diff --git a/common/kernel/arch_api.h b/common/kernel/arch_api.h
index 94a88338..56c5cf0a 100644
--- a/common/kernel/arch_api.h
+++ b/common/kernel/arch_api.h
@@ -135,7 +135,7 @@ template <typename R> struct ArchAPI : BaseCtx
     virtual BelBucketId getBelBucketByName(IdString name) const = 0;
     virtual BelBucketId getBelBucketForBel(BelId bel) const = 0;
     virtual BelBucketId getBelBucketForCellType(IdString cell_type) const = 0;
-    virtual bool isBelLocationValid(BelId bel) const = 0;
+    virtual bool isBelLocationValid(BelId bel, bool explain_invalid = false) const = 0;
     virtual typename R::CellTypeRangeT getCellTypes() const = 0;
     virtual typename R::BelBucketRangeT getBelBuckets() const = 0;
     virtual typename R::BucketBelRangeT getBelsInBucket(BelBucketId bucket) const = 0;
diff --git a/common/kernel/arch_pybindings_shared.h b/common/kernel/arch_pybindings_shared.h
index d78d240c..ac0eda07 100644
--- a/common/kernel/arch_pybindings_shared.h
+++ b/common/kernel/arch_pybindings_shared.h
@@ -127,8 +127,8 @@ fn_wrapper_0a<Context, decltype(&Context::archId), &Context::archId, conv_to_str
 fn_wrapper_2a_v<Context, decltype(&Context::writeSVG), &Context::writeSVG, pass_through<std::string>,
                 pass_through<std::string>>::def_wrap(ctx_cls, "writeSVG");
 
-fn_wrapper_1a<Context, decltype(&Context::isBelLocationValid), &Context::isBelLocationValid, pass_through<bool>,
-              conv_from_str<BelId>>::def_wrap(ctx_cls, "isBelLocationValid");
+fn_wrapper_2a<Context, decltype(&Context::isBelLocationValid), &Context::isBelLocationValid, pass_through<bool>,
+              conv_from_str<BelId>, pass_through<bool>>::def_wrap(ctx_cls, "isBelLocationValid");
 
 // const\_range\<BelBucketId\> getBelBuckets() const
 fn_wrapper_0a<Context, decltype(&Context::getBelBuckets), &Context::getBelBuckets,
diff --git a/common/kernel/base_arch.h b/common/kernel/base_arch.h
index 53e28652..609d9378 100644
--- a/common/kernel/base_arch.h
+++ b/common/kernel/base_arch.h
@@ -357,7 +357,7 @@ template <typename R> struct BaseArch : ArchAPI<R>
     {
         return getBelBucketByName(cell_type);
     };
-    virtual bool isBelLocationValid(BelId bel) const override { return true; }
+    virtual bool isBelLocationValid(BelId bel, bool explain_invalid = false) const override { return true; }
     virtual typename R::CellTypeRangeT getCellTypes() const override
     {
         NPNR_ASSERT(cell_types_initialised);
diff --git a/common/place/placer1.cc b/common/place/placer1.cc
index 23264ce2..e37d3daf 100644
--- a/common/place/placer1.cc
+++ b/common/place/placer1.cc
@@ -173,7 +173,7 @@ class SAPlacer
                     }
 
                     ctx->bindBel(bel, cell, STRENGTH_USER);
-                    if (!ctx->isBelLocationValid(bel)) {
+                    if (!ctx->isBelLocationValid(bel, /* explain_invalid */ true)) {
                         IdString bel_type = ctx->getBelType(bel);
                         log_error("Bel \'%s\' of type \'%s\' is not valid for cell "
                                   "\'%s\' of type \'%s\'\n",
@@ -404,7 +404,7 @@ class SAPlacer
         ctx->yield();
         for (auto bel : ctx->getBels()) {
             CellInfo *cell = ctx->getBoundBelCell(bel);
-            if (!ctx->isBelLocationValid(bel)) {
+            if (!ctx->isBelLocationValid(bel, /* explain_invalid */ true)) {
                 std::string cell_text = "no cell";
                 if (cell != nullptr)
                     cell_text = std::string("cell '") + ctx->nameOf(cell) + "'";
diff --git a/common/place/placer_heap.cc b/common/place/placer_heap.cc
index 8da4ee2e..0dfc29e6 100644
--- a/common/place/placer_heap.cc
+++ b/common/place/placer_heap.cc
@@ -327,7 +327,7 @@ class HeAPPlacer
         bool any_bad_placements = false;
         for (auto bel : ctx->getBels()) {
             CellInfo *cell = ctx->getBoundBelCell(bel);
-            if (!ctx->isBelLocationValid(bel)) {
+            if (!ctx->isBelLocationValid(bel, /* explain_invalid */ true)) {
                 std::string cell_text = "no cell";
                 if (cell != nullptr)
                     cell_text = std::string("cell '") + ctx->nameOf(cell) + "'";
@@ -434,7 +434,7 @@ class HeAPPlacer
                 }
 
