Runtime and generation

Validator API

Generated validators implement IValidator<T>:

ValidationResult Validate(T instance);
ValueTask<ValidationResult> ValidateAsync(T instance, CancellationToken cancellationToken = default);
bool IsValid(T instance);
ValueTask<bool> IsValidAsync(T instance, CancellationToken cancellationToken = default);

Use async APIs whenever a validator graph can contain async predicates or async property validators.

Options

Option	Values	Default
Mode	Auto, Debuggable, Fast	Auto
FailureBehavior	ValidateAll, FailFast	ValidateAll
Lifetime	Scoped, Transient, Singleton	Scoped

Auto uses the runtime, debuggable backend in Debug builds and generated fast code otherwise. Debuggable lets you step through Configure; Fast always uses direct generated checks.

Choose validator lifetime based on constructor dependencies. A singleton validator must not capture scoped services.

Result model

ValidationResult exposes all failures as well as Errors, Warnings, and Infos. Only error severity makes IsValid false. Each ValidationFailure includes PropertyName, ErrorCode, ErrorMessage, and Severity.

Generator scope

[ValiantValidator] is the discovery hook. Only marked validator declarations enter the incremental pipeline. Generated output can include:

• direct sync/async IValidator<T> methods;
• metadata used by OpenAPI and integrations;
• generated DI registration through AddValiantValidators;
• composition code for root and property validators.

The marker accepts generic and typeof(...) compatibility forms. Prefer an ordinary [ValiantValidator] declaration that inherits ValidatorDefinition<T>; it is the recommended authoring surface for both fluent and attribute-based validation.

Authoring constraints

• Validator and generated containing types must be partial.
• Attribute rules must be Valiant validation attributes.
• Generator-readable expressions produce direct fast-path code; unsupported declaration shapes are compile-time diagnostics rather than runtime surprises.
• Property validators skip null property values unless presence is checked separately.