goatstarter/goat-fable

Goat Fable is a behavior pack for Claude Opus 4.8 that tries to give it some of the working habits of Fable 5, a different Claude model the author considers stronger at agentic coding. The README, written in Turkish with an English section, explains that a prompt pack cannot add raw intelligence to a model, but it can shape behavior, and a lot of day-to-day coding performance comes down to behavior: whether the model verifies its own claims of being done, avoids papering over bugs instead of fixing their root cause, and does not silently drop parts of a multi-step request. The project is organized in layers. A small core file of about 200 lines is always loaded and defines around twelve behavior rules. On top of that sit four Claude Code skills that trigger automatically in specific situations, such as planning before complex work, debugging after repeated failed fixes, or reviewing a diff before calling a task finished. Deeper guides on topics like debugging, verification, and long multi-step tasks are loaded only when needed. A hook enforces a deterministic check: if changes were made but no tests were run, the session is stopped once before it can exit. A separate verifier agent reviews completed work with a fresh, independent context rather than relying on the same agent grading its own output. The README includes a comparison table showing example behavior differences between plain Opus 4.8 and Opus 4.8 running with Goat Fable, covering situations like reporting whether a task is truly finished, handling a difficult bug, and reviewing code for issues. It states the target list of behaviors is based on Anthropic's own published documentation comparing Fable 5 and Opus 4.8. Installation is a git clone followed by running an install script pointed at your project directory, then starting a Claude Code session and selecting the Opus 4.8 model with a high effort setting. The repository also includes an eval folder with eight test tasks and a scoring rubric so you can measure the pack's effect on your own repository, and API-friendly system prompts for using the same behavior rules outside Claude Code. The project is MIT licensed.