diff --git a/eeshow/Makefile b/eeshow/Makefile
index 4823180..bf657a6 100644
--- a/eeshow/Makefile
+++ b/eeshow/Makefile
@@ -16,7 +16,7 @@ NAME = eeshow
 OBJS = main.o version.o \
        kicad/sch-parse.o kicad/sch-render.o kicad/lib-parse.o \
        kicad/lib-render.o kicad/dwg.o kicad/delta.o kicad/sexpr.o \
-       kicad/pl-parse.o kicad/pl-render.o \
+       kicad/pl-parse.o kicad/pl-render.o kicad/ext.o \
        gui/gui.o gui/over.o gui/style.o gui/aoi.o gui/fmt-pango.o gui/input.o \
        gui/progress.o gui/glabel.o gui/sheet.o gui/history.o gui/render.o \
        gui/help.o gui/icons.o \
diff --git a/eeshow/kicad/ext.c b/eeshow/kicad/ext.c
new file mode 100644
index 0000000..961f231
--- /dev/null
+++ b/eeshow/kicad/ext.c
@@ -0,0 +1,87 @@
+/*
+ * kicad/ext.c - Identify file by their extension
+ *
+ * Written 2016 by Werner Almesberger
+ * Copyright 2016 by Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "misc/diag.h"
+#include "kicad/ext.h"
+
+
+enum ext identify(const char *path)
+{
+	const char *dot, *slash;
+
+	dot = strrchr(path, '.');
+	if (!dot)
+		return ext_unknown;
+	slash = strchr(dot + 1, '/');
+	if (slash)
+		return ext_unknown;
+
+	if (!strcmp(dot, ".pro"))
+		return ext_project;
+	if (!strcmp(dot, ".sch"))
+		return ext_sch;
+	if (!strcmp(dot, ".lib"))
+		return ext_lib;
+	if (!strcmp(dot, ".kicad_wks"))
+		return ext_pl;
+
+	return ext_unknown;
+}
+
+
+void classify_files(struct file_names *fn, char *const *args,
+    unsigned n_args)
+{
+	unsigned i;
+
+	fn->pro = fn->sch = fn->pl = NULL;
+	fn->libs = NULL;
+	fn->n_libs = 0;
+
+	for (i = 0; i != n_args; i++) {
+		switch (identify(args[i])) {
+		case ext_unknown:
+			fatal("%s: unknown file type", args[i]);
+		case ext_project:
+			if (fn->pro)
+				fatal("%s: there can only be one project",
+				    args[i]);
+			fn->pro = args[i];
+			break;
+		case ext_sch:
+			if (fn->sch)
+				fatal("%s: there can only be one top sheet",
+				    args[i]);
+			fn->sch = args[i];
+			break;
+		case ext_lib:
+			fn->n_libs++;
+			fn->libs = realloc(fn->libs,
+			    fn->n_libs * sizeof(const char *));
+			if (!fn->libs)
+				diag_pfatal("realloc");
+			fn->libs[fn->n_libs - 1] = args[i];
+			break;
+		case ext_pl:
+			if (fn->pl)
+				fatal("%s: there can only be one page layout",
+				    args[i]);
+			fn->pl = args[i];
+			break;
+		default:
+			abort();
+		}
+	}
+}
diff --git a/eeshow/kicad/ext.h b/eeshow/kicad/ext.h
new file mode 100644
index 0000000..0986edd
--- /dev/null
+++ b/eeshow/kicad/ext.h
@@ -0,0 +1,39 @@
+/*
+ * kicad/ext.h - Identify files by their extension
+ *
+ * Written 2016 by Werner Almesberger
+ * Copyright 2016 by Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#ifndef KICAD_EXT_H
+#define	KICAD_EXT_H
+
+enum ext {
+	ext_unknown,
+	ext_project,
+	ext_sch,
+	ext_lib,
+	ext_pl,		/* .kicad_wks, work sheet */
+};
+
+
+struct file_names {
+	const char *pro;	/* just one allowed, may be NULL */
+	const char *sch;	/* just one allowed, may be NULL */
+	const char *pl;		/* just one allowed, may be NULL */
+	const char **libs;
+	unsigned n_libs;
+};
+
+
+enum ext identify(const char *path);
+void classify_files(struct file_names *fn, char *const *args, 
+    unsigned n_args);
+
+#endif /* !KICAD_EXT_H */