diff --git a/cmd/modhex.go b/cmd/modhex.go
new file mode 100644
index 0000000..20ec8b8
--- /dev/null
+++ b/cmd/modhex.go
@@ -0,0 +1,81 @@
+package main
+
+import (
+	"encoding/hex"
+	"flag"
+	"fmt"
+	"os"
+	"strings"
+
+	"git.trashheap.io/blinkthethings/modhex"
+)
+
+func main() {
+	// configure command line flags
+	var decode, hexdata bool
+	flag.BoolVar(&decode, "d", false, "decode data (the default is to encode).")
+	flag.BoolVar(&hexdata, "x", false, "Use hex encoding for non-modhex data.")
+	flag.Usage = func() {
+		fmt.Println("modhex - encode/decode data using modhex encoding.")
+		fmt.Println()
+		fmt.Println("Usage:\n\n  modex [-d] [-x] <data>")
+		fmt.Println()
+		fmt.Println("  Convert input DATA as specified and print output to STDOUT.")
+		fmt.Println()
+		fmt.Printf("Flags:\n\n")
+		flag.PrintDefaults()
+		fmt.Println()
+	}
+	flag.Parse()
+
+	if decode {
+		// decode was selected
+
+		// read the modhex string from the command line
+		src := []byte(strings.Join(flag.Args(), " "))
+
+		// create a buffer to hold the decoded data
+		dst := make([]byte, modhex.DecodedLen(len(src)))
+
+		// decode the input
+		_, err := modhex.Decode(dst, src)
+		if err != nil {
+			// report the error to the user
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(-1)
+		}
+
+		// should the output be a hex string?
+		if hexdata {
+			// print out the decoded data as a hex string
+			fmt.Println(hex.EncodeToString(src))
+		} else {
+			// print out the decoded bytes stdout
+			os.Stdout.Write(dst)
+		}
+	} else {
+		// encode was selected
+
+		// read the input data
+		var src []byte
+		if hexdata {
+			// read the input as a hex string
+			var err error
+			src, err = hex.DecodeString(flag.Arg(0))
+			if err != nil {
+				// report the hex decode error and exit
+				fmt.Fprintf(os.Stderr, "modhex: %s\n", err)
+				os.Exit(-1)
+			}
+		} else {
+			// read the input as bytes
+			src = []byte(strings.Join(flag.Args(), ""))
+		}
+
+		// encode the input
+		s := modhex.EncodeToString(src)
+
+		// print out the modhex encoded string
+		fmt.Println(s)
+	}
+}