diff --git a/src/run.cpp b/src/run.cpp
index a026580c83..3a9a4dc32e 100644
--- a/src/run.cpp
+++ b/src/run.cpp
@@ -36,7 +36,7 @@ Run::Run(LAMMPS *lmp) : Command(lmp) {}
 
 void Run::command(int narg, char **arg)
 {
-  if (narg < 1) error->all(FLERR,"Illegal run command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "run", error);
 
   if (domain->box_exist == 0)
     error->all(FLERR,"Run command before simulation box is defined");
@@ -62,25 +62,25 @@ void Run::command(int narg, char **arg)
   int iarg = 1;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"upto") == 0) {
-      if (iarg+1 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+1 > narg) utils::missing_cmd_args(FLERR, "run upto", error);
       uptoflag = 1;
       iarg += 1;
     } else if (strcmp(arg[iarg],"start") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "run start", error);
       startflag = 1;
       start = utils::bnumeric(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"stop") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "run stop", error);
       stopflag = 1;
       stop = utils::bnumeric(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"pre") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "run pre", error);
       preflag = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"post") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "run post", error);
       postflag = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
 
@@ -89,15 +89,15 @@ void Run::command(int narg, char **arg)
       // set ncommands = 0 if single command and it is "NULL"
 
     } else if (strcmp(arg[iarg],"every") == 0) {
-      if (iarg+3 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+3 > narg) utils::missing_cmd_args(FLERR, "run every", error);
       nevery = utils::inumeric(FLERR,arg[iarg+1],false,lmp);
-      if (nevery <= 0) error->all(FLERR,"Illegal run command");
+      if (nevery <= 0) error->all(FLERR, "Invalid run every argument: {}", nevery);
       first = iarg+2;
       last = narg-1;
       ncommands = last-first + 1;
       if (ncommands == 1 && strcmp(arg[first],"NULL") == 0) ncommands = 0;
       iarg = narg;
-    } else error->all(FLERR,"Illegal run command");
+    } else error->all(FLERR,"Unknown run keyword: {}", arg[iarg]);
   }
 
   // set nsteps as integer, using upto value if specified
@@ -105,12 +105,12 @@ void Run::command(int narg, char **arg)
   int nsteps;
   if (!uptoflag) {
     if (nsteps_input < 0 || nsteps_input > MAXSMALLINT)
-      error->all(FLERR,"Invalid run command N value");
+      error->all(FLERR,"Invalid run command N value: {}", nsteps_input);
     nsteps = static_cast<int> (nsteps_input);
   } else {
     bigint delta = nsteps_input - update->ntimestep;
     if (delta < 0 || delta > MAXSMALLINT)
-      error->all(FLERR,"Invalid run command upto value");
+      error->all(FLERR,"Invalid run command upto value: {}", delta);
     nsteps = static_cast<int> (delta);
   }
 
@@ -118,13 +118,13 @@ void Run::command(int narg, char **arg)
 
   if (startflag) {
     if (start < 0)
-      error->all(FLERR,"Invalid run command start/stop value");
+      error->all(FLERR,"Invalid run command start value: {}", start);
     if (start > update->ntimestep)
       error->all(FLERR,"Run command start value is after start of run");
   }
   if (stopflag) {
     if (stop < 0)
-      error->all(FLERR,"Invalid run command start/stop value");
+      error->all(FLERR,"Invalid run command stop value: {}", stop);
     if (stop < update->ntimestep + nsteps)
       error->all(FLERR,"Run command stop value is before end of run");
   }
diff --git a/src/variable.cpp b/src/variable.cpp
index a564847b68..d6eec9eeb3 100644
--- a/src/variable.cpp
+++ b/src/variable.cpp
@@ -162,7 +162,7 @@ Variable::~Variable()
 
 void Variable::set(int narg, char **arg)
 {
-  if (narg < 2) error->all(FLERR,"Illegal variable command");
+  if (narg < 2) utils::missing_cmd_args(FLERR, "variable", error);
 
   int replaceflag = 0;
 
