Connecting your SaaS product to third-party platforms, payment providers, CRMs, or internal systems shouldn’t mean gambling on an unreliable freelancer or waiting months for an agency to schedule you in. By Design UK is a UK-based software team offering a SaaS development and API integration service that sits between the two: fixed-price, AI-accelerated, and delivered with full source code ownership handed to you at the end.
Whether you need to integrate Stripe, Xero, HubSpot, a shipping carrier, an internal ERP, or a bespoke internal microservice, our engineers build robust, well-documented integrations that are stable in production — not brittle scripts that break the moment an upstream API changes. We treat every integration as production infrastructure, with error handling, logging, and monitoring built in from day one.
Pricing depends on the complexity of the systems involved, the number of endpoints, authentication requirements, and whether the integration sits within a wider SaaS build. As a guide, full SaaS builds involving significant API integration work typically range from £18,000 to £650,000+, depending on scope, data volume, and the number of third-party services connected. Smaller, standalone integration projects — such as connecting a Shopify storefront to an external system — are usually scoped within our Shopify services tier, priced between £499 and £18,999. We always agree a fixed price before work begins, so there are no surprise invoices halfway through the project.
Freelance developers can be fast and cheap initially, but many disappear mid-project, leave undocumented code, or retain informal ownership over what they’ve built — leaving you exposed if they become unavailable. Traditional agencies, on the other hand, are often reliable but slow, expensive, and notoriously opaque about pricing, with scope creep quietly inflating quotes as the project drags on. By Design UK is built to close that gap: a proper UK company with accountable delivery, fixed pricing agreed upfront, AI-accelerated development that compresses timelines without cutting corners, and — critically — full source code ownership transferred to you on completion. You’re never locked in to us for future changes.
We don’t just talk about building reliable software — we run one. Tackly.co.uk is a live, multi-toolkit SaaS platform designed, built, and operated by our own team, integrating multiple third-party APIs, payment processing, and user authentication in a production environment used by real customers every day. It’s a working demonstration of the same integration architecture, coding standards, and API reliability practices we bring to client projects. When you work with us, you’re not trusting a portfolio of screenshots — you’re trusting a team that maintains its own live SaaS product.
Every engagement starts with a scoping call to understand which systems need to talk to each other and why. From there we produce a fixed-price proposal covering the full integration scope, so you know exactly what you’re paying before development starts. AI-accelerated tooling speeds up boilerplate work, testing, and documentation, letting our engineers focus on the parts of the integration that genuinely require judgement — authentication edge cases, data mapping, and failure handling. You get regular progress updates, a working staging environment to review, and full source code and documentation at handover. Learn more about our approach on the about page, or get in touch via our contact page to discuss your integration requirements.
In most cases, yes. We regularly work with payment providers, CRMs, accounting platforms, logistics APIs, and bespoke internal systems. During discovery we confirm the target API’s documentation, authentication method, and rate limits before quoting a fixed price.
Yes. Full source code ownership is transferred to you at project completion, along with documentation. You are never dependent on By Design UK to maintain or modify the integration afterwards, though ongoing support is available if you want it.
Straightforward integrations can be delivered in a few weeks, while complex, multi-system integrations within larger SaaS builds take longer. Our AI-accelerated development process typically reduces timelines compared with traditional agency delivery.
We build in error handling and monitoring from the start, and offer ongoing support plans from £797/month for SaaS platforms or £299/month for Shopify integrations, covering monitoring, fixes, and updates as third-party APIs change.
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