Custom API Integration & Development Services

River API is the leading UK company specialising in custom API development and integration services. We provide both internal and external solutions for the Application Programming Interface that streamline data exchange, weave complex systems, and support digital infrastructure across departments, platforms, or third-party tools.

Our dedicated software engineers create scalable API solutions and seamlessly integrate them into your existing architecture. Along with API development & integration services, River API also provides structured documentation, so your next team can onboard faster, understand dependencies from the go, and maintain the system without struggling through legacy code.

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Our custom API development services

Custom API Development

At River API, we build custom APIs designed to last under high traffic. Every line of code is written to handle real users, real load, and real change. From defining clean endpoints to setting up scalable authentication and data structures, we deliver APIs that are easy to consume, hard to break, and built for the long run.

Custom API Integration

Our API engineers integrate custom APIs into the necessary systems in a way that keeps your data flowing cleanly and your workflows stable. Forget about failed connections or unpleasant surprises when a vendor pushes an update. Our custom API integrations are built to work now and scale later.

API Modernisation and Optimisation

If your custom APIs were built for yesterday’s traffic and today’s users are outgrowing them, River API knows how to fix that. We audit, refactor, and rework legacy APIs to make them faster, safer, and easier to maintain, without forcing a full rebuild unless it’s truly necessary.

Ready to lay the groundwork for your next big win? Let’s translate your vision into a scalable custom API solution.

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Our Tech Stack

Our Custom API Integration and Development Process

Uncover what’s slowing you down

Before River API developers write a single line of code, they get clear on how your systems are currently working. That means tracing brittle integrations, misaligned endpoints, or gaps between what your apps need and what your APIs deliver.

Map the right solution, not just a new one

A clean interface isn’t enough. Our devs define how your services should communicate, what data they need, and how to keep things stable under real-world load. Every design decision is backed by a real-world use case.

Build APIs that behave well under real pressure

Our engineers write for stability, in mind with those who will maintain the system in future. That means smart versioning, robust data structures, and code that’s testable and maintainable, not stitched together in a crunch.

Validate before it breaks something

We test with intent. Load, edge cases, fallback behaviour: everything that turns “it worked in staging” into “it’s live and stable.”

Continuous support & maintenance

Once the API is launched, River API doesn’t vanish in thin air. Monitoring, logging, and documentation that remains clear and usable, so your team can scale the service without micromanaging it.

FAQ: Custom API Development & Integration Services in the UK

What is API?

An Application Programming Interface (API) is used by software engineers to enable access from one app, system, or platform to another or to integrate different applications.

There are different types of APIs:

Application APIs: Power apps like Google Maps, Facebook, Twitter, and LinkedIn
Web APIs: Enable integrations for web-based platforms like Amazon and eBay
Operating System APIs: Manage interactions with systems like POSIX (Linux/BSD) and Microsoft Windows API
Database APIs: Allow applications to communicate with database systems
Hardware APIs: Facilitate communication between software and physical devices

Software Library APIs: Expose functions and routines from software libraries for easier development

What are API integration services?

API integration services connect different software systems, tools, and platforms so they can share data, trigger actions, and work together automatically. Instead of manually moving information between apps, APIs handle communication behind the scenes, syncing customer data, processing transactions, updating records, and more.

API integration services focus on planning, building, and maintaining these connections so everything stays reliable, secure, and scalable as your business grows.

What are the benefits of building APIs for API owners?

When a business owner builds his own API, he keeps full control over how his technology is used and accessed. Instead of distributing open-source libraries that expose the code, you can offer access through a secure web API, protecting your intellectual property while still monetising the functionality.

Building a custom API also opens the door to selling high-performance features, like machine learning models or advanced processing tools, to users who don’t have the heavy infrastructure to run them locally. With an API, customers can tap into powerful back-end systems straight from their everyday devices: no specialised hardware required.

How long does a custom API development project usually take?

Timelines of an API development directly depend on the project’s complexity, as well as how tangled your systems are and how well the project requirements are scoped. A clean, well-defined API can be built and integrated in a few weeks. If we’re connecting multiple legacy platforms or rebuilding broken workflows, expect a bit longer. River API will tell you the estimates upfront, not halfway through the project’s life cycle.

Can you fix an API that’s already built but keeps causing problems?

Yes. A lot of our API projects include stepping in after "it should have worked." We audit the code, diagnose the real issues (not just the symptoms), and either repair, refactor, or rebuild based on what’s smartest for your business, not what’s easiest for us.

Will we get API documentation?

Yes, you will get real documentation. No forgotten Notion pages, no half-filled Postman collections. You’ll get clear, updated docs that any competent developer can pick up six months from now without needing a 2-hour walkthrough.

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Ready to build cleaner integrations, stronger APIs, and systems that won’t crumble when you scale? Let’s make it happen.

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