The Problem

Your systems don't talk to each other. Customer data lives in one place, order data in another, and financial data in a third. Your team spends hours each week manually exporting CSVs, copying data between systems, and reconciling discrepancies. When a new system needs data from an existing one, someone builds a quick integration that works until it doesn't — and then breaks silently.

Or you need to build an API for a new product or service, but you're not sure how to design it for scale, handle authentication properly, or make it reliable enough for external consumers to depend on. You need someone who's built APIs that handle real production traffic and understands the difference between a prototype and a production system.

What You Get

Well-documented, thoroughly tested APIs that your team and partners can rely on. I follow REST best practices, implement proper authentication using OAuth 2.0, API keys, or JWT depending on your use case, handle versioning so existing consumers aren't broken by changes, and include comprehensive Swagger/OpenAPI documentation that developers can use without needing to ask questions.

For integrations, you get reliable connections between your systems that handle failures gracefully. When a third-party API goes down — and it will — your integration retries, logs the failure, and alerts your team instead of silently dropping data.

Common Projects

The integration and API work I do most often includes building API backends for web and mobile applications with proper authentication, rate limiting, and monitoring, integrating with payment providers such as Stripe and GoCardless for billing automation, connecting CRM systems like Dynamics 365 or Salesforce to internal tools and databases, implementing government service integrations including GOV.UK Notify for email and SMS, GDS APIs, and Companies House lookups, data synchronisation between legacy systems and modern platforms where real-time or near-real-time consistency is required, and building webhook receivers and event-driven integrations using Azure Service Bus or RabbitMQ.

APIs consumed by external developers need clear documentation, a compatibility policy and a way to communicate changes. Agree these requirements alongside authentication, monitoring and support arrangements.

How I Build Reliable Integrations

APIs fail. Third-party services go down. Networks are unreliable. I build for this reality using a set of patterns that ensure your integrations degrade gracefully rather than failing catastrophically.

Retry policies need bounded attempts, backoff and operation-specific rules. A timeout can occur after an operation succeeded, so retrying a write requires idempotency or duplicate detection. Microsoft's retry guidance explains these trade-offs. Circuit breakers limit repeated calls to failing dependencies. Health checks and structured logs help diagnosis, with sensitive fields redacted and retention agreed for the service.

API Design Principles

Good API design makes the difference between an API that developers love and one that generates endless support tickets. I follow a consistent set of principles: resource-oriented URLs that are intuitive without documentation, consistent error responses that include error codes, messages, and guidance on how to fix the issue, pagination for list endpoints so large datasets don't overwhelm consumers, proper use of HTTP status codes so clients can implement reliable error handling, and versioning from day one so you can evolve the API without breaking existing consumers.

I include Swagger/OpenAPI documentation generated from the application. Generated documentation still needs review and integration tests to check that examples, error responses and authentication requirements match the delivered behaviour.

Technologies

ASP.NET Core Web API, Minimal APIs, HttpClientFactory, Polly for resilience, MassTransit for message-based integration, Azure Service Bus, Azure Functions for event-driven processing, Swagger/OpenAPI, OAuth 2.0, JWT, Azure API Management for external-facing APIs, and Application Insights for monitoring and diagnostics.

Pricing

Simple API development — a straightforward CRUD API with authentication and documentation — starts from £3,000. Complex integrations involving multiple third-party systems, data transformation, error handling, and monitoring typically range from £5,000 to £15,000. Projects are priced individually after a detailed requirements review where I understand the systems involved, data volumes, and reliability requirements.

I provide a fixed-price quote before work begins. If you need ongoing maintenance of integrations after delivery, I offer retainer arrangements at a discounted rate.

Discuss Relevant Work

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🔗 API & Integration Development