                 ctx->bindBel(bel, cell, STRENGTH_USER);
-                if (!ctx->isBelLocationValid(bel)) {
+                if (!ctx->isBelLocationValid(bel, /* explain_invalid */ true)) {
                     IdString bel_type = ctx->getBelType(bel);
                     log_error("Bel \'%s\' of type \'%s\' is not valid for cell "
                               "\'%s\' of type \'%s\'\n",
diff --git a/docs/archapi.md b/docs/archapi.md
index 39b2a6a9..3a7994de 100644
--- a/docs/archapi.md
+++ b/docs/archapi.md
@@ -698,11 +698,15 @@ return the same value regardless if other cells are placed within the fabric.
 
 *BaseArch default: returns `cell_type == getBelType(bel)`*
 
-### bool isBelLocationValid(BelId bel) const
+### bool isBelLocationValid(BelId bel, bool explain_invalid = false) const
 
 Returns true if a bel in the current configuration is legal (for example,
 a flipflop's clock signal is correctly shared with all bels in a slice.)
 
+If and only if `explain_invalid` is set to true, then a message using
+`log_nonfatal_error` should be printed explaining why the placement is invalid
+to the end user.
+
 *BaseArch default: returns true*
 
 ### static const std::string defaultPlacer
diff --git a/docs/viaduct.md b/docs/viaduct.md
index a59310f1..88398a05 100644
--- a/docs/viaduct.md
+++ b/docs/viaduct.md
@@ -64,7 +64,7 @@ X(F)
 ```c++
 bool checkBelAvail(BelId bel) const;
 bool isValidBelForCellType(IdString cell_type, BelId bel) const;
-bool isBelLocationValid(BelId bel) const;
+bool isBelLocationValid(BelId bel, bool explain_invalid = false) const;
 bool checkWireAvail(WireId wire) const;
 bool checkPipAvail(PipId pip) const;
 bool checkPipAvailForNet(PipId pip, NetInfo *net) const;
diff --git a/ecp5/arch.h b/ecp5/arch.h
index a40719c1..6ce3c4ce 100644
--- a/ecp5/arch.h
+++ b/ecp5/arch.h
@@ -1010,7 +1010,7 @@ struct Arch : BaseArch<ArchRanges>
 
     // -------------------------------------------------
     // Placement validity checks
-    bool isBelLocationValid(BelId bel) const override;
+    bool isBelLocationValid(BelId bel, bool explain_invalid = false) const override;
 
     // Helper function for above
     bool slices_compatible(LogicTileStatus *lts) const;
diff --git a/ecp5/arch_place.cc b/ecp5/arch_place.cc
index fed9c055..3151cc3e 100644
--- a/ecp5/arch_place.cc
+++ b/ecp5/arch_place.cc
@@ -178,7 +178,7 @@ bool Arch::slices_compatible(LogicTileStatus *lts) const
     return true;
 }
 
-bool Arch::isBelLocationValid(BelId bel) const
+bool Arch::isBelLocationValid(BelId bel, bool explain_invalid) const
 {
     IdString bel_type = getBelType(bel);
     if (bel_type.in(id_TRELLIS_COMB, id_TRELLIS_FF, id_TRELLIS_RAMW)) {
diff --git a/fpga_interchange/arch.h b/fpga_interchange/arch.h
index 7e373a56..a44c7c21 100644
--- a/fpga_interchange/arch.h
+++ b/fpga_interchange/arch.h
@@ -851,7 +851,7 @@ struct Arch : ArchAPI<ArchRanges>
     }
 
     // Return true whether all Bels at a given location are valid
-    bool isBelLocationValid(BelId bel) const final
+    bool isBelLocationValid(BelId bel, bool explain_invalid = false) const final
     {
         auto iter = tileStatus.find(bel.tile);
         if (iter == tileStatus.end()) {
diff --git a/generic/arch.cc b/generic/arch.cc
index c60c7674..579140b9 100644
--- a/generic/arch.cc
+++ b/generic/arch.cc
@@ -693,10 +693,10 @@ TimingClockingInfo Arch::getPortClockingInfo(const CellInfo *cell, IdString port
     return tmg.clockingInfo.at(port).at(index);
 }
 
-bool Arch::isBelLocationValid(BelId bel) const
+bool Arch::isBelLocationValid(BelId bel, bool explain_invalid) const
 {
     if (uarch)
-        return uarch->isBelLocationValid(bel);
+        return uarch->isBelLocationValid(bel, explain_invalid);
     std::vector<const CellInfo *> cells;
     Loc loc = getBelLocation(bel);
     for (auto tbel : getBelsByTile(loc.x, loc.y)) {
diff --git a/generic/arch.h b/generic/arch.h
