diff --git a/src/hwylterm/hwylcli.nim b/src/hwylterm/hwylcli.nim
index c40fba6..da84632 100644
--- a/src/hwylterm/hwylcli.nim
+++ b/src/hwylterm/hwylcli.nim
@@ -514,6 +514,34 @@ func pasrseCliAlias(cfg: var CliCfg, node: NimNode) =
       cfg.alias.incl s
     else: bad(n, "alias")
 
+func err(c: CliCfg, msg: string) =
+  ## quit with error while generating cli
+  error "failed to generate " & c.name & " hwylcli: \n" & msg
+
+func check(c: CliCfg) =
+  ## verify the cli is valid
+  var
+    short: Table[char, CliFlag]
+    long: Table[string, CliFlag]
+
+  for f in c.flags:
+    if f.short != '\x00':
+      if f.short in short:
+        let conflict = short[f.short]
+        c.err "conflicting short flags for: " & f.name & " and " & conflict.name
+        # hwylCliImplError c, (
+        #   "conflicting short flags for: " & f.name & " and " & conflict.name
+        # )
+
+      else:
+        short[f.short] = f
+
+    if f.long in long:
+      let conflict = long[f.long]
+      c.err "conflicting long flags for: " & f.name & " and " & conflict.name
+    else:
+      long[f.long] = f
+
 func propagate(c: var CliCfg) =
   for child in c.subcommands.mitems:
     # push the preSub to the lowest subcommand
@@ -524,7 +552,9 @@ func propagate(c: var CliCfg) =
       child.pre = c.preSub
       child.post = c.postSub
     child.inheritFrom(c)
-    propagate(child)
+    propagate child
+    check child
+
 
 func parseCliHelp(c: var CliCfg, node: NimNode) =
   ## some possible DSL inputs:
@@ -662,7 +692,11 @@ func subCmdsArray(cfg: CliCfg): NimNode =
     result.add quote do:
       (`cmd`, `aliases`, `desc`)
 
-proc hwylCliError*(msg: string | BbString) =
+# is this one necessary?
+proc hwylCliError*(msg: BbString) =
+  quit $(bb("error ", "red") & msg)
+
+proc hwylCliError*(msg: string) =
   quit $(bb("error ", "red") & bb(msg))
 
 func defaultUsage(cfg: CliCfg): NimNode =
diff --git a/tests/example.nim b/tests/example.nim
index f5456dd..0d6dfcb 100644
--- a/tests/example.nim
+++ b/tests/example.nim
@@ -12,8 +12,8 @@ hwylCli:
   flags:
     [global]
     color:
-        T Color
-        ? "a color (red, green, blue)"
+      T Color
+      ? "a color (red, green, blue)"
     yes:
       T bool
       ? "set flag to yes"
diff --git a/todo.md b/todo.md
index 96e272c..b8f44a7 100644
--- a/todo.md
+++ b/todo.md
@@ -22,7 +22,7 @@
 - [x] add support to either (lengthen commands) or provide an alias for a subcommand
 - [x] add command aliases to hwylcli help with switch
 - [x] don't recreate "global"" variables in var section
-- [ ] add flag overlap check before case statement generation (use `postParse` proc)
+- [x] add flag overlap check before case statement generation (use `postParse` proc)
 - [x] add key-value flag support -> `--setting:a:off`
 - [x] add defaultFlagType CliCfg setting
 - [x] add node to flagDef to override builtin `parse(p, varName)`