What is whereismyfamiliar?

WITF, short for What Is The Familiar, is a rulebook meant to turn Claude into the game master for a short roleplaying story. It is not an app or a piece of software you install. Instead you paste the contents of a single markdown file into Claude's custom instructions, and Claude then runs the game for you inside a normal chat. The game starts with one simple question about how much time you have, and after that there are no menus or lists of choices. You type what your character does in your own words, and Claude quietly keeps track of the choices you make as the story unfolds. When the story reaches its end, Claude builds an original three dimensional creature, described as a companion, based on how you actually played, and hands it to you as a file you can keep. No two players who start the same way will end up with the same creature, since the creature reflects the specific choices each person made. To play, a user opens Claude, starts a Project or a fresh chat, pastes the rulebook file into the Project's custom instructions, and simply says something like begin to start. Because the ending step involves generating and delivering a file, the README notes that this requires a Claude plan that includes code execution and file creation features. The author explains that the underlying design goal is to keep the experience feeling like a story rather than a system being operated, so the rules deliberately hide dice rolls, scores, and other mechanics until after the story is finished. The rulebook itself contains a couple of sections that lay out this design philosophy in full for anyone curious. The project is offered free for people to use, adapt, and build on, with a license file included in the repository for the exact terms, and the author asks that anyone extending it keep the mechanics hidden from the player. The README notes that the project is not affiliated with or endorsed by Anthropic, it is simply built to run on top of Claude.