index a27dc78e..2a177be9 100644
--- a/generic/arch.h
+++ b/generic/arch.h
@@ -386,7 +386,7 @@ struct Arch : BaseArch<ArchRanges>
     {
         return uarch ? uarch->isValidBelForCellType(cell_type, bel) : cell_type == getBelType(bel);
     }
-    bool isBelLocationValid(BelId bel) const override;
+    bool isBelLocationValid(BelId bel, bool explain_invalid = false) const override;
 
     static const std::string defaultPlacer;
     static const std::vector<std::string> availablePlacers;
diff --git a/generic/viaduct/example/example.cc b/generic/viaduct/example/example.cc
index 987c3236..7a61a594 100644
--- a/generic/viaduct/example/example.cc
+++ b/generic/viaduct/example/example.cc
@@ -62,7 +62,7 @@ struct ExampleImpl : ViaductAPI
 
     void prePlace() override { assign_cell_info(); }
 
-    bool isBelLocationValid(BelId bel) const override
+    bool isBelLocationValid(BelId bel, bool explain_invalid) const override
     {
         Loc l = ctx->getBelLocation(bel);
         if (is_io(l.x, l.y)) {
diff --git a/generic/viaduct/fabulous/fabulous.cc b/generic/viaduct/fabulous/fabulous.cc
index 3c6f025f..e2fe1b74 100644
--- a/generic/viaduct/fabulous/fabulous.cc
+++ b/generic/viaduct/fabulous/fabulous.cc
@@ -81,7 +81,10 @@ struct FabulousImpl : ViaductAPI
     }
 
     void prePlace() override { assign_cell_info(); }
-    bool isBelLocationValid(BelId bel) const override { return blk_trk->check_validity(bel, cfg, cell_tags); }
+    bool isBelLocationValid(BelId bel, bool explain_invalid) const override
+    {
+        return blk_trk->check_validity(bel, cfg, cell_tags);
+    }
 
   private:
     FabricConfig cfg; // TODO: non-default config
diff --git a/generic/viaduct/okami/okami.cc b/generic/viaduct/okami/okami.cc
index 8142756f..4ff97cb3 100644
--- a/generic/viaduct/okami/okami.cc
+++ b/generic/viaduct/okami/okami.cc
@@ -64,7 +64,7 @@ struct OkamiImpl : ViaductAPI
 
     void prePlace() override { assign_cell_info(); }
 
-    bool isBelLocationValid(BelId bel) const override
+    bool isBelLocationValid(BelId bel, bool explain_invalid) const override
     {
         Loc l = ctx->getBelLocation(bel);
         if (is_io(l.x, l.y)) {
diff --git a/generic/viaduct_api.h b/generic/viaduct_api.h
index 6887f56c..3caa0ba1 100644
--- a/generic/viaduct_api.h
+++ b/generic/viaduct_api.h
@@ -67,7 +67,7 @@ struct ViaductAPI
     virtual BelBucketId getBelBucketForBel(BelId bel) const;
     virtual BelBucketId getBelBucketForCellType(IdString cell_type) const;
     virtual bool isValidBelForCellType(IdString cell_type, BelId bel) const;
-    virtual bool isBelLocationValid(BelId bel) const { return true; }
+    virtual bool isBelLocationValid(BelId bel, bool explain_invalid = false) const { return true; }
 
     // --- Wire and pip functions ---
     // Called when a wire/pip is placed/unplaced (with net=nullptr for a unbind)
diff --git a/gowin/arch.cc b/gowin/arch.cc
index 05b09363..28c0cb1e 100644
--- a/gowin/arch.cc
+++ b/gowin/arch.cc
@@ -2028,7 +2028,7 @@ TimingClockingInfo Arch::getPortClockingInfo(const CellInfo *cell, IdString port
     return tmg.clockingInfo.at(port).at(index);
 }
 
-bool Arch::isBelLocationValid(BelId bel) const
+bool Arch::isBelLocationValid(BelId bel, bool explain_invalid) const
 {
     Loc loc = getBelLocation(bel);
 
diff --git a/gowin/arch.h b/gowin/arch.h
index 231fae6e..a929ef00 100644
--- a/gowin/arch.h
+++ b/gowin/arch.h
@@ -458,7 +458,7 @@ struct Arch : BaseArch<ArchRanges>
     // Get the TimingClockingInfo of a port
     TimingClockingInfo getPortClockingInfo(const CellInfo *cell, IdString port, int index) const override;
 
-    bool isBelLocationValid(BelId bel) const override;
+    bool isBelLocationValid(BelId bel, bool explain_invalid = false) const override;
 
     static const std::string defaultPlacer;
     static const std::vector<std::string> availablePlacers;
