Building an MVP quickly is a top priority for startups and entrepreneurs—but speed shouldn’t come at the expense of consistency. As a freelance full-stack engineer working with .NET, Node.js, Laravel, and iOS (Swift), I often see clients struggle when their web and mobile apps drift apart. Duplicate validation rules, mismatched workflows, and subtle bugs can creep in, slowing down delivery and eroding trust.

Why Shared Business Logic Matters 🔄

Imagine you’ve coded a discount rule in your .NET Core backend. Meanwhile, your iOS app implements the same rule in Swift. A minor tweak—say, changing the eligibility date—forces you to update two codebases. Miss one, and users get inconsistent experiences, customer support tickets skyrocket, and your reputation takes a hit.

• Accelerate development: Write logic once, reuse everywhere.
• Ensure consistency: Single source of truth for rules and validation.
• Reduce bugs: Eliminate human error from manual duplication.

By sharing business rules across platforms, you deliver reliable features faster, impress stakeholders, and focus on building value, not firefighting.

Strategies for Sharing Validation and Rules

There are several approaches to unify your logic. Here are the most practical ones I’ve used with clients:

1. JSON Schema for Validation
   Define your data models and validation rules in a JSON Schema file. Use AJV in Node.js, JsonSchema.Net in .NET, and JSONSchema.swift in Swift to enforce the same rules everywhere.
2. OpenAPI (Swagger) Codegen
   Publish your API contract with OpenAPI. Generate client SDKs for .NET, JavaScript/TypeScript, and Swift. This ensures request and response models align perfectly, reducing integration issues.
3. GraphQL with Typed Clients
   Use GraphQL for flexible queries and Apollo iOS or GraphQL.NET to generate strongly-typed code. Shared schemas keep your mobile and web UIs in sync with the backend.
4. gRPC or Protocol Buffers
   For high-performance scenarios, define your service contract in a .proto file. Generate both .NET and Swift clients. gRPC ensures wire-protocol consistency and faster transport.

Real-World Implementation: A Case Study

Recently, I helped a health-tech startup launch a telemedicine app on a tight schedule. They needed:

• Data validation for appointment slots and patient info
• Pricing logic for subscription tiers
• Role-based access control

Here’s how we tackled it:

1. Created a shared JSON Schema repo in GitHub.
2. Integrated AJV in the Node.js appointment microservice and JsonSchema.Net in the .NET billing API.
3. Used JSONSchema.swift in the iOS codebase to validate forms locally before sending requests.
4. Automated updates via a CI pipeline—every pull request ran schema tests.

The result? Zero validation inconsistencies in production, a 30% reduction in QA cycles, and the client hit their launch date with confidence.

Tips for Freelancers Managing Overlapping Codebases

Based on my experience, here are practical tips to keep your sanity (and your clients happy):

• Version your schemas: Treat them like any other API—you’ll need backward compatibility and clear migration paths.
• Automate tests: Use GitHub Actions or Azure Pipelines to validate schema changes in each language before merging.
• Document clearly: Provide examples in each repo, so new collaborators understand how to consume the shared logic.
• Start small: Roll out shared validation for one business entity, then expand once the pipeline is solid.

Conclusion & Next Steps 🚀

Sharing business rules across .NET, Node.js, and iOS can transform your MVP development. You’ll move faster, ship features more confidently, and wow clients with polished, reliable experiences. Whether you’re building a startup MVP or scaling an existing digital product, this unified-logic approach pays dividends in the long run.

Ready to streamline your development workflow and deliver consistent, high-quality apps across platforms? Let’s chat! Visit ureymutuale.com or drop me a line at [email protected]. You can also connect on LinkedIn and follow me on Twitter @urey_mutuale.