diff --git a/libc/include/err.h b/libc/include/err.h
index a64d01d..e91dac9 100644
--- a/libc/include/err.h
+++ b/libc/include/err.h
@@ -1,6 +1,3 @@
-/*	$OpenBSD: err.h,v 1.10 2006/01/06 18:53:04 millert Exp $	*/
-/*	$NetBSD: err.h,v 1.11 1994/10/26 00:55:52 cgd Exp $	*/
-
 /*-
  * Copyright (c) 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -32,8 +29,12 @@
  *	@(#)err.h	8.1 (Berkeley) 6/2/93
  */
 
-#ifndef _ERR_H_
-#define _ERR_H_
+#pragma once
+
+/**
+ * @file err.h
+ * @brief BSD error reporting functions. See `<error.h>` for the GNU equivalent.
+ */
 
 #include <stdarg.h>
 #include <sys/cdefs.h>
@@ -41,15 +42,76 @@
 
 __BEGIN_DECLS
 
+/**
+ * [err(3)](http://man7.org/linux/man-pages/man3/err.3.html) outputs the program name,
+ * the printf()-like formatted message, and the result of strerror() if `errno` is non-zero.
+ *
+ * Calls exit() with `__status`.
+ *
+ * New code should consider error() in `<error.h>`.
+ */
 __noreturn void err(int __status, const char* __fmt, ...) __printflike(2, 3);
+
+/**
+ * [verr(3)](http://man7.org/linux/man-pages/man3/verr.3.html) outputs the program name,
+ * the vprintf()-like formatted message, and the result of strerror() if `errno` is non-zero.
+ *
+ * Calls exit() with `__status`.
+ *
+ * New code should consider error() in `<error.h>`.
+ */
 __noreturn void verr(int __status, const char* __fmt, va_list __args) __printflike(2, 0);
+
+/**
+ * [errx(3)](http://man7.org/linux/man-pages/man3/errx.3.html) outputs the program name, and
+ * the printf()-like formatted message.
+ *
+ * Calls exit() with `__status`.
+ *
+ * New code should consider error() in `<error.h>`.
+ */
 __noreturn void errx(int __status, const char* __fmt, ...) __printflike(2, 3);
+
+/**
+ * [verrx(3)](http://man7.org/linux/man-pages/man3/err.3.html) outputs the program name, and
+ * the vprintf()-like formatted message.
+ *
+ * Calls exit() with `__status`.
+ *
+ * New code should consider error() in `<error.h>`.
+ */
 __noreturn void verrx(int __status, const char* __fmt, va_list __args) __printflike(2, 0);
+
+/**
+ * [warn(3)](http://man7.org/linux/man-pages/man3/warn.3.html) outputs the program name,
+ * the printf()-like formatted message, and the result of strerror() if `errno` is non-zero.
+ *
+ * New code should consider error() in `<error.h>`.
+ */
 void warn(const char* __fmt, ...) __printflike(1, 2);
+
+/**
+ * [vwarn(3)](http://man7.org/linux/man-pages/man3/vwarn.3.html) outputs the program name,
+ * the vprintf()-like formatted message, and the result of strerror() if `errno` is non-zero.
+ *
+ * New code should consider error() in `<error.h>`.
+ */
 void vwarn(const char* __fmt, va_list __args) __printflike(1, 0);
+
+/**
+ * [warnx(3)](http://man7.org/linux/man-pages/man3/warnx.3.html) outputs the program name, and
+ * the printf()-like formatted message.
+ *
+ * New code should consider error() in `<error.h>`.
+ */
 void warnx(const char* __fmt, ...) __printflike(1, 2);
+
+/**
+ * [vwarnx(3)](http://man7.org/linux/man-pages/man3/warn.3.html) outputs the program name, and
+ * the vprintf()-like formatted message.
+ *
+ * New code should consider error() in `<error.h>`.
+ */
 void vwarnx(const char* __fmt, va_list __args) __printflike(1, 0);
 
 __END_DECLS
-
-#endif /* !_ERR_H_ */