The verdict in three sentences
Developing a complete public API in Amsterdam costs between EUR 25,000 and EUR 70,000 in 2026, developer portal, documentation and rate limiting included. The realistic timeline is 3 to 6 months and annual maintenance represents 10 to 15% of the project cost. A well-designed API becomes a distribution channel and a sales argument, not just a technical cost.
What a public API really contains
An internal API boils down to endpoints. A public API demands much more: robust authentication (OAuth 2.0, API keys), versioning, per-client quotas, interactive documentation, a self-service developer portal and monitoring. It is this "product" layer that explains the price gap.
| Component | Description | Budget weight |
|---|---|---|
| Core endpoints | CRUD + business logic | 30 - 40% |
| Authentication | OAuth 2.0, keys, scopes | 10 - 15% |
| Rate limiting & quotas | Protection, pricing plans | 10% |
| Developer portal | Docs, sandbox, onboarding | 15 - 20% |
| Documentation | OpenAPI/Swagger, examples | 10% |
| Monitoring & logs | Monitoring, alerts | 10% |
In the 2026 Amsterdam market, the day rate for a senior backend developer specialised in APIs sits between EUR 450 and 650. A standard project represents 60 to 110 person-days depending on the complexity of the data model and the level of security required.
REST or GraphQL, build or gateway: the 2026 trade-offs
Two decisions shape the budget: the paradigm (REST vs GraphQL) and the infrastructure (in-house build vs managed gateway such as AWS API Gateway, Kong, Apigee).
| Criterion | REST | GraphQL |
|---|---|---|
| Partner learning curve | Low | Medium |
| Data over-fetching | Frequent | None |
| Caching | Simple (HTTP) | Complex |
| Initial dev cost | EUR 25,000 - 55,000 | EUR 35,000 - 70,000 |
| Rate limiting | Standard | Per request/complexity |
| Ideal for | Broad public API | Mobile apps, rich data |
For infrastructure, a managed gateway (Kong, AWS API Gateway) costs EUR 50 to 500/month but cuts dev time by 15 to 25%. A fully in-house build offers total control but increases maintenance. For most publishers, REST + a managed gateway is the best cost/reliability ratio in 2026.
Mini case study
Thomas, CTO of a logistics SaaS publisher in Amsterdam (12 people), wanted to open an API to his 40 carrier partners to eliminate the case-by-case custom integrations. Each ad hoc integration cost him about EUR 4,500 and 3 weeks of development.
He invested EUR 52,000 in a REST public API with a self-service portal and sandbox. Result: partners integrate on their own in 2 to 4 days with no involvement from his team. Across 12 new partners in the first year, the saving is 12 x 4,500 = EUR 54,000, meaning payback in under 12 months, plus a decisive sales argument.
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FAQ
How much does a public API cost in 2026?
Between EUR 25,000 and 70,000 in Amsterdam, depending on data-model complexity, the paradigm (REST/GraphQL) and the level of the developer portal.
What timeline for a complete public API?
Expect 3 to 6 months, from API contract design to going live with the developer portal and interactive documentation.
REST or GraphQL for a partner API?
REST remains the standard for a broad, easy-to-adopt public API. GraphQL shines for mobile apps and rich data needs but costs 20 to 30% more.
Do I need a managed gateway?
A gateway (Kong, AWS API Gateway) costs EUR 50 to 500/month and cuts dev time by 15 to 25% while handling rate limiting and security. Recommended for most projects.
What annual maintenance budget?
Maintenance of 10 to 15% of the project cost per year, roughly EUR 3,000 to 10,000, for developer support, versioning and security updates.
Let's scope your project. Tell us your business objects, the number of target partners and your monetisation needs: we will price the right API and portal. 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.
