--- title: Whats the difference between public and private APIs for apps description: Learn the real differences between public and private APIs, when to use each, and how your choice shapes security, scalability and partnerships. image: https://weareaffective.com/hubfs/learning-centre-images/whats-the-difference-between-public-and-private-apis-for-apps.webp --- [Skip to content](https://weareaffective.com/learning-centre/whats-the-difference-between-public-and-private-apis-for-apps#main-content) [![we\_are\_affective\_logo\_200](https://weareaffective.com/hs-fs/hubfs/we_are_affective_logo_200.png?width=175&height=48&name=we_are_affective_logo_200.png "we_are_affective_logo_200")](https://weareaffective.com) - [Home](https://weareaffective.com) - About Us - [Our Story](https://weareaffective.com/about) - [How We Work](https://weareaffective.com/how-we-work) - Our Services - [App Planning & Strategy](https://weareaffective.com/app-planning-strategy) - [App Design](https://weareaffective.com/app-design-agency) - [App UX Design](https://weareaffective.com/app-ux-design) - [App UI Design](https://weareaffective.com/app-ui-design) - [App Technical Architecture](https://weareaffective.com/app-architecture) - [Existing App Audits](https://weareaffective.com/app-audit) - [Case Studies](https://weareaffective.com/case-studies) - [Pricing](https://weareaffective.com/pricing) - [Learning Centre](https://weareaffective.com/learning-centre) - [Get Started](https://weareaffective.com/get-started) Expert Guide Series # Whats the difference between public and private APIs for apps Table of Contents Every app talks to something. A database, a payment processor, a map service, a music catalogue. The question is never really whether your app uses APIs, because at some level it almost certainly does. The question is which kind, built or licensed by whom, and on whose terms. Getting that wrong costs real money, real time, and sometimes the product itself. The distinction between public and private APIs sounds like a technical detail, and product teams often treat it that way, delegating it to developers while focusing on features and design. But the choice shapes [what you can build, how fast you can move](https://weareaffective.com/app-architecture-design-we-are-affective), what you owe to third parties, and how exposed your users are. On a trading platform we inherited in the drinks industry, there was no API layer at all. The system was tightly coupled, the third-party developer who built it was slow to respond, and every question about how to access data became a blocker. We ended up writing the API specification ourselves and handing it to them to implement. That is not a technical footnote. That is a month of lost momentum that a clearer API strategy at the start would have avoided. ## When a Private API Is the Right Choice A private API is the right foundation when you need to own the data model completely, when security requirements are strict, or when no suitable public API exists for what you need to do. It is also right when you are building something proprietary where exposing the interface would mean exposing competitive advantage. The case for starting with a private API is strongest when the product is complex enough that [different parts need to communicate in sophisticated ways](https://weareaffective.com/learning-centre/5-things-that-make-the-difference-between-so-so-apps-and-stellar-apps-what-your-). A product with a mobile app, a web dashboard, and an admin panel all drawing on the same data source benefits from a well-designed private API from early on, because without it, each client ends up making direct database calls, which becomes a maintenance and security problem quickly. If your product has more than one client type talking to the same data, define even a minimal private API before you build the second client. Retrofitting one later costs more than starting with it. The Firebase approach we used on the survey app worked for a proof of concept, but the security trade was real. With no API layer acting as a controlled intermediary between the client and the database, we had to scrutinise every Firebase security rule with unusual care to ensure neither the app nor the web response page could be exploited. That kind of manual rule management is manageable at MVP scale. It becomes a liability as the product grows and the surface area expands. ## When a Public API Opens Doors You Actually Want Open Public APIs are the right choice when a third-party platform already holds something your users want and you do not need to replicate it. Music catalogues, payment rails, mapping data, identity verification, these are things that took years and enormous resources to build. A public API gives you access to that infrastructure for the cost of integration work and ongoing fees. The Deezer integration on the memory-sharing project is a good example of a public API doing exactly what it should. We did not need to license music, manage a catalogue, or handle playback infrastructure. Deezer had all of that. We called their API, surfaced their catalogue inside our product, and the user experience was indistinguishable from something built in-house. The additional benefit was that when a user wanted the full track rather than the clip, there was a natural upsell to a Deezer subscription, creating affiliate referral revenue as a secondary income stream alongside the core