Custom API development is the practice of building dedicated interfaces that let your separate software systems share data automatically. For UK SMEs, a custom API connects your CRM to your accounting platform, your e-commerce store to your inventory, and your mobile app to your backend, eliminating manual data entry. We build secure, well-documented REST and GraphQL APIs with authentication and rate limiting, so your systems communicate reliably and on your terms. From £5,000, fixed-price, you own the code.
Custom API development is the practice of building dedicated interfaces that let your separate software systems share data automatically. For UK SMEs, ajairu.dev builds custom APIs with authentication, rate limiting, documentation, and monitoring, connecting your CRM, accounting, ERP, and e-commerce platforms. Fixed-price from £8,000 with delivery in 4 to 8 weeks.
No jargon. Here is what an API actually does and why your business probably needs one.
An API (Application Programming Interface) is a way for two pieces of software to talk to each other. Think of it as a waiter in a restaurant. You (the customer) tell the waiter what you want. The waiter takes your order to the kitchen (the system) and brings back your food (the data). You do not need to know how the kitchen works - you just need to know what to ask for.
In business terms, an API lets your website talk to your payment processor, your CRM talk to your accounting software, or your mobile app talk to your database - automatically, without a human in the middle. When you see "Login with Google" or "Pay with PayPal," that is an API at work. For UK SMEs, a custom API means your systems can share data with each other and with your partners, suppliers, and customers - on your terms, with your rules. It also means you are not dependent on third-party integration platforms that charge per-transaction fees, store your data on their servers, and disappear when they go out of business. Your API is your infrastructure, under your control, built for your specific needs.
Off-the-shelf integrations only get you so far. A custom API gives you control, security, and flexibility.
Off-the-shelf integration tools like Zapier only connect systems that have pre-built connectors. A custom API lets you connect any system to any other system - even legacy software with no public API. If data exists in a machine-readable format, we can build an API to share it.
When you use third-party integration platforms, your data flows through someone else's servers. A custom API keeps your data on infrastructure you control, with security policies you define. For UK SMEs handling customer data under GDPR, that level of control matters.
If your customers or partners want to integrate with your system, a public API turns your software into a platform. That means stickier customers, new revenue streams, and a competitive moat. We build APIs that developers actually want to use - with clear documentation and predictable behaviour.
Two approaches to building APIs. We help you choose the one that fits your business - not the one that is trendy.
Best for: Most business applications, public APIs, and systems that need broad compatibility.
REST is the industry standard for APIs. It uses standard HTTP methods - GET to retrieve data, POST to create, PUT to update, DELETE to remove. Each endpoint (URL) represents a resource (a customer, an order, an invoice). REST is simple, well-understood, easy to cache, and supported by every programming language and integration tool on the planet.
When to choose REST: You are building a public API, connecting standard business systems, or want maximum compatibility with third-party tools. This is the right choice for 90% of UK SMEs.
Cost: From £5,000
Best for: Mobile apps, complex data relationships, and clients that need flexible queries.
GraphQL lets the client ask for exactly the data it needs - no more, no less. Instead of calling three endpoints to get a customer's details, orders, and invoices, you make one request that asks for all three. This reduces network traffic and gives front-end developers precise control over data fetching.
When to choose GraphQL: You are building a mobile app, have complex data relationships, or your front-end needs different data shapes on different screens. Not necessary for most standard business integrations.
Cost: From £7,000
Not sure which architecture fits your project? The free discovery call will clarify this in 30 minutes. Book yours now.
Security is not an add-on. Every API we build includes these protections as standard.
API keys, OAuth 2.0, or JWT tokens. Every request is verified - no anonymous access unless you specifically allow it.
Prevent abuse and protect your servers. Requests are limited per client, per time window. Customisable thresholds for different users.
Every input is validated against strict schemas. No SQL injection, no XSS, no malformed data reaching your database. OWASP guidelines followed.
Every request is logged - who called what, when, and what happened. Essential for compliance, debugging, and security investigations.
An API without documentation is like a door without a handle. We make sure your API is usable from day one.
Most API development projects fail not because the API is bad, but because the documentation is. Developers cannot figure out how to use it, integration takes weeks instead of hours, and the API sits unused while your team works around it. We treat documentation as a first-class deliverable, not an afterthought.
