The verdict in three sentences
A professional REST API delivered with OpenAPI documentation, OAuth2 authentication, rate limiting, and versioning costs 15,000 to 45,000 EUR depending on the number of endpoints and business complexity. The realistic timeline is 6 to 12 weeks, including tests and developer documentation. GraphQL can reduce over-fetching for rich clients, but REST remains the default choice for simplicity and caching.
What the budget covers
The price is not limited to endpoint code: security, documentation, and observability often account for 40% of the effort.
| API scope | Cost (EUR) | Security included | Annual maintenance |
|---|---|---|---|
| Internal API (5-10 endpoints) | 15,000 - 22,000 | API key + HTTPS | 2,500 - 4,000 EUR |
| Partner API (10-20 endpoints) | 22,000 - 35,000 | OAuth2 + rate limiting | 4,000 - 6,500 EUR |
| Public API (20+ endpoints) | 35,000 - 45,000+ | OAuth2 + quotas + versioning | 6,500 - 9,000 EUR |
| OpenAPI docs + portal | 3,000 - 8,000 | — | included |
| Developer sandbox | 4,000 - 9,000 | Test keys | included |
REST or GraphQL: which to choose
The protocol affects client development cost and server load. Here are the 2026 ballpark figures.
| Criterion | REST | GraphQL |
|---|---|---|
| Initial build cost | 15,000 - 45,000 EUR | 20,000 - 55,000 EUR |
| Native HTTP caching | Excellent | Complex |
| Data over-fetching | Frequent | Eliminated |
| Team learning curve | Low | Medium to high |
| Best for | Partners, integrations | Rich mobile/SPA apps |
| Monitoring | Standard | Specific tooling |
Mini case study
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Thomas, CTO of a logistics scale-up in Berlin, wants to open a partner API so 12 carriers can pull delivery statuses in real time. He chooses a 16-endpoint REST API at 31,000 EUR, with OAuth2, rate limiting at 600 req/min, and an OpenAPI portal. Hosting + monitoring costs 180 EUR/month. Each partner integrating autonomously avoids 2 days of manual onboarding support (about 900 EUR): across 12 carriers, the API saves 10,800 EUR of support in the first year, on top of opening a new commercial channel.
FAQ
Why document with OpenAPI? An OpenAPI contract lets partners auto-generate their client and cuts support tickets by 50 to 70%. The documentation portal costs 3,000 to 8,000 EUR but pays off from the first integrations.
How much does API hosting cost? For SME traffic, budget 80 to 300 EUR/month (server, database, monitoring), plus a CDN if you serve media.
Should I version from the start? Yes: versioning (v1, v2) costs a few build days but avoids breaking partner integrations during upgrades, protecting your B2B revenue.
What timeline for a partner API? Between 6 and 12 weeks depending on endpoint count, with 2 to 3 weeks dedicated to security and load testing.
REST or GraphQL for partners? REST is still recommended: native caching, integration simplicity, and universal tooling. GraphQL is mainly justified for rich front-end apps consuming your data.
Let's scope your project. State the number of endpoints, target consumers (internal, partners, public), and security level for a quote between 15,000 and 45,000 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.
