There are many HTTP status codes for different situations, but most writers only know two which are both Client Error codes: 403 Forbidden and 404 Not Found. They are often referenced as a joke or Genius Bonus, though the latter applies especially if writers do use a different code than the aforementioned 403 and 404. They can also be used as showing something being changed or refused for 403 and destroyed or unavailable for 404.
- Vainqueur the Dragon: From "Landfall":
ERROR 404: Soul not found!
- Kamen Rider Zero-One: The theme song, "REALxEYEZ" , refers to the "404 Not Found" error. The extended version of the song from the OST also mentions the lesser known 408 (Request) Timeout error.
- Deus Ex: Human Revolution, at the Picus Office, Jensen tries to track Eliza Cassan (whom, unknown to him, is an AI). The first room he's lead to check is room 404. Unsurprisingly, he fails to actually find her there (finding only a hologram of her).
- Devil Survivor 2 ends its Game Over message with 403 Forbidden. The message often appears when a website's code is being rewritten. In the context of the game, the world is being altered. Its Updated Re-release Record Breaker goes for 404 Not Found instead, to signify the world being destroyed.
- Epic Battle Fantasy 5: Using a Limit Break that shows Earth in its animation after the Devourer's deleted the world will instead show the animation with Earth replaced with a black circle with a red outline and "ERROR 404: NOT FOUND" in red.
- Girls Frontline: One of the more prominent squads featured in the game's story is called "404", presumably named for their status as a small, clandestine, independent black ops squad who wipes the memory of their clients after every mission. Even the main characters are no exception to this treatment.
- The Impossible Quiz Book: After wiping the Impossible Quiz from history and ending the game, you're shown the message "Error 404 "The Impossible Quiz.swf" could not be found".
- Skullgirls has plenty of lines for combo ratings. 403 has "Forbidden" and 404 has "Not Found".
- Super Paper Mario: One of the lines Fracktail says after being corrupted is "404 computer hamsters not found".
- Science Girls!: For both 403 and 404:
- Classroom 403 has a blackboard that says: Entrance Forbidden - This means you".
- If classroom 404 is entered while Missy is in the party, as the Science Club member who's focus is Computers, she says:
404 monster not found!
- BoxxyQuest: The Shifted Spires: The 404 Orb, a reference to the "404 Not Found" Error Code... broke the Internet when tossed into its core, instead of destroying it as its user intended.