product. Working with a public API in the way the provider intends also simplifies compliance. By using Deezer's official API as designed, we were fully compliant with their terms without needing workarounds. Working around Spotify without a proper API, by contrast, would have required significant custom solutions and carried compliance risk throughout. The cleaner path was not the obvious one at the start, but it became clear once we understood what each provider's API actually supported. Before committing to a third-party integration, read the API's terms of service for commercial restrictions. Some public APIs prohibit certain use cases even for paying customers, and discovering that mid-build is expensive. ## What Happens When You Skip a Formal API Layer Altogether Some early-stage products skip a formal API entirely. The app talks directly to the database, or components share state through other means. This is almost always a short-term saving that becomes a long-term cost. On the drinks industry trading platform we inherited, there was no API layer. The web product was tightly coupled, with everything running through a third-party developer who owned the codebase. When we needed to connect different parts of the system, every question about data access required a response from that developer. Responses were slow. The project stalled. We resolved it by writing the API specification ourselves and working to that spec, with the third-party developer implementing it on their side. It worked, but the delay and the friction were entirely avoidable with a defined API layer from the start. The film industry production management tool we worked on presented a different version of the same problem. We expected to integrate directly with existing platforms used for storing production documents. When we finally got access to those systems, they were far more locked down than anticipated. There was no API access available. We had to build an alternative approach, ingesting emails tied to specific roles within a production to process data indirectly. The challenge was making that feel largely invisible to users, since the entire value of the integration was supposed to be seamless data pulling, and the workaround added a step. Finding a method that felt natural without the direct connection was the hardest part of that project. ## Negotiating API Access With Established Platforms Some platforms have APIs but do not make them freely available. Access is granted selectively, based on commercial agreements, volume commitments, or approval processes. A new product with no track record will often find these doors closed, even if the API technically exists. On a toll management project, we had to explain to the client what establishing a formal data-sharing relationship with toll operators would actually involve. A brand-new product with no user base has very little leverage in that conversation. Established toll operators are not obliged to prioritise integration work for an unproven entrant. We made the case that launching first using a preloaded credit model made more sense, and that pursuing API integrations with operators was a better conversation once the platform had demonstrated real usage and credibility. The client accepted that staged approach, and it was the right call. This pattern repeats across industries. [A new fitness app does not get priority access](https://weareaffective.com/learning-centre/fitness-app-trends-2026-what-users-really-want-from-their-workout-apps) to a gym chain's booking system. A new wellness platform does not immediately get a commercial API arrangement with a supplements fulfilment partner. The platform wants to know the integration is worth their development and maintenance effort, and that means you need to demonstrate demand first. When a partnership API you are depending on requires a formal commercial agreement, build the product to function without it first. Treat the API integration as an enhancement once the product proves its volume, rather than a dependency from day one. ## How Third-Party API Choices Shape Your Architecture [Every public API you integrate shapes what your architecture](https://weareaffective.com/app-architecture-design-we-are-affective) can and cannot do. The constraints are commercial, structural, and temporal. When we integrated Stripe Connect on a project requiring delayed payouts to simulate escrow, we found that different account types impose different constraints. Express accounts require near-immediate payouts, which did not suit our use case. Moving to a more controlled account type gave us the payment behaviour we needed, but each step toward more control added integration complexity. The balance between achieving precise payment flow behaviour and retaining the benefits of Stripe's default handling is genuinely narrow, and finding it required understanding Stripe's model deeply before writing integration code. On the travel product, the client switched aggregators midway through development because the first aggregator's fees made the business model unworkable. Because the two services used fundamentally different API approaches, we had to go back to the drawing board and re-engineer significant portions of the integration. Later, the client added a third external service for specific booking types, requiring another round. Each change meant reviewing integration code, rewriting connection