Validator Crate

The Validator Crate specification describes how data validation is modeled in Rust using derive(Validate) and field attributes. It covers typical use cases such as validating configuration structs, API payloads, and CLI inputs, with emphasis on deterministic error reporting and transparent rule composition. It explains the conceptual workflow: define a data model, attach validation attributes, and invoke validation to produce structured errors per field. It highlights nested validation for complex hierarchies and how serde deserialization interplays with subsequent validation. It also notes unique differentiators like macro-driven validation, compile-time ergonomics, and strong type safety, which reduce runtime surprises and improve maintainability. The tool identifies outputs as a per-field error map and a global result, enabling straightforward integration with downstream logic and testing. Finally, it outlines common patterns, such as cross-field validation, custom validators, and how to propagate validation context through error objects for effective debugging.

Developers benefit from a clear map of capabilities, constraints, and integration points, enabling consistent enforcement of data contracts across services, libraries, and binaries. The specification also clarifies what is out of scope, such as UI concerns or platform-specific adapters, focusing strictly on validation semantics, error structure, and integration in Rust codebases.

Use cases include validating config files loaded at startup, ensuring API payloads conform to expected shapes, and validating user input in CLIs. The document positions the validator crate as a core reliability feature that reduces runtime failures and promotes secure, predictable software behavior.