The verdict in three sentences
Exposing a partner API to 40 integrators takes a budget of 27,000 to 65,000 USD (25,000 to 60,000 EUR) and about 3 months, a third of which goes to security and documentation rather than the endpoints themselves. The trio of OAuth 2.0, rate limiting and OpenAPI documentation is non-negotiable: without it, every partner becomes a support ticket and a leak risk. A managed API gateway at 330 to 1,600 USD a month costs less than rebuilding keys, quotas and logging in-house.
The detailed budget for a partner API
The CTO of a New York scale-up (logistics, HR or B2B fintech) needs to open the platform to software vendors and integrators. Here is the 2026 breakdown seen for a REST API with 25 to 40 endpoints.
| Work package | Content | 2026 budget | Person-days |
|---|---|---|---|
| Scoping and API design | Resources, versioning, conventions, OpenAPI 3.1 contract | 4,300 to 7,600 USD | 6 to 10 |
| Authentication | OAuth 2.0 client credentials, per-partner scopes, secret rotation | 5,400 to 10,800 USD | 8 to 14 |
| Endpoints and webhooks | Read, write, HMAC-signed events | 8,700 to 21,700 USD | 12 to 30 |
| Quotas and rate limiting | Per-partner plans, quota headers, 429 responses | 2,200 to 5,400 USD | 3 to 7 |
| Developer portal | Interactive docs, sandbox, key management | 4,300 to 13,000 USD | 6 to 18 |
| Testing and security | Contract tests, OWASP API Top 10 penetration test | 2,200 to 6,500 USD | 3 to 8 |
Total: 27,000 USD for a tight scope with an open-source portal, up to 65,000 USD with full webhooks, an isolated sandbox and an external pentest.
API gateway: buy or build?
The gateway handles keys, quotas, logging and usage analytics. Rebuilding it means 15 to 25 days of development plus maintenance.
| Solution | 2026 monthly cost | Strengths | Limits |
|---|---|---|---|
| AWS API Gateway | 330 to 650 USD for 50 M calls | Pay-as-you-go, AWS integration | Basic developer portal |
| Kong Konnect | 540 to 1,600 USD | Rich plugins, hybrid | Learning curve |
| Azure API Management (Standard) | ≈ 760 USD | Portal included | High fixed cost to start |
| Self-hosted Tyk or Kong open source | 160 to 330 USD of infrastructure | Full control, hosting of your choice | You run operations |
| In-house build | 0 USD licence | Fully custom | 15 to 25 days, security risk |
For 40 partners and under 50 million calls a month, a managed gateway in a US East region is almost always the best cost and risk trade-off.
Security rules you should not negotiate
- One OAuth client per partner, with minimal scopes: a billing integrator has no business reading HR data.
- Short-lived tokens (15 to 60 minutes) and secret rotation every 90 days.
- Per-partner rate limiting, for example 100 requests per second at peak plus a daily quota.
- Signed, replayable webhooks, with timestamps to block replay attacks.
- Logs kept 12 months for customer audits and SOC 2, with no personal data in clear text.
- Explicit versioning (v1, v2) and a 6 to 12-month deprecation notice.
The most frequent flaw in the OWASP API Top 10 is still broken object level authorization (BOLA): a partner changes an ID in the URL and reads another customer's data. Automated tests from the first sprint prevent it.
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Mini case study
Camille, CTO of an HR SaaS scale-up in New York, receives 40 integration requests from payroll firms and software vendors. Today each custom integration takes 8 days of her team's time, 320 person-days at 650 USD: 208,000 USD of internal cost. She orders a partner API at 52,000 USD plus a gateway at 650 USD a month. With OpenAPI docs and a sandbox, an integration needs only 1.5 days of support: 60 days for the 40 partners, or 39,000 USD. First-year savings: 208,000 - 52,000 - 39,000 - 7,800 = 109,200 USD, before any revenue from paid integrations.
FAQ
REST or GraphQL for a partner API?
REST with OpenAPI remains the standard expected by 80% of B2B integrators in 2026. GraphQL makes sense for partners building rich screens, at the cost of quotas that are harder to compute.
Should API access be paid?
Many platforms offer a limited free plan (for example 10,000 calls a month) and paid plans from 200 to 2,000 USD a month. The gateway manages these plans with no extra development.
How much does API maintenance cost?
Plan for 15 to 20% of the initial budget per year, about 5,400 to 13,000 USD, for fixes, version upgrades and level-2 partner support.
Is a penetration test mandatory?
Not legally, but enterprise customers will ask for it. A targeted API pentest costs 4,300 to 9,800 USD for 3 to 5 days of audit.
Let's scope your project. Share the resources you want to expose and the number of target partners: we price API design, security, the developer portal and the gateway, with an indicative budget and a 3-month 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.
