Secret code

"I see, I see. A flying saucer has arrived for you. Here you go. Thank you much."

- Tom Nook

Secret codes, also known as passwords or simply codes, are passwords used in, and  to give and receive in-game items. The way codes work in each game varies.

Formatting and input
In Japanese games, codes consist of 22 characters in two rows of 11. In, codes consist of 28 characters displayed as two rows of 14 characters each. Valid code characters include all uppercase and lowercase letters of the English alphabet, the numbers 0, 2, 3, 4, 5, 6, 7, 8, 9, the ampersand (&), the at sign (@), the pound (#), and the percent sign (%). The number zero and uppercase "o" are interchangeable. When generated by Tom Nook, a capital "i" can be distinguished from a lowercase "L" by the serif drawn at both the top and bottom of its stem. Note also that the number "1" is never generated in a secret code.

Passwords can either be input by sending them in a letter to a villager (in, and ) or telling them to Tom Nook (in  and  only}}. A password letter must be formatted in three lines: in Japanese games, the first line is the word あいことば (meaning secret password) and the second and third lines are 11 characters each; in , the first line must be the special key symbol, and the second and third lines are 14 characters each. The player will receive their item in a letter from a different character depending on the type of password two days later. While these are unlimited, Tom Nook will only distribute three items via password per game load. To redeem more items, the player must save and quit and then reload the game.

Types of codes
There are several types of secret codes the games can read.

, and  each makes use of a variety of code types, each of which serves a different purpose and has a different origin. All code types follow the same description as outlined in the introduction and thus appear very similar to the untrained eye. They are listed below using the games' internal names and colloquial names.

In, the original three types of codes were:


 * Famicom/"NES codes": These codes were used to distribute NES games on Nintendo's website. They are generated using input of the player's name and town name, and are sent by mail to random villagers. These codes cannot be used for the "Forbidden Four" NES games,, Super Mario Bros, , and Legend of Zelda.
 * ,, , , and were exclusively released on the official Animal Crossing website using NES contest codes and can only be obtained through this manner; universal codes cannot be generated for these titles. As the game's official site is no longer online, these five games are now solely available via third-party code generators capable of creating this specialized code type.


 * NPC/"Villager codes": These codes were also used on Nintendo's website to distribute other items, also requiring the player and town name and sent by mail. They are named such because they were sent to villagers who sent back a gift.


 * Card E/"e-Reader card codes": These codes are written on the back of most and  e-Reader cards. As such, they will work for any town/player, and are sent by mail. Each villager code corresponds to a certain item that is different from the one received from scanning the card. If the letter is sent to the character on the card, there is a 60% chance of a common NES game and a 40% chance of the particular item. If the letter is sent to the specific villager on the card, the particular item is guaranteed. However, after the code is used, it will give a random item instead.
 * In, due to prioritization and accessibility of scanning e-Reader cards for gifts, using a code from a card in a letter will only give one of three items obtainable only in this way: the , the , or.

added three more types of codes:


 * Magazine/"contest" codes: These codes were usually included in magazines such as Nintendo Power and sometimes the Nintendo website, and as such work for any town and player. They are redeemed by telling them to Tom Nook. These codes include a "hit rate" value that could be 0%, 30%, 60% or 100%. However, if the player loses they can simply try again. In practice, all official codes shared in magazines and websites had a 100% guaranteed hit rate. Due to this and their availability to any player, these and externally-generated Card E and Card E Mini codes are sometimes called "universal codes".


 * User/"Player-to-player" codes: These codes can be generated specifically for another player by telling Tom Nook their player and town name, and are redeemed with him as well. They intend to mimic the experience of a personalized delivery service. Nook will only generate passwords for items that are orderable from the catalog (plus Mushrooms and Candy).
 * Prior to the discovery of "universal" codes which work for any player regardless of name/town combination, fans created a group named Project Hyrule, whose sole goal was to amass a list of player-to-player codes for every item in the game. To take advantage of such a list, each member used the credentials Link in Hyrule when creating their town. After the advent and proliferation of code generators the group eventually became redundant, however their dedicated cryptologists did manage to generate many universal codes, which when redeemed at Nook's provide the player with a gift from "Project Hyrule."


 * Card E Mini: These codes are received upon completing certain minigames on the Nintendo e-Reader, and are given to Tom Nook. They are another type of "universal" code that will work for any player.

Finally, added two more code types:


 * New NPC: The same as the NPC/"villager codes" above, sent by mail, but specific to e+.


 * Monument: Codes generated based on player and town names on Nintendo's now-defunct Object Delivery Service website, which, when given to Nook, allow for certain Objects in the player's town.

Mario Theme codes
Some contest codes were used by Nintendo to distribute the Mario Theme, with codes for individual pieces listed in various issues of Nintendo Power magazine and on the official website. The Nintendo Bench code was distributed through Tips & Tricks magazine.

Cross-compatibility
The secret codes used in Animal Crossing are not compatible with any Japanese titles, nor can English code generators create codes that will work for Japanese games. Japanese universal codes do exist, however, and Japanese code generators may have been developed independently of their English counterparts, however their current status is unknown.

Code messages
Different code types will result in different messages from Nook. These messages can be used to determine a code's type as well as to diagnose potential issues when a code is not working.

Wrong password: This message is received after entering a player-to-player code that has a few typographical errors, but that is otherwise correct and can be redeemed by the player.
 * "Now that's odd... I think there's something the matter with your password. Do you want to tell it to me again?"

Someone else's password: This message is received after entering a player-to-player code that was not sent to the player's specific character and/or town name.
 * "Oh?! What's this? You can't use that password, [player name]! Don't try to trick me by using someone else's password! Do you have a password of your own that you'd like to try?"

Send to animal: This message is received after telling Nook a villager code. This code type can only be redeemed by sending a letter to a villager in town. When mailing a villager code, make sure the key symbol appears by itself on the first line, the first line of code is placed on the second line, and second line of code sits on the third line of the letter. The villager will respond in a few days. If there is not a present attached to the letter then the code was typed incorrectly or is invalid.
 * "Eh? I'm sorry, but that password isn't valid here. Try sending it to one of the animals living in [player's town]."

Contest winner: There are two alternate dialogues for contest codes, one which mentions the sender's name and one which mentions the contest's name.
 * "I see, I see. A [item] has arrived for you from [sender's name]. Please take your present. Thank you much."
 * "I see, I see. This [item] is the prize for winning [contest name]. Congratulations! Thank you much."

Contest loser: This message is received after entering a losing contest code. Note that if the player attempts to reenter the code they may eventually 'win' the item.
 * "I see, I see... ...Now, this IS regrettable! Based on the notification I've received directly from [name]... it seems you are NOT a winner. But thank you much for trying!"