fsharp-validation

Error accumulation validation collects all field violations into a list rather than failing on the first error. This Skill implements validators that gather multiple errors across required fields, length constraints, ranges, patterns, and cross-field rules, returning them together so clients see the complete picture of what needs fixing.

Yes, this Skill supports async validation for scenarios requiring database lookups or external checks. It integrates asynchronous validators alongside synchronous field checks, enabling uniqueness constraints and cross-system validation while maintaining error accumulation across all validation types.

Apply centralized validation logic at your API boundary using field validators for individual constraints and aggregate validators for cross-field rules. This Skill provides email, URL, length, range, and pattern validators pre-built in Validation.fs, ready to integrate into create and update request handlers.

Cross-field validation checks relationships between multiple fields—for example, ensuring an end date follows a start date. This Skill includes multi-field validator patterns that evaluate related fields together and accumulate constraint violations alongside single-field errors in a unified result.

This Skill provides validateCreateRequest as the primary pattern, applicable to both create and update flows at the API boundary. The same field and async validators adapt to different request types, and you apply them consistently to enforce business rules for both operations.

Beyond required and format checks, this Skill covers range validation, pattern matching with regex, async uniqueness verification, and complex business rules enforced across fields. It accumulates errors from all scenarios simultaneously, surfacing complete validation feedback in one response.