Every API we build ships with interactive OpenAPI (Swagger) documentation that lets developers test endpoints directly in the browser. Code examples in JavaScript, Python, PHP, and cURL. A getting-started guide that walks through authentication and the first API call. Error code reference with explanations and resolution steps. Rate limit documentation. And because the documentation is generated from the API specification, it is always in sync with the code - never out of date.
Swagger UI lets developers send real requests and see real responses in the browser. No Postman setup, no guessing. Try an endpoint, see the result, copy the code. Documentation that developers actually want to use.
Copy-paste code examples in JavaScript, Python, PHP, and cURL for every endpoint. Developers integrate in minutes, not days. Whether your consumer is a front-end developer, a data scientist, or a third-party partner, they have what they need.
Documentation is generated from the OpenAPI specification, so it is always current. When the API changes, the docs update automatically. No stale documentation, no "the docs say one thing but the API does another" - a common problem that wastes hours of developer time.
A proven 4-step process that de-risks every API project.
We map your systems, data flows, and integration requirements. We identify what the API needs to do, who will consume it, and what security constraints apply. No assumptions - we understand your exact needs.
We design the API contract - endpoints, request/response formats, authentication, and error handling. You see the full specification before any code is written. Developers know exactly what they are building against.
We build the API using AI-accelerated development. You get weekly demos, automated tests, and interactive documentation (Swagger/OpenAPI). Test against real data in a staging environment throughout.
We deploy to production with monitoring, alerting, and rollback procedures. Your team gets full documentation, SDK examples, and 30 days of post-launch support. You own all the code.
Fixed-price engagements. You know the total cost before we start. No day rates, no surprise billing.
All prices are fixed - you approve the scope before we start. See all our bespoke software development services or book a free discovery call.
Full source code, API specification, and documentation. No licence fees, no vendor lock-in. Your developers can extend and maintain the API independently. The API is an asset you own, not a service you rent.
Every API ships with interactive OpenAPI/Swagger documentation, code examples in multiple languages, and a getting-started guide. Developers can test endpoints in the browser. No more guessing how the API works - it is all there, clearly written.
Authentication, rate limiting, input validation, and audit logging are built in from day one. We follow OWASP guidelines and can add IP allow-listing, request signing, and GDPR-compliant data handling. Security is not an afterthought.
Straight answers to the questions UK SMEs ask us about API development.
A single custom API with authentication and documentation starts from £5,000. A multi-endpoint API suite with rate limiting and integration support typically costs £10,000 to £18,000. Full enterprise API platforms with developer portals, OAuth, and monitoring range from £20,000 to £35,000+. All projects are fixed-price - you know the total cost before we start.
An API (Application Programming Interface) is a way for two pieces of software to talk to each other. Think of it as a waiter in a restaurant - you (the customer) tell the waiter what you want, the waiter takes your order to the kitchen (the system), and brings back your food (the data). You do not need to know how the kitchen works - you just need to know what to ask for. APIs let your website talk to your payment processor, your CRM talk to your accounting software, or your mobile app talk to your database.
It depends on your use case. REST is the industry standard - well-understood, widely supported, and ideal for most business applications. It uses standard HTTP methods (GET, POST, PUT, DELETE) and is easy to cache and scale. GraphQL is better when you have complex data relationships and clients that need flexible queries - for example, a mobile app that needs different data shapes on different screens. We help you choose based on your specific requirements, not fashion.
Every API we build includes authentication (API keys, OAuth 2.0, or JWT tokens), rate limiting to prevent abuse, input validation to prevent injection attacks, HTTPS encryption, and CORS policies. We follow OWASP security guidelines and can add IP allow-listing, request signing, and audit logging for sensitive applications. Security is built in from the start, not bolted on.
Yes, entirely. You own the source code, the API specification, and all documentation from day one. No licence fees, no vendor lock-in. Your developers can extend and maintain the API independently, or we can provide ongoing support from £350/month. You are never trapped with a single supplier - the API is yours.
Book a free 30-minute discovery call. We will map your systems, identify the integrations that will deliver the most value, and give you a fixed-price quote - whether you need a single endpoint or a full API platform.