The verdict in three sentences
A production-grade public API is built for 25,000 to 70,000 EUR over 8 to 16 weeks, developer portal and documentation included. The classic mistake is thinking an API is just exposing internal endpoints: the value lies in robust authentication, rate limiting, webhooks and docs. Done right, a public API raises retention and unlocks partner deals otherwise impossible.
The cost per work package of a public API
A public API breaks into work packages, each with its own value. Here's the breakdown of a 48,000 EUR project.
| Work package | Scope | Effort (days) | Cost (2026 ballpark) |
|---|---|---|---|
| API design | Resources, versioning, conventions | 8 | 4,800 EUR |
| OAuth 2.0 authentication | API keys, scopes, tokens, rotation | 12 | 7,200 EUR |
| Rate limiting & quotas | Per plan, throttling, headers | 7 | 4,200 EUR |
| Core endpoints | Exposed business CRUD, pagination | 18 | 10,800 EUR |
| Webhooks | Events, signatures, retries, logs | 12 | 7,200 EUR |
| Documentation & SDK | OpenAPI, examples, JS/Python SDK | 10 | 6,000 EUR |
| Developer portal | Signup, keys, sandbox, logs | 12 | 7,200 EUR |
| Security & testing | Light pentest, load tests | 3 | 1,800 EUR |
| Total | ~10-14 weeks | 82 | ~49,200 EUR |
The developer portal and webhooks are often underestimated, yet they're what let a partner integrate your API autonomously without tying up your team.
REST vs GraphQL: which for a public API?
| Criterion | REST | GraphQL |
|---|---|---|
| Partner adoption curve | Low (universal) | Medium |
| Data over-fetching | Possible | Avoided |
| Setup cost | Lower | Higher (+15-25%) |
| Tooling & caching | Mature | Improving |
| Rate limiting | Simple (per endpoint) | Complex (per query cost) |
| Best for | Broad public API | Internal/mobile clients |
| Recommendation | Partner API | Targeted complement |
For a public API serving varied partners, REST remains the pragmatic choice: universal, easy to document and to limit. GraphQL shines internally or for mobile clients with precise data needs.
The business impact of an open API
| Lever | Without public API | With public API | Effect |
|---|---|---|---|
| Annual retention | ~82% | ~90% | +8 pts (integrations = switching cost) |
| Partner deals/yr | 2-3 | 8-12 | Multiplied distribution |
| Client time-to-integration | 3-6 weeks (custom) | 3-6 days (self-service) | Shorter sales cycle |
| Integration support cost | High (team involved) | Low (docs + sandbox) | Margin preserved |
A public API turns your SaaS into a platform: every integration creates a switching cost for the client and an entry point for new partners.
Mini case study
Need a professional website?
Kolonell builds websites that attract clients, optimized for the Sénégalese market. Free quote in 2 minutes.
Marc, CTO of a logistics-management SaaS in Lille (140 B2B clients), loses deals to competitors integrated with ERPs. He invests 48,000 EUR in a public API delivered in 12 weeks. Six months later: 9 partners have integrated the API, retention rises from 83% to 90%, and 4 large accounts sign solely because the connection to their ERP is native. On an ARPA of 5,000 EUR/yr, the 7 retention points gained across 140 clients represent ~49,000 EUR of preserved revenue per year: the API pays for itself in under a year, excluding new deals.
FAQ
How much does opening a public API cost in 2026?
Between 25,000 and 70,000 EUR depending on the number of endpoints, webhook support and the developer-portal scope. A solid base (OAuth, rate limiting, docs, sandbox) runs around 45,000-50,000 EUR.
Do I need a developer portal from the start?
Yes, even a minimal one: signup, key generation, documentation and sandbox. It's what lets partners self-integrate and keeps your technical team from drowning in support.
REST or GraphQL for external partners?
REST in most cases: universal, easy to document, version and rate-limit. GraphQL is justified mainly for your own mobile clients or very targeted data needs.
Are webhooks essential?
For true real-time integration, yes. Without webhooks, partners poll, which is costly and slow. Budget ~7,200 EUR for robust webhooks with signatures and retries.
How do I secure a public API?
OAuth 2.0 with scopes, token rotation, per-plan rate limiting, webhook signatures and audit logs. A light pentest before go-live is strongly recommended.
Let's scope your project. Tell us the endpoints to expose, your webhook needs and your indicative budget (25,000-70,000 EUR): we'll scope the API design and the developer portal. 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.
