Write and ship modern custom RuboCop cops in 2026: learn the new plugin system, requires_gem API, InternalAffairs best practices, safe autocorrection nuances, and design trade-offs for building robust, future-proof lint rules.

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Martian Chronicles

An updated guide to writing custom RuboCop cops in 2026, covering the new plugin system based on lint_roller, the rubocop-internal_affairs department for linting cop implementations, the requires_gem API for gem-conditional cops, nuances of safe vs. unsafe autocorrection, and design trade-offs around using runtime information in static analysis. The post revisits a 2021 article and highlights deprecated APIs (e.g., inheriting from RuboCop::Cop::Cop instead of Base) and best practices for publishing reusable RuboCop plugins.

Writing custom RuboCop rules in 2026—Martian Chronicles, Evil Martians’ team blog

Custom "cops" for RuboCop: an emergency service for your Ruby code