@@ -170,7 +170,7 @@ void Variable::set(int narg, char **arg)
   // doesn't matter if variable no longer exists
 
   if (strcmp(arg[1],"delete") == 0) {
-    if (narg != 2) error->all(FLERR,"Illegal variable command");
+    if (narg != 2) error->all(FLERR,"Illegal variable command: expected 2 argument but found {}", narg);
     if (find(arg[0]) >= 0) remove(find(arg[0]));
     return;
 
@@ -178,7 +178,7 @@ void Variable::set(int narg, char **arg)
   // num = listed args, which = 1st value, data = copied args
 
   } else if (strcmp(arg[1],"index") == 0) {
-    if (narg < 3) error->all(FLERR,"Illegal variable command");
+    if (narg < 3) utils::missing_cmd_args(FLERR, "variable index", error);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = INDEX;
@@ -193,6 +193,7 @@ void Variable::set(int narg, char **arg)
   // 2 args + pad: num = N2, which = N1, data = single string
 
   } else if (strcmp(arg[1],"loop") == 0) {
+    if (narg < 3) utils::missing_cmd_args(FLERR, "variable loop", error);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = LOOP;
@@ -200,7 +201,7 @@ void Variable::set(int narg, char **arg)
     if (narg == 3 || (narg == 4 && strcmp(arg[3],"pad") == 0)) {
       nfirst = 1;
       nlast = utils::inumeric(FLERR,arg[2],false,lmp);
-      if (nlast <= 0) error->all(FLERR,"Illegal variable command");
+      if (nlast <= 0) error->all(FLERR, "Invalid variable loop argument: {}", nlast);
       if (narg == 4 && strcmp(arg[3],"pad") == 0) {
         pad[nvar] = fmt::format("{}",nlast).size();
       } else pad[nvar] = 0;
@@ -208,11 +209,11 @@ void Variable::set(int narg, char **arg)
       nfirst = utils::inumeric(FLERR,arg[2],false,lmp);
       nlast = utils::inumeric(FLERR,arg[3],false,lmp);
       if (nfirst > nlast || nlast < 0)
-        error->all(FLERR,"Illegal variable command");
+        error->all(FLERR,"Illegal variable loop command: {} > {}", nfirst,nlast);
       if (narg == 5 && strcmp(arg[4],"pad") == 0) {
         pad[nvar] = fmt::format("{}",nlast).size();
       } else pad[nvar] = 0;
-    } else error->all(FLERR,"Illegal variable command");
+    } else error->all(FLERR,"Illegal variable loop command: too much arguments");
     num[nvar] = nlast;
     which[nvar] = nfirst-1;
     data[nvar] = new char*[1];
@@ -223,7 +224,7 @@ void Variable::set(int narg, char **arg)
   // error check that num = # of worlds in universe
 
   } else if (strcmp(arg[1],"world") == 0) {
-    if (narg < 3) error->all(FLERR,"Illegal variable command");
+    if (narg < 3) utils::missing_cmd_args(FLERR, "variable world", error);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = WORLD;
@@ -244,7 +245,7 @@ void Variable::set(int narg, char **arg)
 
   } else if (strcmp(arg[1],"universe") == 0 || strcmp(arg[1],"uloop") == 0) {
     if (strcmp(arg[1],"universe") == 0) {
-      if (narg < 3) error->all(FLERR,"Illegal variable command");
+      if (narg < 3) utils::missing_cmd_args(FLERR, "variable universe", error);
       if (find(arg[0]) >= 0) return;
       if (nvar == maxvar) grow();
       style[nvar] = UNIVERSE;
@@ -253,8 +254,10 @@ void Variable::set(int narg, char **arg)
       data[nvar] = new char*[num[nvar]];
       copy(num[nvar],&arg[2],data[nvar]);
     } else if (strcmp(arg[1],"uloop") == 0) {
-      if (narg < 3 || narg > 4 || (narg == 4 && strcmp(arg[3],"pad") != 0))
-        error->all(FLERR,"Illegal variable command");
+      if (narg < 3 || narg > 4)
+        error->all(FLERR,"Illegal variable command: expected 3 or 4 arguments but found {}", narg);
+      if (narg == 4 && strcmp(arg[3],"pad") != 0)
+        error->all(FLERR, "Invalid variable uloop argument: {}", arg[3]);
       if (find(arg[0]) >= 0) return;
       if (nvar == maxvar) grow();
       style[nvar] = ULOOP;
@@ -292,7 +295,7 @@ void Variable::set(int narg, char **arg)
   // data = 1 value, string to eval
 