diff --git a/ice40/arch.h b/ice40/arch.h
index 9d10cddf..d80d6f64 100644
--- a/ice40/arch.h
+++ b/ice40/arch.h
@@ -840,7 +840,7 @@ struct Arch : BaseArch<ArchRanges>
     // implemented in arch_place.cc)
 
     // Return true whether all Bels at a given location are valid
-    bool isBelLocationValid(BelId bel) const override;
+    bool isBelLocationValid(BelId bel, bool explain_invalid = false) const override;
 
     // Helper function for above
     bool logic_cells_compatible(const CellInfo **it, const size_t size) const;
diff --git a/ice40/arch_place.cc b/ice40/arch_place.cc
index 5c3fa3c5..d8232571 100644
--- a/ice40/arch_place.cc
+++ b/ice40/arch_place.cc
@@ -82,7 +82,7 @@ static inline bool _io_pintype_need_clk_en(unsigned pin_type)
     return _io_pintype_need_clk_in(pin_type) || _io_pintype_need_clk_out(pin_type);
 }
 
-bool Arch::isBelLocationValid(BelId bel) const
+bool Arch::isBelLocationValid(BelId bel, bool explain_invalid) const
 {
     if (getBelType(bel) == id_ICESTORM_LC) {
         std::array<const CellInfo *, 8> bel_cells;
diff --git a/machxo2/arch.cc b/machxo2/arch.cc
index 93eb4e60..d85921bc 100644
--- a/machxo2/arch.cc
+++ b/machxo2/arch.cc
@@ -451,7 +451,7 @@ bool Arch::route()
 
 // ---------------------------------------------------------------
 
-bool Arch::isBelLocationValid(BelId bel) const
+bool Arch::isBelLocationValid(BelId bel, bool explain_invalid) const
 {
     // FIXME: Same deal as isValidBelForCell.
     return true;
diff --git a/machxo2/arch.h b/machxo2/arch.h
index ddcb9264..489a44ab 100644
--- a/machxo2/arch.h
+++ b/machxo2/arch.h
@@ -643,7 +643,7 @@ struct Arch : BaseArch<ArchRanges>
     bool route() override;
 
     // Placer
-    bool isBelLocationValid(BelId bel) const override;
+    bool isBelLocationValid(BelId bel, bool explain_invalid = false) const override;
 
     static const std::string defaultPlacer;
     static const std::vector<std::string> availablePlacers;
diff --git a/mistral/arch.cc b/mistral/arch.cc
index ce4f93fb..f3e385d1 100644
--- a/mistral/arch.cc
+++ b/mistral/arch.cc
@@ -182,7 +182,7 @@ IdStringList Arch::getBelName(BelId bel) const
     return IdStringList(ids);
 }
 
-bool Arch::isBelLocationValid(BelId bel) const
+bool Arch::isBelLocationValid(BelId bel, bool explain_invalid) const
 {
     auto &data = bel_data(bel);
     if (data.type.in(id_MISTRAL_COMB, id_MISTRAL_MCOMB)) {
diff --git a/mistral/arch.h b/mistral/arch.h
index 54a39771..aabe10c6 100644
--- a/mistral/arch.h
+++ b/mistral/arch.h
@@ -333,7 +333,7 @@ struct Arch : BaseArch<ArchRanges>
     PortType getBelPinType(BelId bel, IdString pin) const override { return bel_data(bel).pins.at(pin).dir; }
     std::vector<IdString> getBelPins(BelId bel) const override;
 
-    bool isBelLocationValid(BelId bel) const override;
+    bool isBelLocationValid(BelId bel, bool explain_invalid = false) const override;
 
     void bindBel(BelId bel, CellInfo *cell, PlaceStrength strength) override
     {
diff --git a/nexus/arch.h b/nexus/arch.h
index 5ac16f28..eb3059a5 100644
--- a/nexus/arch.h
+++ b/nexus/arch.h
@@ -1322,7 +1322,7 @@ struct Arch : BaseArch<ArchRanges>
     // implemented in arch_place.cc)
 
     // Return true whether all Bels at a given location are valid
-    bool isBelLocationValid(BelId bel) const override;
+    bool isBelLocationValid(BelId bel, bool explain_invalid = false) const override;
 
     // -------------------------------------------------
 
diff --git a/nexus/arch_place.cc b/nexus/arch_place.cc
index 7b2c08ee..0bed30b4 100644
--- a/nexus/arch_place.cc
+++ b/nexus/arch_place.cc
@@ -96,7 +96,7 @@ bool Arch::nexus_logic_tile_valid(LogicTileStatus &lts) const
     return true;
 }
 
-bool Arch::isBelLocationValid(BelId bel) const
+bool Arch::isBelLocationValid(BelId bel, bool explain_invalid) const
 {
     if (bel_tile_is(bel, LOC_LOGIC)) {
         LogicTileStatus *lts = tileStatus[bel.tile].lts;