Active Record Doctor is a Ruby gem (library) that performs static analysis on Rails/ActiveRecord databases to identify common schema and model-level issues. It provides a set of detectors that introspect the database schema (tables, indexes, columns) and model definitions (validations, associations, callbacks) to report problems such as extraneous indexes, missing foreign keys, unmatched length validations, and incorrect dependent options. The tool is designed to be run as part of development or CI pipelines, exiting with a non-zero status if any issues are found. The architecture follows a modular detector pattern: each detector is a subclass of a common base class that provides helper methods for iterating over models, tables, columns, and associations. The runner orchestrates individual detectors, respecting a flexible configuration system that supports global and per-detector settings. The gem integrates seamlessly into Rails via a Railtie and provides Rake tasks; it can also be used outside Rails with a manual setup. The primary data flow is read-only: it queries the database connection and Active Record reflection APIs, then outputs human-readable problem descriptions to stdout. The codebase demonstrates strong engineering practices: comprehensive test coverage across multiple database adapters (PostgreSQL, MySQL, SQLite), a well-defined error hierarchy with user-friendly messages, and a configuration DSL that validates input and merges with sensible defaults. The gem is actively maintained, supports recent Rails versions (7.0–8.0), and has a dedicated community (1900+ stars, 31 open issues, 68 forks).