diff --git a/src/comm.cpp b/src/comm.cpp
index 5175af28e5..1679cc3c41 100644
--- a/src/comm.cpp
+++ b/src/comm.cpp
@@ -282,12 +282,12 @@ void Comm::init_exchange()
 
 void Comm::modify_params(int narg, char **arg)
 {
-  if (narg < 1) error->all(FLERR,"Illegal comm_modify command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "comm_modify", error);
 
   int iarg = 0;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"mode") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal comm_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "comm_modify mode", error);
       if (strcmp(arg[iarg+1],"single") == 0) {
         // need to reset cutghostuser when switching comm mode
         if (mode == Comm::MULTI) cutghostuser = 0.0;
@@ -311,26 +311,27 @@ void Comm::modify_params(int narg, char **arg)
         if (mode == Comm::MULTI) cutghostuser = 0.0;
         memory->destroy(cutusermulti);
         mode = Comm::MULTIOLD;
-      } else error->all(FLERR,"Illegal comm_modify command");
+      } else error->all(FLERR,"Unknown comm_modify mode argument: {}", arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"group") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal comm_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "comm_modify group", error);
       bordergroup = group->find(arg[iarg+1]);
       if (bordergroup < 0)
-        error->all(FLERR,"Invalid group in comm_modify command");
-      if (bordergroup && (atom->firstgroupname == nullptr ||
-                          strcmp(arg[iarg+1],atom->firstgroupname) != 0))
-        error->all(FLERR,"Comm_modify group != atom_modify first group");
+        error->all(FLERR, "Invalid comm_modify keyword: group {} not found", arg[iarg+1]);
+      if (atom->firstgroupname == nullptr)
+        error->all(FLERR, "Invalid comm_modify keyword: atom_modify first command must be used");
+      if (strcmp(arg[iarg+1],atom->firstgroupname) != 0)
+        error->all(FLERR, "comm_modify group != atom_modify first group: {}", atom->firstgroupname);
       iarg += 2;
     } else if (strcmp(arg[iarg],"cutoff") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal comm_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "comm_modify cutoff", error);
       if (mode == Comm::MULTI)
         error->all(FLERR, "Use cutoff/multi keyword to set cutoff in multi mode");
       if (mode == Comm::MULTIOLD)
         error->all(FLERR, "Use cutoff/multi/old keyword to set cutoff in multi mode");
       cutghostuser = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       if (cutghostuser < 0.0)
-        error->all(FLERR,"Invalid cutoff in comm_modify command");
+        error->all(FLERR,"Invalid cutoff {} in comm_modify command", arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"cutoff/multi") == 0) {
       int i,nlo,nhi;
@@ -355,7 +356,7 @@ void Comm::modify_params(int narg, char **arg)
       cut = utils::numeric(FLERR,arg[iarg+2],false,lmp);
       cutghostuser = MAX(cutghostuser,cut);
       if (cut < 0.0)
-        error->all(FLERR,"Invalid cutoff in comm_modify command");
+        error->all(FLERR,"Invalid cutoff {} in comm_modify command", arg[iarg+2]);
       // collections use 1-based indexing externally and 0-based indexing internally
       for (i=nlo; i<=nhi; ++i)
         cutusermulti[i-1] = cut;
@@ -370,8 +371,7 @@ void Comm::modify_params(int narg, char **arg)
       if (domain->box_exist == 0)
         error->all(FLERR, "Cannot set cutoff/multi before simulation box is defined");
       const int ntypes = atom->ntypes;
-      if (iarg+3 > narg)
-        error->all(FLERR,"Illegal comm_modify command");
+      if (iarg+3 > narg) utils::missing_cmd_args(FLERR, "comm_modify cutoff/multi/old", error);
       if (cutusermultiold == nullptr) {
         memory->create(cutusermultiold,ntypes+1,"comm:cutusermultiold");
         for (i=0; i < ntypes+1; ++i)
@@ -381,7 +381,7 @@ void Comm::modify_params(int narg, char **arg)
       cut = utils::numeric(FLERR,arg[iarg+2],false,lmp);
       cutghostuser = MAX(cutghostuser,cut);
       if (cut < 0.0)
-        error->all(FLERR,"Invalid cutoff in comm_modify command");
+        error->all(FLERR,"Invalid cutoff {} in comm_modify command", arg[iarg+2]);
       for (i=nlo; i<=nhi; ++i)
         cutusermultiold[i] = cut;
       iarg += 3;
@@ -391,10 +391,10 @@ void Comm::modify_params(int narg, char **arg)
       multi_reduce = 1;
       iarg += 1;
     } else if (strcmp(arg[iarg],"vel") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal comm_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "comm_modify vel", error);
       ghost_velocity = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
-    } else error->all(FLERR,"Illegal comm_modify command");
+    } else error->all(FLERR,"Unknown comm_modify keyword: {}", arg[iarg]);
   }
 }
 
