The verdict in three sentences
A custom API opens your platform to partner integrations and prepares for scale: expect 25,000 to 90,000 EUR (excl. tax) in 2026 with a gateway, versioning and OpenAPI documentation. Microservices are not a goal in themselves: they add 20 to 40 % operating overhead and only make sense beyond a certain load with a large enough team. For 80 % of projects, a well-designed modular monolith is faster, cheaper and perfectly scalable.
What a custom API covers
A professional API is more than exposing data. It includes security, versioning, quotas and documentation. Here are the 2026 items.
| Component | Role | 2026 range (EUR excl. tax) |
|---|---|---|
| Design and data model | Contracts, resources, consistency | 5,000 - 15,000 |
| API gateway | Routing, quotas, API keys | 6,000 - 18,000 |
| Authentication / OAuth2 | Security, scopes, tokens | 5,000 - 14,000 |
| Versioning | Backward compatibility | 3,000 - 9,000 |
| OpenAPI documentation | Developer portal, examples | 4,000 - 12,000 |
| Monitoring and logs | Observability, alerts | 5,000 - 15,000 |
| Testing and load | Reliability, scaling | 4,000 - 12,000 |
A simple internal API stays under 35,000 EUR; a public partner API with developer portal, quotas and SLA exceeds 70,000 EUR.
Modular monolith or microservices?
The most poorly settled question of 2026. Microservices solve scale and organizational problems, not code problems. Here is the decision grid.
| Criterion | Modular monolith | Microservices |
|---|---|---|
| Initial build cost | Baseline | +15 to 30 % |
| Operating overhead | Baseline | +20 to 40 %/yr |
| Suitable team size | 2 to 8 devs | 3+ autonomous teams |
| Load / traffic | Up to very high | Extreme, isolated peaks |
| Deployment | Simple, unified | Independent per service |
| Operational complexity | Low | High (orchestration) |
| Time to value | Short | Long |
2026 rule: start with a modular monolith (clear module boundaries). Only split into microservices the module that poses a real load or team problem. Premature splitting is the number one cause of budget overrun.
When NOT to use microservices
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- Team of fewer than 3 developers: orchestration cost outweighs the benefit.
- Predictable, moderate traffic: a well-optimized monolith handles millions of requests/day.
- Critical time-to-market: microservices slow the start.
- No mature container platform: operations become a money pit.
Mini case study
Sofiane, CTO of a 30-person B2B SaaS scale-up in Paris, is considering moving his platform to microservices to reassure a future integration partner. His load: 1.2 million requests/day, served by a monolith on 3 servers.
Full microservices quote: ~85,000 EUR to build + +30 % operations, i.e. +22,000 EUR/year in infrastructure and ops time. Chosen alternative: a custom API (48,000 EUR) exposed through a gateway on the existing monolith. Result: partner integrations open in 3 months with no operating overhead, and the microservices split is deferred to the real threshold of 5 to 10 million requests/day. Immediate saving: ~59,000 EUR.
FAQ
How much does a custom API cost in 2026? Between 25,000 and 90,000 EUR (excl. tax). A simple internal API stays under 35,000 EUR, while a public partner API with portal and SLA exceeds 70,000 EUR.
Do I need microservices to scale? No. A well-designed modular monolith absorbs very high loads. Microservices add 20 to 40 % operating overhead and only pay off at very large scale or with several autonomous teams.
What does an API gateway bring? It centralizes routing, authentication, quotas and monitoring. Expect 6,000 to 18,000 EUR; it is the essential control point once you open the API to third parties.
Why document with OpenAPI? Because the documentation becomes a portal your partners can use, with examples and tests. This item (4,000-12,000 EUR) dramatically reduces integration time on the client side.
How long to deliver an API? From 3 to 7 months depending on functional surface and security requirements. A first usable partner version can ship in 8 to 12 weeks.
Let's scope your project. Describe your current platform, your load and your partner integration needs: we settle modular monolith vs microservices and cost 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.
