return path->prevEdge(arc, this);
 }
@@ -686,7 +686,7 @@ WritePathSpice::stageGateEdge(Stage stage)
 Edge *
 WritePathSpice::stageWireEdge(Stage stage)
 {
-  PathRef *path = stageLoadPath(stage);
+  const PathRef *path = stageLoadPath(stage);
   TimingArc *arc = stageWireArc(stage);
   return path->prevEdge(arc, this);
 }
@@ -694,7 +694,7 @@ WritePathSpice::stageWireEdge(Stage stage)
 Pin *
 WritePathSpice::stageGateInputPin(Stage stage)
 {
-  PathRef *path = stageGateInputPath(stage);
+  const PathRef *path = stageGateInputPath(stage);
   return path->pin(this);
 }
 
@@ -708,7 +708,7 @@ WritePathSpice::stageGateInputPort(Stage stage)
 Pin *
 WritePathSpice::stageDrvrPin(Stage stage)
 {
-  PathRef *path = stageDrvrPath(stage);
+  const PathRef *path = stageDrvrPath(stage);
   return path->pin(this);
 }
 
@@ -722,7 +722,7 @@ WritePathSpice::stageDrvrPort(Stage stage)
 Pin *
 WritePathSpice::stageLoadPin(Stage stage)
 {
-  PathRef *path = stageLoadPath(stage);
+  const PathRef *path = stageLoadPath(stage);
   return path->pin(this);
 }
 
diff --git a/tcl/Util.tcl b/tcl/Util.tcl
index 23b3ba00..f233bf47 100644
--- a/tcl/Util.tcl
+++ b/tcl/Util.tcl
@@ -341,21 +341,20 @@ proc sta_unknown { args } {
   }
   if { $ret != 0 } {
     return -code $ret -errorcode $errorCode \
-      "error in unknown while checking if \"$name\" is a unique command abbreviation: $msg"
+      "Error in unknown while checking if \"$name\" is a unique command abbreviation: $msg."
     }
   if { [llength $cmds] == 1 } {
     return [uplevel 1 [lreplace $args 0 0 $cmds]]
   }
   if { [llength $cmds] > 1 } {
     if {[string equal $name ""]} {
-      return -code error "empty command name \"\""
+      return -code error "Empty command name \"\""
     } else {
       return -code error \
-        "ambiguous command name \"$name\": [lsort $cmds]"
+        "Ambiguous command name \"$name\": [lsort $cmds]."
     }
   }
-
-  ::unknown {*}$args
+  return [uplevel 1 [::unknown {*}$args]]
 }
 
 proc is_bus_subscript { subscript } {
diff --git a/util/StringUtil.cc b/util/StringUtil.cc
index 659c06a4..02c5edfc 100644
--- a/util/StringUtil.cc
+++ b/util/StringUtil.cc
@@ -76,6 +76,20 @@ stringPrint(string &str,
   str = tmp;
 }
 
+void
+stringAppend(string &str,
+             const char *fmt,
+             ...)
+{
+  va_list args;
+  va_start(args, fmt);
+  char *tmp;
+  size_t tmp_length;
+  stringPrintTmp(fmt, args, tmp, tmp_length);
+  va_end(args);
+  str += tmp;
+}
+
 string
 stdstrPrint(const char *fmt,
 	    ...)