diff --git a/src/domain.cpp b/src/domain.cpp
index d3d6985f99..4d299fb7bf 100644
--- a/src/domain.cpp
+++ b/src/domain.cpp
@@ -1744,7 +1744,7 @@ void Domain::set_lattice(int narg, char **arg)
 
 void Domain::add_region(int narg, char **arg)
 {
-  if (narg < 2) error->all(FLERR,"Illegal region command");
+  if (narg < 2) utils::missing_cmd_args(FLERR, "region", error);
 
   if (strcmp(arg[1],"delete") == 0) {
     delete_region(arg[0]);
@@ -1935,17 +1935,17 @@ void Domain::set_boundary(int narg, char **arg, int flag)
 
 void Domain::set_box(int narg, char **arg)
 {
-  if (narg < 1) error->all(FLERR,"Illegal box command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "box", error);
 
   int iarg = 0;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"tilt") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal box command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "box tilt", error);
       if (strcmp(arg[iarg+1],"small") == 0) tiltsmall = 1;
       else if (strcmp(arg[iarg+1],"large") == 0) tiltsmall = 0;
-      else error->all(FLERR,"Illegal box command");
+      else error->all(FLERR,"Unknown box tilt argument: {}", arg[iarg+1]);
       iarg += 2;
-    } else error->all(FLERR,"Illegal box command");
+    } else error->all(FLERR,"Unknown box keyword: {}", arg[iarg]);
   }
 }
 
diff --git a/src/region.cpp b/src/region.cpp
index 307513add6..d63fe25017 100644
--- a/src/region.cpp
+++ b/src/region.cpp
@@ -66,27 +66,27 @@ void Region::init()
 {
   if (xstr) {
     xvar = input->variable->find(xstr);
-    if (xvar < 0) error->all(FLERR, "Variable name for region does not exist");
+    if (xvar < 0) error->all(FLERR, "Variable {} for region does not exist", xstr);
     if (!input->variable->equalstyle(xvar))
-      error->all(FLERR, "Variable for region is invalid style");
+      error->all(FLERR, "Variable {} for region is invalid style", xstr);
   }
   if (ystr) {
     yvar = input->variable->find(ystr);
-    if (yvar < 0) error->all(FLERR, "Variable name for region does not exist");
+    if (yvar < 0) error->all(FLERR, "Variable {} for region does not exist", ystr);
     if (!input->variable->equalstyle(yvar))
-      error->all(FLERR, "Variable for region is not equal style");
+      error->all(FLERR, "Variable {} for region is not equal style", ystr);
   }
   if (zstr) {
     zvar = input->variable->find(zstr);
-    if (zvar < 0) error->all(FLERR, "Variable name for region does not exist");
+    if (zvar < 0) error->all(FLERR, "Variable {} for region does not exist", zstr);
     if (!input->variable->equalstyle(zvar))
-      error->all(FLERR, "Variable for region is not equal style");
+      error->all(FLERR, "Variable {} for region is not equal style", zstr);
   }
   if (tstr) {
     tvar = input->variable->find(tstr);
-    if (tvar < 0) error->all(FLERR, "Variable name for region does not exist");
+    if (tvar < 0) error->all(FLERR, "Variable {} for region does not exist", tstr);
     if (!input->variable->equalstyle(tvar))
-      error->all(FLERR, "Variable for region is not equal style");
+      error->all(FLERR, "Variable {} for region is not equal style", tstr);
   }
   vel_timestep = -1;
 }