--- /dev/null
+1to2 naively converts source code files from NAN 1 to NAN 2. There will be erroneous conversions,
+false positives and missed opportunities. The input files are rewritten in place. Make sure that
+you have backups. You will have to manually review the changes afterwards and do some touchups.
+
+```sh
+$ tools/1to2.js
+
+ Usage: 1to2 [options] <file ...>
+
+ Options:
+
+ -h, --help output usage information
+ -V, --version output the version number
+```