The verdict in three sentences
A custom API opens your data to partners in a controlled, documented and secure way. Budget 12,000 to 40,000 EUR (excl. tax) depending on the number of endpoints, the security level and availability commitments. Beyond development, plan for hosting (40 to 150 EUR/month) and 12%/year maintenance to hold a 99.9% SLA.
What it costs in 2026
API cost depends on the number of endpoints, the data model complexity and non-functional requirements (security, scaling, logging).
| API level | Timeline | 2026 cost (EUR excl. tax) | Hosting/month |
|---|---|---|---|
| Basic API (5-8 REST endpoints) | 5 weeks | 12,000 - 18,000 | 40 - 70 |
| Standard (OAuth + quotas) | 7 weeks | 18,000 - 27,000 | 60 - 100 |
| Advanced (GraphQL + webhooks) | 9 weeks | 27,000 - 35,000 | 90 - 130 |
| Platform (multi-tenant + SLA) | 10 weeks | 35,000 - 40,000+ | 120 - 150 |
2026 orders of magnitude, excluding heavy egress traffic and third-party licences (managed API gateway).
What really makes up the budget
Endpoint development is only part of the cost. Security, documentation and observability often account for 40 to 50% of the total.
| Item | Share of budget | Deliverable |
|---|---|---|
| Design + endpoints | 40 - 50% | Data model, REST/GraphQL routes |
| Security (OAuth, keys, quotas) | 15 - 20% | Authentication, rate limiting |
| OpenAPI documentation | 10 - 15% | Spec + developer portal |
| Tests + observability | 15 - 20% | Automated tests, logs, monitoring |
| Deployment + CI/CD | 5 - 10% | Pipeline, environments |
Mini case study
Sofia, CTO of a logistics scale-up in Lille, wants to expose her tracking data to 8 partners. Today each integration runs through manually exchanged CSV files, i.e. 1.5 days/month of developer work at 480 EUR/day, plus frequent disputes. A standard API at 24,000 EUR (excl. tax) removes these manual exchanges and enables partner self-service. Direct saving: about 720 EUR/month of developer time, on top of fewer disputes and faster partner onboarding (from 3 weeks to 3 days).
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FAQ
REST or GraphQL: which to choose?
REST remains the simplest standard to document and consume. GraphQL shines when partners have very varied data needs; it costs 15 to 25% more to design and secure.
How do you guarantee a 99.9% SLA?
That requires redundancy, monitoring, alerting and active maintenance. 99.9% allows about 43 minutes of downtime per month; holding it implies suitable hosting and on-call coverage.
Do you need a managed API gateway?
Useful once you expose to many partners: it handles quotas, keys and analytics. It adds a monthly cost but reduces custom security development.
Is documentation really necessary?
Yes, it is what makes the API adoptable. An OpenAPI spec and a developer portal sharply reduce support and speed up partner-side integration.
Let's scope your project. Describe the data to expose, the number of partners and your security and SLA requirements, and we will frame the API. 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.
