diff --git a/admin.php b/admin.php
new file mode 100644
index 0000000..db481ba
--- /dev/null
+++ b/admin.php
@@ -0,0 +1,142 @@
+<?php
+
+function init_postode_admin()
+{
+    add_action("admin_menu", "local_postcodes_admin_menu", 99);
+    add_action("admin_head", "local_postcodes_admin_css");
+    add_action("admin_init", "local_postcodes_register_settings"); // Correct
+}
+
+function local_postcodes_admin_menu()
+{
+    add_submenu_page(
+        "woocommerce", // Parent menu slug
+        "Lokale Postcodes", // Page title
+        "Lokale Postcodes", // Menu title
+        "manage_options", // Capability
+        "local-postcodes", // Menu slug
+        "generate_admin_page", // Callback function
+        "dashicons-buddicons-pm", // Optional icon URL or dashicon
+    );
+}
+
+function local_postcodes_register_settings()
+{
+    register_setting(
+        "my_plugin_options",
+        "local_postcodes_values",
+        "local_postcodes_input_validate",
+    );
+}
+
+function generate_admin_page()
+{
+    ?>
+    <div class="wrap">
+        <h1><span class="dashicons dashicons-admin-home"></span> Lokale Postcodereeksen</h1>
+        <?php settings_errors("local_postcodes_error_messages"); ?>
+        <div class="info">
+        <p class="info">Vul hier de lokale postcodereeksen in.</p>
+        <ul>
+            <li>Het formaat voor een reeks is #### | #### (voorbeeld: 5000 | 5199).</li>
+            <li>Plaats één reeks op één regel.</li>
+            <li>Om een reeks te verwijderen. Wis de reeks en sla vervolgens de wijzigen op.</li>
+        </ul>
+        </div>
+        <form id="postcodes_form" method="post" action="options.php">
+            <?php
+            settings_fields("my_plugin_options");
+            do_settings_sections("my_plugin_options");
+            ?>
+            <textarea id="local_postcodes_values" name="local_postcodes_values"><?php echo esc_textarea(
+                get_option("local_postcodes_values"),
+            ); ?></textarea>
+            <?php submit_button(); ?>
+        </form>
+    </div>
+    <?php
+}
+
+function local_postcodes_admin_css()
+{
+    ?>
+    <style>
+        h1 .dashicons{
+            font-size: 25px;
+
+        }
+
+        .info {
+            font-size: 1.1rem;
+            max-width: 60ch;
+
+            ul {
+                list-style: square inside;
+            }
+        }
+
+        #postcodes_form {
+            display: flex;
+            flex-direction: column;
+            max-width: 60ch;
+            align-items: flex-end;
+            font-size: 1.1rem;
+
+            #local_postcodes_values{
+                width: 100% !important;
+                height: 50vh !important;
+                font-size: 1.1rem;
+            }
+
+
+            .submit{
+                margin-top: .2rem;
+            }
+        }
+    </style>';
+    <?php
+}
+
+function local_postcodes_input_validate($input)
+{
+    $valid_input = "";
+    $lines = preg_split("/\R/", $input, -1, PREG_SPLIT_NO_EMPTY);
+    $pattern = '/^\d{4}\s*\|\s*\d{4}$/';
+    $pc_arr = [];
+
+    foreach ($lines as $line) {
+        $line = trim($line);
+        if (preg_match($pattern, $line)) {
+            $parts = explode("|", $line);
+            $first = (int) $parts[0];
+            $second = (int) $parts[1];
+
+            if ($first <= $second) {
+                $pc_arr[] = [$first, $second];
+            } else {
+                $pc_arr[] = [$second, $first];
+            }
+        } else {
+            add_settings_error(
+                "local_postcodes_error_messages",
+                "invalid_postcode_" . md5($line),
+                'Ongeldige regel: "' .
+                    esc_html($line) .
+                    '". Gebruik het formaat #### | ####.(bijvoorbeeld: 5000 | 5199)',
+                "error",
+            );
+        }
+    }
+
+    // Sorteer de VOLLEDIGE array NA de foreach-lus
+    usort($pc_arr, function ($a, $b) {
+        return $a[0] <=> $b[0];
+    });
+
+    // Bouw $valid_input op uit de gesorteerde $pc_arr
+    foreach ($pc_arr as $range) {
+        $valid_input .= $range[0] . " | " . $range[1] . "\n";
+    }
+
+    return $valid_input;
+}