diff --git a/includes/_internal.h b/includes/_internal.h
new file mode 100644
index 0000000..407417e
--- /dev/null
+++ b/includes/_internal.h
@@ -0,0 +1,48 @@
+/* ************************************************************************** */
+/*                                                                            */
+/*                                                        :::      ::::::::   */
+/*   _internal.h                                        :+:      :+:    :+:   */
+/*                                                    +:+ +:+         +:+     */
+/*   By: rparodi <rparodi@student.42.fr>            +#+  +:+       +#+        */
+/*                                                +#+#+#+#+#+   +#+           */
+/*   Created: 2025/09/19 17:15:50 by rparodi           #+#    #+#             */
+/*   Updated: 2025/09/19 17:25:25 by rparodi          ###   ########.fr       */
+/*                                                                            */
+/* ************************************************************************** */
+
+#ifndef _INTERNAL_H
+# define _INTERNAL_H
+
+# include <stdarg.h>
+# include <stdint.h>
+# include <stddef.h>
+
+typedef int	(*t_func)(va_list, int fd);
+
+typedef struct s_format
+{
+	char	character;
+	t_func	function;
+}			t_format;
+
+size_t	ft_strlen(const char *str);
+
+char	*itoa_base(uint64_t nbr, char *base);
+
+int		flag_c(va_list args, int fd);
+
+int		flag_i(va_list args, int fd);
+
+int		flag_p(va_list args, int fd);
+
+int		flag_percent(va_list args, int fd);
+
+int		flag_s(va_list args, int fd);
+
+int		flag_u(va_list args, int fd);
+
+int		flag_x(va_list args, int fd);
+
+int		flag_x_maj(va_list args, int fd);
+
+#endif
diff --git a/sources/ft_printf.c b/sources/ft_printf.c
index 3ffd37c..1c56d56 100644
--- a/sources/ft_printf.c
+++ b/sources/ft_printf.c
@@ -6,11 +6,11 @@
 /*   By: rparodi <rparodi@student.42.fr>            +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2025/09/17 17:44:34 by rparodi           #+#    #+#             */
-/*   Updated: 2025/09/19 15:35:38 by rparodi          ###   ########.fr       */
+/*   Updated: 2025/09/19 17:17:12 by rparodi          ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
-#include "ft_printf.h"
+#include "_internal.h"
 #include <stdarg.h>
 #include <stddef.h>
 #include <stdio.h>
diff --git a/sources/print_char.c b/sources/print_char.c
index b559e77..4462656 100644
--- a/sources/print_char.c
+++ b/sources/print_char.c
@@ -10,7 +10,7 @@
 /*                                                                            */
 /* ************************************************************************** */
 
-#include "ft_printf.h"
+#include "_internal.h"
 #include <stdarg.h>
 #include <stddef.h>
 #include <stdio.h>
diff --git a/sources/print_number.c b/sources/print_number.c
index a1a19a5..e3659ab 100644
--- a/sources/print_number.c
+++ b/sources/print_number.c
@@ -6,11 +6,11 @@
 /*   By: rparodi <rparodi@student.42.fr>            +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2025/09/18 15:00:27 by rparodi           #+#    #+#             */
-/*   Updated: 2025/09/19 16:06:27 by rparodi          ###   ########.fr       */
+/*   Updated: 2025/09/19 17:19:45 by rparodi          ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
-#include "ft_printf.h"
+#include "_internal.h"
 #include <limits.h>
 #include <stddef.h>
 #include <stdlib.h>