diff --git a/common/kernel/command.cc b/common/kernel/command.cc
index dc178cd2..73c51228 100644
--- a/common/kernel/command.cc
+++ b/common/kernel/command.cc
@@ -404,6 +404,8 @@ po::options_description CommandHandler::getGeneralOptions()
                           "enable experimental timing-driven ripup in router (deprecated; use --tmg-ripup instead)");
 
     general.add_options()("router2-alt-weights", "use alternate router2 weights");
+    general.add_options()("router2-heuristic-test", po::value<std::string>(),
+                          "write heuristic vs congestion-free delay data in CSV format to file");
 
     general.add_options()("report", po::value<std::string>(),
                           "write timing and utilization report in JSON format to file");
@@ -546,6 +548,9 @@ void CommandHandler::setupContext(Context *ctx)
     if (vm.count("router2-alt-weights"))
         ctx->settings[ctx->id("router2/alt-weights")] = true;
 
+    if (vm.count("router2-heuristic-test"))
+        ctx->settings[ctx->id("router2/heuristic-test")] = vm["router2-heuristic-test"].as<std::string>();
+
     if (vm.count("static-dump-density"))
         ctx->settings[ctx->id("static/dump_density")] = true;
 
diff --git a/common/route/router2.cc b/common/route/router2.cc
index 8dcec6e9..b2b8d6b8 100644
--- a/common/route/router2.cc
+++ b/common/route/router2.cc
@@ -1373,6 +1373,13 @@ struct Router2
 
     void update_route_delays()
     {
+        std::ofstream f;
+        if (!cfg.heuristic_test.empty()) {
+            f.open(cfg.heuristic_test);
+            if (!f)
+                log_error("Failed to open heuristic test output file %s for writing.\n", cfg.heuristic_test.c_str());
+            f << "source wire,sink wire,heuristic delay (ns),actual delay (ns)" << std::endl;
+        }
         for (int net : route_queue) {
             NetInfo *ni = nets_by_udata.at(net);
 #ifdef ARCH_ECP5
@@ -1382,8 +1389,16 @@ struct Router2
             auto &nd = nets.at(net);
             for (auto usr : ni->users.enumerate()) {
                 delay_t arc_delay = 0;
-                for (int j = 0; j < int(nd.arcs.at(usr.index.idx()).size()); j++)
-                    arc_delay = std::max(arc_delay, get_route_delay(net, usr.index, j));
+                for (int j = 0; j < int(nd.arcs.at(usr.index.idx()).size()); j++) {
+                    delay_t route_delay = get_route_delay(net, usr.index, j);
+                    if (f) {
+                        auto src_wire = nd.src_wire;
+                        auto sink_wire = nd.arcs.at(usr.index.idx()).at(j).sink_wire;
+                        if (src_wire != WireId() && sink_wire != WireId())
+                            f << ctx->nameOfWire(src_wire) << "," << ctx->nameOfWire(sink_wire) << "," << ctx->getDelayNS(ctx->estimateDelay(src_wire, sink_wire)) << "," << ctx->getDelayNS(route_delay) << std::endl;
+                    }
+                    arc_delay = std::max(arc_delay, route_delay);
+                }
                 tmg.set_route_delay(CellPortKey(usr.value), DelayPair(arc_delay));
             }
         }
@@ -1446,6 +1461,9 @@ struct Router2
                 write_wiretype_heatmap(cong_map);
                 log_info("        wrote wiretype heatmap to %s.\n", filename.c_str());
             }
+
+            NPNR_ASSERT_MSG(cfg.heuristic_test.empty(), "congestion-free routing complete; nextpnr will exit now");
+
             int tmgfail = 0;
             if (timing_driven)
                 tmg.run(false);
@@ -1523,6 +1541,12 @@ Router2Cfg::Router2Cfg(Context *ctx)
         hist_cong_weight = ctx->setting<float>("router2/histCongWeight", 0.5f);
         curr_cong_mult = ctx->setting<float>("router2/currCongWeightMult", 0.0f);
         estimate_weight = ctx->setting<float>("router2/estimateWeight", 1.0f);
+    } else if (ctx->settings.count(ctx->id("router2/heuristic-test"))) {
+        init_curr_cong_weight = 0.0f;
+        hist_cong_weight = 0.0f;
+        curr_cong_mult = 0.0f;
+        estimate_weight = 1.25f;
+        heuristic_test = ctx->settings.at(ctx->id("router2/heuristic-test")).as_string();
     } else {
         init_curr_cong_weight = ctx->setting<float>("router2/initCurrCongWeight", 0.5f);
         hist_cong_weight = ctx->setting<float>("router2/histCongWeight", 1.0f);
diff --git a/common/route/router2.h b/common/route/router2.h
index 629453c6..e9c43d21 100644
--- a/common/route/router2.h
+++ b/common/route/router2.h
@@ -57,6 +57,8 @@ struct Router2Cfg
     // Print additional performance profiling information
     bool perf_profile = false;
 
+    std::string heuristic_test;
+
     std::string heatmap;
     std::function<float(Context *ctx, WireId wire, PipId pip, float crit_weight)> get_base_cost = default_base_cost;
 };
diff --git a/python/plot_heuristic.py b/python/plot_heuristic.py
new file mode 100644
index 00000000..873e7ff0
--- /dev/null
+++ b/python/plot_heuristic.py
@@ -0,0 +1,32 @@
+import matplotlib.pyplot as plt
+import csv
+
+RED = '#ca684d'
+GREEN = '#7aa354'
+BLUE = '#5e84d0'
+
+EPSILON = 0.02
+
+heuristic = []
+actual = []
+color = []
+with open('heuristic.csv') as f:
+    reader = csv.reader(f, delimiter=',')
+    rows = [row for row in reader]
+    for row in rows[1:]:
+        heuristic_value = float(row[2])
+        actual_value = float(row[3])
+        heuristic.append(heuristic_value)
+        actual.append(actual_value)
+        if heuristic_value > actual_value+EPSILON:
+            color.append(RED)
+        elif heuristic_value < actual_value-EPSILON:
+            color.append(BLUE)
+        else:
+            color.append(GREEN)
+
+plt.scatter(actual, heuristic, c=color)
+plt.xlabel("Actual Delay (ns)")
+plt.ylabel("Estimated Delay (ns)")
+plt.savefig("heuristic_vs_actual.png")
+