Fail Fast

Use this skill to make a codebase deterministic by finding and removing hidden fallback behavior that should be an explicit contract, validation error, migration, or test fixture.

State at the start that you are using the fail-fast skill.

Core Rule

Prefer one canonical path and one explicit failure mode.

A fallback is allowed only when it is a real product requirement, a documented migration window, or an intentional local-test fixture. Everything else should become a validation error, required input, explicit branch, deleted compatibility layer, or typed configuration contract.

Workflow

Identify the target repo and its package manager.
Run the scanner before editing (path is relative to this skill's directory):