diff --git a/.gitignore b/.gitignore
index c18dd8d..7a60b85 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 __pycache__/
+*.pyc
diff --git a/fhex/__main__.py b/fhex/__main__.py
index 98391df..c558885 100644
--- a/fhex/__main__.py
+++ b/fhex/__main__.py
@@ -1,11 +1,58 @@
 import argparse
+import sys
 
+import fhex.parse
 
 def main():
-    parser = argparse.ArgumentParser()
+    parser = argparse.ArgumentParser(
+        description="Convert hex strings to and from human-readable strings.")
+    parser.add_argument("-f", "--format", default="APNF")
+    parser.add_argument("-x", "--hex", nargs="?", const="-",
+        help="Hex code to translate to friendly string. If no value is" +
+        " specified, read hex from stdin.")
+    parser.add_argument("-s", "--string", nargs="?", const="-",
+        help="Friendly string to translate to hex. If no value is specified," +
+        " read string from stdin.")
+    parser.add_argument("--titlecase", action="store_true",
+        help="Titlecase friendly string output.")
+    parser.add_argument("--hyphenate", action="store_true",
+        help="Hyphenate friendly string output.")
+    parser.add_argument("-v", "--verbose", action="store_true")
+
     args = parser.parse_args()
 
-    print("Hello, world!")
+    if args.verbose:
+        print("friendly-hex", file=sys.stderr)
+        print("  --format =", args.format, file=sys.stderr)
+        print("  --hex =", args.hex, file=sys.stderr)
+        print("  --string =", args.string, file=sys.stderr)
+        print("  --titlecase =", args.titlecase, file=sys.stderr)
+        print("  --hyphenate =", args.hyphenate, file=sys.stderr)
+        print("  --verbose =", args.verbose, file=sys.stderr)
+        print(file=sys.stderr)
+
+    if args.hex is None and args.string is None:
+        parser.error("One of --hex or --string is required.")
+
+    if args.hex is not None and args.string is None:
+        # Convert hex to friendly string
+        if args.hex == "-":
+            args.hex = sys.stdin.readline().strip()
+            if args.verbose:
+                print(f'Read "{args.hex}" from stdin', file=sys.stderr)
+
+        words = fhex.parse.hex_to_friendly(args.hex, args.format)
+        if args.titlecase:
+            words = [word.title() for word in words]
+
+        joiner = "-" if args.hyphenate else " "
+        joined = joiner.join(words)
+
+        print(joined)
+
+    if args.hex is None and args.string is not None:
+        # Convert friendly string to hex
+        raise NotImplementedError()
 
 
 if __name__ == "__main__":
diff --git a/fhex/parse.py b/fhex/parse.py
new file mode 100644
index 0000000..1914af2
--- /dev/null
+++ b/fhex/parse.py
@@ -0,0 +1,49 @@
+import math
+
+from fhex.words import ADJECTIVE, PARTICIPLE, NOUN, PHONETIC
+
+
+DEFAULT_FORMAT_DEF = {
+    "A": ADJECTIVE,
+    "P": PARTICIPLE,
+    "N": NOUN,
+    "F": PHONETIC,
+}
+
+
+def hex_to_friendly(hex_str, format_str):
+    hex_i, fmt_i = 0, 0
+    words = []
+    fmt_def = DEFAULT_FORMAT_DEF
+    while hex_i < len(hex_str):
+        if fmt_i >= len(format_str):
+            raise Exception("Format string is too short")
+        fmt_code = format_str[fmt_i]
+
+        if fmt_code not in fmt_def:
+            raise Exception(f"Unrecognized format code: {fmt_code}")
+        fmt_list = fmt_def[fmt_code]
+
+        fmt_len = math.log(len(fmt_list), 16)
+        if fmt_len % 1 != 0:
+            raise Exception(
+                f"Word list for {fmt_code} must be a power of 16" +
+                " (length: {len(fmt_list)})")
+        fmt_len = int(fmt_len)
+
+        if hex_i + fmt_len > len(hex_str):
+            raise Exception(f"Not enough hex characters for format code {fmt_code}")
+
+        hex_part = hex_str[hex_i:hex_i + fmt_len]
+        fmt_list_i = int(hex_part, 16)
+        word = fmt_list[fmt_list_i]
+        words.append(word)
+
+        hex_i += fmt_len
+        fmt_i += 1
+
+    if fmt_i != len(format_str):
+        raise Exception("Format string is too long")
+
+    return words
+