Target audience

Spine Validation is designed for developers who model data and APIs using Protocol Buffers and need a structured, type-safe way to express and enforce constraints on that data.

The library serves several overlapping groups:

1. Application developers 

Developers building backend services in Java or Kotlin who need validation for:

  • incoming API requests (REST / gRPC),
  • commands and events,
  • domain objects stored in persistence,
  • user-generated data.

These developers benefit from:

  • concise .proto-based validation rules,
  • generated validation code,
  • unified constraints across all layers of the application.

This group typically works directly with generated message builders and calls validate() at appropriate points in their workflow.

2. Teams using the Spine Event Engine 

Spine Validation is the standard validation mechanism used inside the Spine Event Engine.
Teams who adopt Spine for CQRS/ES applications already rely on the runtime to validate:

  • commands,
  • events,
  • value objects within aggregates and processes.

For Spine users, this library provides:

  • consistent validation semantics across the entire model,
  • rich domain-focused constraints,
  • cross-field and message-level validations.

3. Framework and platform integrators 

Engineers who build frameworks, platforms, or infrastructure around Protobuf often need to enforce rules across:

  • transport layers,
  • boundary adapters,
  • persistence and serialization,
  • API gateways.

For these integrators, Spine Validation provides:

  • predictable validation lifecycle,
  • well-structured diagnostics (ValidationException, error trees),
  • hooks for custom validators,
  • extension points via custom validation options.

4. Library authors and tooling developers 

Those who maintain shared data models across a large organization can use Spine Validation to:

  • standardize validation behavior for all services,
  • define custom domain-specific validation options,
  • generate validator code for multiple runtime targets.

This group interacts with advanced parts of the library such as:

  • validation model configuration,
  • option policies,
  • custom code generation units.

5. Not the target audience (explicitly) 

The library is not designed for:

  • UI-level form validation,
  • general-purpose validation of arbitrary POJOs,
  • Java Bean Validation (Jakarta Validation) replacement at the presentation layer,
  • JSON-schema or OpenAPI validation.

Spine Validation is intentionally focused on the Protobuf → runtime code pipeline and the domain layer of applications.

Summary 

If you:

  • model your data in Protobuf,
  • generate Java/Kotlin code,
  • and want to enforce clear, versionable, and strongly typed validation rules,

then Spine Validation is designed for you.

What’s next