logic, and testing for edge cases. The cumulative cost was substantial, and it came directly from API choices that were made or changed without accounting for their architectural consequences. ## Security Implications of Each Approach Public APIs introduce attack surface that you do not fully control. Your API keys can be exposed, your rate limits can be exhausted by malicious actors, and the provider can change authentication requirements without warning. [Serverion](https://www.serverion.com/uncategorized/securing-apis-encrypting-sensitive-data-end-to-end/) report that 61% of organisations have accidentally exposed secrets such as API keys in public repositories, which gives a sense of how commonly the basics go wrong. Private APIs carry different risks. Because you build and maintain them, the security posture depends entirely on your own decisions. Without an API layer acting as a controlled intermediary, clients touch the data store directly, and every access rule has to be set and maintained manually. On the performance coaching survey app, skipping a traditional API meant the Firebase security rules had to be locked down with real care. There was no API to act as a gatekeeper, so the rules themselves had to be precise enough to prevent any possible exploitation of either the app or the web response page. The fitness social app we worked on presented a different kind of security question, one driven by user data rather than API architecture. The original design showed users' real-time locations on a map so people could find workout partners. Research showed that [a high proportion of users were going to be female](https://weareaffective.com/learning-centre/what-a-fitness-social-app-changed-when-it-realised-precise-location-was-the-wron), which made precise location sharing a significant safety concern. The feature was redesigned to show only a randomised location offset, with exact location only revealed after users had reviewed each other's profiles and chosen to share. That is a security decision that shaped core product design, not just API policy. ## Scalability and Long-Term Maintenance Costs A private API you own is an asset you maintain. As the product grows, the API has to grow with it, which means engineering time, versioning decisions, and ongoing upkeep. That cost is real and often underestimated in early planning. A public API you consume is a dependency you do not control. The provider can deprecate endpoints, change rate limits, introduce fees, or shut the service down entirely. Each of those events requires your team to respond, often urgently. The more deeply a public API is embedded in your product, the more disruptive any change to it becomes. There is no clean answer. The calculation depends on how central the functionality is, whether a suitable public API exists, what the provider's track record is, and what your own team's capacity is to maintain a private alternative. What the drinks industry trading platform and the travel product both illustrate is that skipping the question entirely, or deferring it until the architecture is set, tends to produce the worst outcomes. The decision gets made by default rather than by design, and it costs more to unwind later than it would have cost to get right at the start. ## Partner Trust and Commercial Relationships [API access is often a proxy for commercial trust](https://weareaffective.com/learning-centre/how-do-i-build-trust-with-users-when-theyre-making-such-big-decisions). When a platform gives you API access, they are allowing your product to sit inside their ecosystem and, in some cases, to represent their data to your users. That carries obligations in both directions. On the memory-sharing project, using Deezer's API in the way Deezer intended meant we were fully compliant without needing workarounds, and the relationship between the two products was clean. Users who wanted a full track were directed toward a Deezer subscription, which meant the integration served Deezer's interests as well as ours. That alignment is what makes API partnerships sustainable. The opposite situation is one where a product tries to access platform data in ways the platform has not sanctioned. The temptation is usually that the data is genuinely useful and the official route is unavailable. But the compliance risk tends to materialise at the worst moment, when the product has grown enough to attract attention. On the toll management project, the instinct was to find ways to access toll data without a formal agreement. The better path was to [build something the operators would eventually want to partner with](https://weareaffective.com/learning-centre/why-does-our-competitor-feel-more-trusted-even-when-our-product-is-better), then negotiate from a position of demonstrated value. ## Staging Your API Strategy as the Product Matures Most products do not need a fully defined API strategy on day one. What they need is [a plan for how that strategy will develop as the product moves through stages](https://weareaffective.com/learning-centre/when-does-building-an-app-in-house-make-more-sense-than-outsourcing), from proof of concept to MVP to commercial launch to scale. The Firebase approach on the survey app was right for a proof of concept precisely because it was not a production architecture. It kept the build lean, proved the concept, and deferred the cost of a proper API layer to a point where the product had validated its value. The toll management product staged its API integrations by starting with a preloaded credit model and planning to add operator API integrations once credibility was established. Both decisions were deliberate rather than accidental. The staging question applies to whether you expose your own API as well. A product that starts internal-only can later open a partner API to trusted third parties, and later still publish a public API if the ecosystem justifies it. Running that sequence in the wrong order, publishing a public API before the internal one is stable, creates obligations to external developers before you have the internal consistency to honour them. 1. Prove the concept without a formal API if speed is the priority and security rules can be locked down manually. 