The verdict in three sentences
A serious internal REST API costs 25,000 to 55,000 EUR depending on the number of endpoints, security and documentation level. The price of version one is only half the story: versioning and running the API over 2 years can double the bill if ignored at scoping. Budget 10 to 14 weeks for a documented, secured and monitored API ready for external partners.
The module-by-module cost breakdown
In Berlin, a mid-sized company wanting to expose its data (catalogue, customers, orders) to its own apps and to partners pays not just for code, but for security, documentation and long-term stability. Here is the 2026 order of magnitude.
| Module | 2026 range (EUR) | Contents |
|---|---|---|
| REST API (core, endpoints) | 15,000 - 40,000 | Modelling, CRUD endpoints, tests |
| OpenAPI / Swagger documentation | 2,500 | Specification, developer portal |
| Gateway + rate limiting | 4,000 | Quotas, throttling, API key |
| OAuth2 / JWT authentication | 3,000 | Scopes, tokens, refresh |
| Monitoring and logs | 3,000 | Traces, alerts, dashboard |
| Project total | 27,500 - 52,500 | Excluding hosting and running |
The API core varies mainly with the number of endpoints and business-rule complexity. An 8-endpoint API is nothing like a 40-endpoint API with pagination, filters and fine-grained permissions.
| Scope | Endpoints | API core (EUR) |
|---|---|---|
| Minimal API | 5 - 10 | 15,000 - 22,000 |
| Standard API | 10 - 20 | 22,000 - 32,000 |
| Rich API (filters, roles) | 20 - 40 | 32,000 - 40,000 |
| Partner API (SLA, multi-tenant) | 40+ | 40,000 - 55,000 |
Running cost and versioning over 2 years
An API is not a frozen deliverable: it lives, evolves and must stay backward-compatible so it does not break your partners' integrations. Here is what to provision beyond V1.
| Line over 2 years | Estimate (EUR) | Frequency |
|---|---|---|
| Hosting + gateway | 3,600 - 12,000 | 150 - 500 EUR/month |
| Corrective maintenance | 6,000 - 12,000 | 15-20% of project/year |
| Versioning (v2, deprecation) | 5,000 - 10,000 | 1 major version |
| Partner support | 3,000 - 8,000 | Depending on SLA |
| 2-year total | 17,600 - 42,000 | On top of V1 |
The lesson: budget the API over 2 years, not on the initial development cost alone. A 35,000 EUR API can cost 60,000 to 70,000 EUR over 24 months all-in.
Mini case study
Camille, CIO of a mid-sized food-trading company in Berlin, wants to expose her catalogue and stock to 12 distribution partners who until now integrated prices via Excel files sent weekly. That process consumed 1.5 person-days a week and produced price discrepancies at partners.
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She commissions a standard REST API (16 endpoints) at 34,000 EUR, delivered in 12 weeks, with OAuth2 and rate limiting. The 1.5 weekly days vanish (about 78 person-days saved per year, roughly 23,000 EUR) and partner price discrepancies drop to zero since they read the single source. Estimated V1 payback in 20 months, running costs included.
FAQ
Why does an internal API cost more than a simple data export?
Because you pay for security (OAuth2, rate limiting), documentation and long-term stability. A one-off export costs 2,000 to 5,000 EUR; a living API used by partners requires 25,000 EUR and up.
Do we really need a gateway and rate limiting?
As soon as third parties call the API, yes. The gateway (around 4,000 EUR) protects against abuse, caps quotas per key and prevents a badly coded partner from saturating your infrastructure.
How much does it cost to host an API in production?
From 150 to 500 EUR/month depending on traffic and the chosen gateway, i.e. 3,600 to 12,000 EUR over 2 years. A high-traffic or multi-region API costs more.
How do we evolve the API without breaking integrations?
Through versioning: you publish a v2 while keeping v1 running during an announced deprecation window (often 6 to 12 months). Budget 5,000 to 10,000 EUR for a major version over 2 years.
What is the timeline for a usable first version?
10 to 14 weeks for a documented, secured standard API: 2 to 3 weeks of design, 5 to 7 of development, 2 to 3 of testing, documentation and go-live.
Let's scope your project. Tell us the data to expose, the estimated number of endpoints and who consumes the API (internal apps, partners): we scope the perimeter and a budget between 25,000 and 55,000 EUR, running costs included. 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.
