Use when adding, reviewing, or changing environment variables, .env files, process.env access, deployment secrets, runtime configuration, feature flags, CLI flags, command arguments, boolean toggles, or setup docs. Encourages keeping env vars for configuration that genuinely varies across environments, and using CLI flags, arguments, config files, code-level constants, or application toggles for ordinary behavior choices.
Use after making code, configuration, data, or documentation changes when deciding how to verify the work. Prioritizes deterministic checks such as static analysis, formatting, linting, type checking, unit tests, integration tests, build commands, migrations, schema checks, and deterministic scripts before relying on manual inspection.
Use when writing, reviewing, or refactoring TypeScript and full-stack application code. Emphasizes clear domain models, strong type boundaries, reliable tests, observable behavior, and abstractions that fit the codebase instead of premature generalization.
Use when reviewing, designing, or rewriting user-facing error messages, validation copy, failure states, toasts, dialogs, and support paths. Helps agents make errors specific, calm, accountable, actionable, and clear about what happened and what the user can do next.