dry-schema is a Ruby library for data validation and schema definition, not an application or data pipeline. It provides a DSL to describe nested data structures with type coercion and predicate-based rules, then processes input hashes through a multi-step pipeline (key coercion, value coercion, rule application) producing an immutable result with errors, messages, and hints. It exposes Dry::Schema.define for plain schemas, Dry::Schema.Params for HTTP parameter coercion, and Dry::Schema.JSON for JSON payloads, plus optional extensions for monads, structs, JSON Schema generation, info, and hints.