The verdict in three sentences
A documented B2B REST API (authentication, rate limiting, versioning) costs 12,000 to 30,000 EUR in 2026. Add 5,000 to 10,000 EUR for a self-service developer portal with API keys and interactive docs. Plan for 8 to 14 weeks and 300 to 700 EUR/month maintenance: a public API is a product, not just an endpoint.
What the budget covers
A serious partner API is more than exposing a database. It bundles security, quotas, logging, versioning and documentation. Each layer protects your system and your partners' developer experience.
| Item | 2026 range (EUR) | Role |
|---|---|---|
| Design + OpenAPI specs | 2,000 - 4,000 | Clear interface contract |
| REST endpoints (10-20) | 8,000 - 18,000 | Functional core |
| OAuth 2.0 / API keys auth | 2,000 - 4,500 | Access security |
| Rate limiting + quotas | 1,500 - 3,000 | Load protection |
| Versioning + backward compat | 1,500 - 3,500 | Evolve without breaking |
| Developer portal | 5,000 - 10,000 | Self-service onboarding |
| Maintenance | 300 - 700 /mo | Security, quotas, support |
Security and maintenance: the underestimated line
Buyers focus on endpoints and forget that securing an exposed API is continuous. An auth flaw or an unthrottled endpoint can expose your whole database or blow up your infrastructure bill.
| Security level | What's covered | 2026 cost (EUR) |
|---|---|---|
| Basic | API keys, HTTPS, logs | Included in core |
| Standard B2B | OAuth 2.0, rate limiting, quotas | +3,500 - 7,500 |
| Hardened | Fine scopes, audit trail, WAF, alerts | +6,000 - 12,000 |
| Annual maintenance | Patches, key rotation, monitoring | 3,600 - 8,400 /yr |
An API without monitoring is latent debt: the first undetected partner outage costs far more than the supervision subscription (50-200 EUR/month).
Mini case study
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Karim, product director at a logistics software vendor in Nantes, wants to open an API to 12 partner carriers. Quote: 16 endpoints 14,000 EUR, OAuth + quotas 5,000 EUR, developer portal 7,000 EUR, i.e. 26,000 EUR over 12 weeks. Maintenance: 500 EUR/month.
Result: each partner self-integrates via the portal, versus 3 days of manual support before (~1,500 EUR per onboarding). Across 12 partners in year one, support savings ~18,000 EUR, plus a sales argument to sign new carriers.
FAQ
Why does an API cost more than a plain export? An export ships a file; an API guarantees security, uptime, quotas and versioning continuously. Those guarantees are 40-50% of the budget, hence the 12,000-30,000 EUR range.
Is a developer portal essential? From 5-6 partners, yes: it slashes onboarding time and cuts your support tickets. Budget 5,000 to 10,000 EUR; it pays back on avoided support cost.
How does versioning work? You expose v1, v2… to evolve the API without breaking existing integrations. Budgeting 1,500 to 3,500 EUR upfront avoids costly rewrites later.
How much is maintenance? Between 300 and 700 EUR/month depending on traffic and security level: patches, key rotation, quota monitoring and first-line partner support.
Timeline for a first version? A documented 10-15 endpoint API ships in 8 to 12 weeks; add 2 weeks for the developer portal. A 5-endpoint MVP can ship in 5-6 weeks.
Let's scope your project. Tell us the number of partners, the data to expose and target security level: we price API + portal with a maintenance plan. 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.
