The verdict in three sentences
Designing a public API for your platform costs between 20 000 and 55 000 EUR in Dublin in 2026, depending on the exposed surface and the level of self-service expected. It is not just a technical project: a public API is a product with its documentation, versioning and support, and it becomes an ecosystem revenue channel. Budget 6 to 12 weeks and a recurring maintenance cost, because breaking a public API breaks your partners' integrations.
The detailed quote
A public API is built in layers. Here are the 2026 ballpark figures for a platform in Dublin.
| Component | Content | Time | Cost (EUR) |
|---|---|---|---|
| REST or GraphQL design | Model, conventions, contracts | 5-8 d | 4 000 - 9 000 |
| Authentication (OAuth/keys) | Keys, scopes, rotation | 4-6 d | 3 000 - 7 000 |
| Quota / rate limiting | Plans, throttling | 3-5 d | 2 500 - 6 000 |
| Documentation (OpenAPI) | Reference, examples, SDK | 4-7 d | 3 000 - 7 500 |
| Versioning and deprecation | Strategy, backward compat | 3-5 d | 2 500 - 5 500 |
| Developer portal | Signup, keys, sandbox | 6-10 d | 5 000 - 12 000 |
| API monitoring and logs | Observability, live quotas | 3-5 d | 2 500 - 6 000 |
A "minimal but serious" API (design, auth, docs, quotas) costs 20 000-30 000 EUR; adding a full developer portal and advanced versioning pushes towards 55 000 EUR.
REST vs GraphQL: which to pick?
The paradigm choice affects the cost and the developer experience of your integrators.
| Criterion | REST | GraphQL |
|---|---|---|
| Design cost | 4 000 - 8 000 EUR | 5 000 - 10 000 EUR |
| Integrator learning curve | Low | Medium |
| Query flexibility | Limited | High |
| Native HTTP caching | Yes | Complex |
| Rate limiting | Simple | More complex |
| Auto documentation | OpenAPI | Introspectable schema |
REST remains the standard for a broad partner API; GraphQL shines when integrators have very varied data needs.
Key management, quotas and ecosystem revenue
A public API is monetised via tiered plans. Key and quota management is what makes that monetisation possible.
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| API plan | Quota / month | Rate limit | Indicative price (EUR) |
|---|---|---|---|
| Free / sandbox | 5 000 calls | 10 req/s | 0 |
| Starter | 100 000 calls | 30 req/s | 49 - 99 /mo |
| Business | 1 000 000 calls | 100 req/s | 199 - 499 /mo |
| Scale | 10 000 000 calls | 500 req/s | 900 - 2 500 /mo |
| Enterprise | Custom | Negotiated | On quote |
Even without billing the API directly, the integrator ecosystem raises your platform's retention and creates a network effect that is hard to copy.
Mini case study
Julien, CTO of a 30-person logistics SaaS platform in Dublin, wants to open a public API so carrier and software partners can connect in self-service. He picks REST design, OAuth, quotas, OpenAPI documentation and a developer portal for 38 000 EUR, with maintenance at 900 EUR/month. Previously each partner integration tied up a developer for ~5 days (about 3 000 EUR of internal cost) and Julien turned away half for lack of time. With self-service, 14 partners integrated on their own in the first year, saving ~42 000 EUR of custom dev and opening 3 new revenue-share deals.
FAQ
Is a developer portal needed from day one? Not necessarily. You can launch with OpenAPI documentation and manual key management (20 000-25 000 EUR), then add the self-service portal when integrator numbers justify it.
How do you change the API without breaking integrations? Through versioning: you keep the old version during a deprecation window (often 6 to 12 months) with a clear communication plan. It is a recurring cost to plan for.
Is a public API a security risk? It widens the attack surface, hence the importance of authentication, rate limiting and a dedicated security audit (see our audits from 6 000 EUR). It is manageable with good practices.
Can the API be monetised directly? Yes, via quota plans (see table). Even free, it creates value by locking in integrators and generating revenue-share deals.
How much is annual maintenance? Budget 10-20 % of the build cost per year, i.e. about 500 to 1 500 EUR/month to monitor, fix and evolve the API without breaking existing users.
Let's scope your project. Describe the surface to expose (objects, target partners), your preferred paradigm (REST/GraphQL) and your monetisation ambitions for a quote between 20 000 and 55 000 EUR. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
