What to Look for in an App Developer’s Portfolio (And Why Screenshots Aren’t Enough)

When evaluating a mobile app developer’s portfolio, look for: live, downloadable apps in the App Store or Google Play that you can test personally; apps with four stars or higher and substantive recent reviews indicating real user value; portfolio variety covering different industries, platforms, and technical complexity levels; evidence of apps that have been live for more than 12 months (indicating quality that has stood the test of time); and case studies that explain the technical challenges solved, not just how the finished app looks.

Screenshots and mockups in a portfolio can be misleading — they can show polished designs that were never shipped, hide performance issues, or represent work done by a different team member than the one who will build your app. Testing a live portfolio app reveals actual performance, UI quality, stability, navigation patterns, and load times — all of which are direct indicators of what your app will feel like. An agency that points you only to screenshots rather than live downloadable apps should be treated with caution.

To evaluate technical quality of a portfolio app, test: startup time (should be under 1.5 seconds for a good impression), scrolling and animation smoothness (should be consistently 60fps), navigation responsiveness (taps should register immediately with no lag), offline behaviour (what happens when you enable aeroplane mode), and App Store rating and review quality (particularly reviews that mention technical issues). You can also ask the agency to walk you through their code architecture and testing approach for a portfolio app — the clarity and depth of their answer is revealing.

An app development case study is a structured account of a completed project that explains the client’s challenge, the solution developed, the technical approach taken, the process followed, measurable outcomes achieved, and any significant challenges overcome during the project. A strong case study includes: the client name and industry (or anonymised description if under NDA), the platform (iOS, Android, cross-platform), the development timeline and team size, specific technical challenges and how they were resolved, App Store rating and user metrics where available, and a client quote or reference contact.

Relevant industry or technical experience in a portfolio is valuable but not essential. An agency with a strong portfolio of complex apps in adjacent sectors brings transferable architectural and UX knowledge that outweighs sector-specific familiarity in most cases. However, for projects in regulated industries (healthcare, fintech, legal), relevant compliance and integration experience is genuinely important and worth prioritising. For specialist needs — real-time matching systems, clinical decision support, or financial transaction processing — ask specifically about analogous technical experience rather than sector match.

Many agencies do a significant proportion of their best work under non-disclosure agreements (NDAs) that prevent them from naming clients or showing specific features publicly. This is legitimate and common — enterprise clients and funded startups often require confidentiality. However, be cautious of agencies whose entire portfolio is ‘NDA protected’ with no verifiable public work — this can be a shield for a weak portfolio. A credible agency should have at least some public work visible in the App Store, even if their best projects are under NDA.

agency with 10 live, high-quality, recent apps that you can download and test is more impressive than one with 100 portfolio items that are mostly screenshots or apps that are no longer live. For a UK-based app agency with more than five years in business, a portfolio of 15 to 30 live, downloadable apps across varied categories is a reasonable expectation. Ask specifically when each app was built and whether it is still active.

Client references are past clients who have agreed to speak directly with prospective clients about their experience working with the agency. They are one of the most valuable due diligence tools available and significantly more informative than testimonials on the agency’s own website. When speaking with a reference, ask: Did the agency deliver on time and on budget? How did they handle scope changes and unexpected challenges? Would you use them again? What was the communication quality like day to day? Were there any significant problems, and how were they handled?

Stakk has built over 100 mobile applications across iOS, Android, and cross-platform over 12 years. Our portfolio spans fintech, healthcare, eCommerce, logistics, EdTech, property, and enterprise tools. Director Jack Tyson brings 12 years of hands-on development leadership to every client engagement — not just commercial oversight. We are happy to share relevant portfolio examples, provide App Store links to live apps, and connect prospective clients directly with past clients for reference calls. Free consultation available to discuss your specific project requirements.