API Development & Integration | REST, GraphQL & Microservices

Modern business runs on connected systems. Your CRM needs to talk to your accounting software. Your e-commerce platform needs to sync inventory with your warehouse management system. Your mobile app needs real-time data from multiple backend services. APIs are the connective tissue of digital business — and when they're built properly, they unlock automation, enable innovation, and eliminate manual data entry.

We build production-grade APIs and integration layers that connect your systems reliably, securely, and at scale. Whether you're exposing data to partners, integrating third-party services, or modernising legacy systems with an API-first approach, we deliver solutions that just work.

Why API architecture matters: The business case

Poorly designed APIs create expensive problems:

• Data silos cost money. When systems can't talk to each other, staff waste hours on manual data entry. A UK manufacturing client was spending 15 hours per week copying order data between their ERP and e-commerce platform. Our REST API integration eliminated that entirely — saving £32,000 per year in staff time and cutting order processing errors by 94%.
• Slow integrations lose customers. A fintech startup we worked with had a payment gateway integration that took 8-12 seconds to return a response. Checkout abandonment was 31%. We rebuilt the integration with proper async processing and caching — response time dropped to 450ms, abandonment fell to 9%, increasing completed transactions by £180,000 per month.
• Poor API design compounds technical debt. Every breaking change ripples through every client. A SaaS company we advised had accumulated 14 different API versions over 4 years. Maintaining them consumed 40% of backend capacity. We designed a single unified GraphQL API with proper versioning — reducing support tickets by 60% and freeing the team to ship features instead of patching integrations.
• Security vulnerabilities scale with API surface area. APIs are attack vectors. Without proper authentication, rate limiting, and audit logging, every endpoint is a potential breach point. We've rescued three projects where inadequate API security led to data exposure incidents — one resulted in a £47,000 ICO fine.

The alternative: Well-designed APIs become competitive advantages. They enable automation, partner ecosystems, mobile experiences, and real-time analytics. They make change cheaper and faster. They turn your software into a platform.

Our API development capabilities

RESTful API Development

We build production-grade REST APIs following industry standards:

• Proper HTTP semantics — GET for reads, POST for creates, PUT/PATCH for updates, DELETE for removes. Correct status codes. Meaningful error responses.
• Versioning strategies — URL versioning (/v1/orders), header-based versioning, or content negotiation. Deprecation policies that give clients time to migrate.
• Authentication & authorisation — OAuth 2.0, JWT tokens, API keys, role-based access control (RBAC).
• Rate limiting & throttling — Protect your infrastructure from abuse. Redis-backed token bucket algorithms or API gateway policies.
• Comprehensive documentation — OpenAPI (Swagger) specs, interactive API explorers, code examples in multiple languages.
• Pagination, filtering, sorting — Efficient data retrieval for large datasets. Cursor-based pagination for real-time feeds.

Real example: We built a REST API for a logistics company that exposes shipment tracking data to 40+ retail partners. The API handles 2.3 million requests per day, returns results in <150ms at p99, and has maintained 99.97% uptime over 18 months.

GraphQL Implementation

For clients that need flexible data fetching, GraphQL eliminates over-fetching and under-fetching:

• Type-safe schemas — Define your data model once. Clients get autocomplete and validation.
• Efficient data fetching — Request exactly the fields you need. One round trip replaces multiple REST calls. Mobile apps use 40-60% less bandwidth.
• Real-time subscriptions — WebSocket-based subscriptions for live updates. Perfect for dashboards and collaborative tools.
• Federation & schema stitching — Combine multiple GraphQL services into a unified API gateway.

Real example: A property tech startup replaced 6 separate REST APIs with one federated GraphQL API. Frontend teams ship features 3× faster. The API serves 800,000 queries per day with a median response time of 85ms.

Third-Party Integration

Most business software doesn't exist in isolation. We connect your systems to the tools you already use:

• Payment processors — Stripe, PayPal, GoCardless, Worldpay. We handle webhooks, idempotency, retry logic.
• CRM & Marketing — Salesforce, HubSpot, Mailchimp. Sync contacts, deals, and campaign data bidirectionally.
• ERP & Accounting — Xero, QuickBooks, SAP, NetSuite. Automate invoice creation and expense tracking.
• Cloud storage & documents — AWS S3, Google Drive, Dropbox, SharePoint.
• Communication platforms — Slack, Microsoft Teams, Twilio. Send notifications, trigger workflows.