2. Define a private API before you build a second client type or bring in a second developer team. 3. Integrate public third-party APIs that are robust and commercially aligned before building equivalents yourself. 4. Negotiate partner API access once the product has demonstrable usage to bring to the table. 5. Consider a published public API only when the ecosystem benefit outweighs the maintenance obligation. ## Conclusion Public and private APIs are tools with different properties, and most real products use both. A private API connects your app to your own backend. A public API connects your product to a third party's infrastructure. The choice of which public APIs to use, and when to build private ones rather than consume public ones, shapes cost, security, scalability, and commercial relationships in ways that compound over the product's lifetime. The projects above show the same lesson from different angles. A private API built too late creates bottlenecks and rework. A public API chosen without reading the terms costs compliance problems and architectural rewrites. Skipping an API layer entirely trades short-term speed for long-term fragility. And negotiating access to a closed API before the product has credibility is a conversation that tends not to go well. Getting the API strategy right is a product decision with commercial, technical, and user-facing consequences, and it is worth understanding clearly before the architecture is locked. If you are working through these questions on a product you are building or inheriting, [let's talk through your API strategy](https://weareaffective.com/get-started). ## Frequently Asked Questions What is the difference between a public and a private API? A private API is one you build and control yourself, connecting internal parts of your product such as a mobile app, web dashboard, and admin panel to a shared data source. A public API is one offered by a third party, such as a payment processor or music catalogue, that gives your product access to external data or infrastructure for an integration fee. When should a product team choose a private API over a public one? A private API makes the most sense when you need full control over your data model, when security requirements are strict, or when no suitable public API exists for your use case. It is also the right choice when the interface itself represents a competitive advantage you would not want to expose. When does it make sense to use a public API instead of building your own? Public APIs are a strong choice when a third party already holds something your users want and replicating it would be impractical or unnecessary. Music catalogues, mapping data, payment rails, and identity verification are all examples of infrastructure that took enormous resources to build and are far more efficient to licence than to recreate. What happens if you do not define an API early in the build process? Without an API layer in place, different parts of your product tend to make direct calls to the database, which creates both a security problem and a maintenance burden over time. Retrofitting an API later once multiple clients are already built is significantly more costly and disruptive than defining even a minimal one at the start. Are there risks to relying on a public API for core product functionality? Yes. When your product depends on a third-party API, you are subject to that provider's pricing, terms, and availability, all of which can change without much notice. It is important to understand what those dependencies mean for your product before committing to them, particularly if the API underpins a critical user journey. Can a product use both public and private APIs at the same time? Absolutely, and most mature products do. A well-designed private API can sit at the core of your product while public APIs handle specific functions such as payments, mapping, or catalogue access. The two approaches are not mutually exclusive and are often most effective when used together. What security considerations come with skipping a private API layer? Without a controlled API layer acting as an intermediary, security rules must be managed directly at the database level, which becomes increasingly difficult as the product grows. Every new feature or client that accesses the database directly expands the surface area that needs to be scrutinised and maintained. Can public API integrations generate revenue as well as access data? Yes, in some cases a public API integration can open up secondary income streams alongside the core product. 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