   } else if (strcmp(arg[1],"string") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
 
     int maxcopy = strlen(arg[2]) + 1;
     int maxwork = maxcopy;
@@ -326,7 +329,7 @@ void Variable::set(int narg, char **arg)
   // data = 1 value, string to eval
 
   } else if (strcmp(arg[1],"getenv") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     if (find(arg[0]) >= 0) {
       if (style[find(arg[0])] != GETENV)
         error->all(FLERR,"Cannot redefine variable as a different style");
@@ -346,7 +349,7 @@ void Variable::set(int narg, char **arg)
   // data = 1 value, string to eval
 
   } else if (strcmp(arg[1],"file") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = SCALARFILE;
@@ -364,7 +367,7 @@ void Variable::set(int narg, char **arg)
   // data = nullptr
 
   } else if (strcmp(arg[1],"atomfile") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = ATOMFILE;
@@ -384,7 +387,7 @@ void Variable::set(int narg, char **arg)
   //   3rd is filled on retrieval
 
   } else if (strcmp(arg[1],"format") == 0) {
-    if (narg != 4) error->all(FLERR,"Illegal variable command");
+    if (narg != 4) error->all(FLERR,"Illegal variable command: expected 4 arguments but found {}", narg);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = FORMAT;
@@ -404,7 +407,7 @@ void Variable::set(int narg, char **arg)
   // data = 2 values, 1st is string to eval, 2nd is filled on retrieval
 
   } else if (strcmp(arg[1],"equal") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     int ivar = find(arg[0]);
     if (ivar >= 0) {
       if (style[ivar] != EQUAL)
@@ -430,7 +433,7 @@ void Variable::set(int narg, char **arg)
   // data = 1 value, string to eval
 
   } else if (strcmp(arg[1],"atom") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     int ivar = find(arg[0]);
     if (ivar >= 0) {
       if (style[ivar] != ATOM)
@@ -454,7 +457,7 @@ void Variable::set(int narg, char **arg)
   // data = 1 value, string to eval
 
   } else if (strcmp(arg[1],"vector") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     int ivar = find(arg[0]);
     if (ivar >= 0) {
       if (style[ivar] != VECTOR)
@@ -478,7 +481,7 @@ void Variable::set(int narg, char **arg)
   // data = 2 values, 1st is Python func to invoke, 2nd is filled by invoke
 
   } else if (strcmp(arg[1],"python") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     if (!python->is_enabled())
       error->all(FLERR,"LAMMPS is not built with Python embedded");
     int ivar = find(arg[0]);
@@ -507,7 +510,7 @@ void Variable::set(int narg, char **arg)
   // dvalue = numeric initialization via platform::walltime()
 
   } else if (strcmp(arg[1],"timer") == 0) {
-    if (narg != 2) error->all(FLERR,"Illegal variable command");
+    if (narg != 2) error->all(FLERR,"Illegal variable command: expected 2 arguments but found {}", narg);
     int ivar = find(arg[0]);
     if (ivar >= 0) {
       if (style[ivar] != TIMER)
@@ -531,7 +534,7 @@ void Variable::set(int narg, char **arg)
   // dvalue = numeric initialization from 2nd arg, reset by internal_set()
 
   } else if (strcmp(arg[1],"internal") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     int ivar = find(arg[0]);
     if (ivar >= 0) {
       if (style[ivar] != INTERNAL)
@@ -551,7 +554,7 @@ void Variable::set(int narg, char **arg)
 
   // unrecognized variable style
 
-  } else error->all(FLERR,"Illegal variable command");
+  } else error->all(FLERR,"Unknown variable keyword: {}", arg[1]);
 
   // set name of variable, if not replacing one flagged with replaceflag
   // name must be all alphanumeric chars or underscores