Real example: An e-commerce company needed to sync orders from Shopify to Xero, send shipping labels via Royal Mail API, notify warehouse staff via Slack, and trigger email receipts via SendGrid. We built an event-driven integration platform using AWS Lambda and SQS. It processes 4,000 orders per day and saves the finance team 12 hours per week.

Legacy System Integration

Not every system has a modern API. We build bridges to legacy platforms without rewriting them:

• Database-backed APIs — Expose legacy SQL Server, Oracle, or DB2 databases via REST or GraphQL.
• SOAP to REST translation — Wrap old SOAP services with clean REST APIs. Hide XML complexity behind JSON interfaces.
• Mainframe & AS/400 integration — Connect via MQ Series, CICS, or direct database access.
• Adapter pattern — Build a modern API layer that talks to legacy systems internally but exposes a clean interface externally. Migrate the backend later without breaking clients.

Real example: A financial services firm had 15 years of customer data in a legacy SQL Server 2008 database. We built a GraphQL API that abstracted the database complexity, implemented Redis caching, and provided a clean data model. New features that used to take 6 weeks now ship in 2-3 days.

Case study: Fintech payment gateway integration

Challenge: A UK-based fintech startup needed to integrate Stripe for card payments, GoCardless for Direct Debit, and Xero for accounting reconciliation. Their in-house integration was taking 8-12 seconds per transaction, causing 31% checkout abandonment.

What we did:

• Rebuilt the integration as async workflows — response time dropped from 8-12s to 450ms
• Implemented idempotency using idempotency keys so customers aren't charged twice
• Added retry logic with exponential backoff for temporary failures
• Reconciliation automation — every successful payment creates an invoice in Xero via their API

Results:

• Checkout abandonment dropped from 31% to 9% — an additional £180,000 per month in completed transactions
• Payment processing errors fell by 94%
• Finance team saves 8 hours per week on manual Xero data entry
• Full ROI achieved in 6 weeks

How we deliver API projects

1. Discovery & API design

Before we write code, we map your integration needs:

• Stakeholder workshops — Who are the API consumers? What do they need to do?
• Use case mapping — Define the key workflows
• Data model design — What entities exist? What relationships?
• API contract definition — OpenAPI specs or GraphQL schemas before implementation

2. Agile implementation

We build in two-week sprints. Every sprint includes automated tests, API documentation updates, and a demo environment.

3. Security & performance hardening

Before production launch, we conduct load testing, penetration testing, rate limiting configuration, and monitoring setup.

4. Developer experience

APIs are products. We make them easy to use with interactive documentation, code examples in multiple languages, Postman collections, and SDK generation.

Why businesses choose iCentric

• We understand the business context. We've built APIs for healthcare, logistics, fintech, e-commerce, and PropTech. We ask business questions first and technology questions second.
• Production-ready from day one. Our APIs average 99.9%+ uptime with proper error handling, idempotency, circuit breakers, and graceful degradation.
• We make change cheap. Well-designed APIs with proper versioning, backward compatibility, and automated testing reduce future costs.
• Security & compliance built in. OWASP Top 10 mitigation, GDPR compliance, SOC 2 & ISO 27001 alignment, encrypted data in transit and at rest.

Technology we use

API frameworks & languages: Node.js (Express, Fastify, NestJS), Python (FastAPI, Django REST Framework), .NET Core (ASP.NET Core Web API), Go, GraphQL (Apollo Server, Hasura, AWS AppSync).

Authentication & security: OAuth 2.0 / OpenID Connect (Auth0, Okta, AWS Cognito), JWT tokens, API keys, HMAC signatures, rate limiting (Redis, AWS API Gateway throttling).

API gateways & service mesh: Kong, Tyk, AWS API Gateway, Azure API Management, Istio, Linkerd.

Messaging & webhooks: RabbitMQ, Kafka, AWS SNS/SQS, Azure Service Bus, webhook delivery with retry logic and signature verification.

Documentation & developer experience: OpenAPI (Swagger), Redoc, Stoplight, GraphQL Playground, Postman collections.

Get in touch

Ready to build APIs that unlock automation, enable partnerships, and eliminate manual data entry?

Book a free consultation — we'll discuss your integration requirements, map your existing systems, and provide a proposal and timeline within 48 hours.

Typical project timelines:

• Simple REST API (5-10 endpoints): 4-6 weeks
• GraphQL API with federation: 8-12 weeks
• Legacy system modernisation (API wrapper): 6-10 weeks
• Third-party integration (payment, CRM, ERP): 2-4 weeks