Custom API Development
StepTo designs and builds secure, scalable APIs for the business logic your product depends on — whether the consumer is a web app, a mobile client, an IoT device, or a partner system. Our nearshore engineering teams in Belgrade, Serbia work in your timezone (CET) and ship production-grade APIs at 40-60% below typical Western European and US agency rates. From a first MVP endpoint to a globally-distributed microservices platform, we build APIs that are documented, observable, and genuinely pleasant to integrate with.
What We Build
- REST, GraphQL & gRPC APIs — the right protocol for each consumer, with clean resource modelling, pagination, filtering, and predictable error contracts.
- API gateways & edge — routing, authentication, rate limiting, caching, and request shaping with tools like Kong, AWS API Gateway, or Apigee.
- Microservices architecture — service decomposition, async messaging (Kafka, RabbitMQ, SQS), and event-driven patterns that scale with your traffic.
- Third-party & legacy integrations — payments, CRMs, ERPs, and SOAP/legacy systems, wrapped in resilient, idempotent integration layers.
- Documentation & SDKs — OpenAPI/GraphQL schemas, interactive docs, and client SDKs that make adoption fast for your team and partners.
How We Deliver
- API strategy & specification — we model resources and contracts first (design-first), so consumers can build against a stable schema early.
- Implementation in two-week sprints — incremental, testable endpoints with contract and integration tests from the start.
- Security & hardening — OWASP API Security Top 10, auth, rate limiting, and penetration testing before launch.
- Observability — structured logging, metrics, tracing, and alerting so you can see latency, errors, and usage in production.
- Lifecycle management — versioning, deprecation, and ongoing evolution as your product grows.
Why StepTo
- Senior backend engineers who have shipped APIs across fintech, healthcare, e-commerce, and logistics.
- CET-timezone collaboration — real-time design reviews and standups, not async-only handoffs.
- 40-60% cost savings versus Western European and US agencies at equivalent seniority.
- Security-first delivery aligned with OWASP and GDPR from day one.
- Full IP ownership and documented, handover-ready codebases.
FAQ: API Development
- Should I build a REST, GraphQL, or gRPC API?
- It depends on your consumers and traffic patterns. REST remains the best default for public APIs and broad client compatibility. GraphQL shines when clients (especially mobile or rich front-ends) need to fetch deeply nested data in a single round trip and you want to avoid over- and under-fetching. gRPC is the right choice for high-throughput internal service-to-service communication where latency and payload size matter. We often combine them — a REST or GraphQL edge for clients and gRPC between internal services — and recommend the mix based on your actual consumers rather than a default.
- How do you secure the APIs you build?
- We follow the OWASP API Security Top 10 throughout. That means authentication via OAuth 2.0 / OpenID Connect or signed JWTs, fine-grained authorization checks on every endpoint (not just at the gateway), input validation and schema enforcement, rate limiting and quota controls to prevent abuse, secrets management, and audit logging. For regulated workloads we add encryption in transit and at rest, PII handling aligned with GDPR, and penetration testing before launch.
- Can you integrate with third-party systems like payments, CRMs, and ERPs?
- Yes. Third-party integration is one of the most common reasons clients engage us — Stripe and other payment processors, Salesforce and HubSpot CRMs, NetSuite and SAP ERPs, messaging providers, and legacy SOAP services. We build resilient integrations with retries, idempotency keys, webhook handling, and circuit breakers so a flaky upstream provider does not take your product down.
- How do you handle API versioning and breaking changes?
- We design for evolution from day one. Public APIs get explicit versioning (URI or header-based), deprecation timelines, and backward-compatible changes wherever possible. For GraphQL we use schema deprecation rather than versioning. Every change is covered by contract tests so we catch breaking changes before they reach consumers.
- Do you provide documentation and developer onboarding?
- Always. We deliver machine-readable specs (OpenAPI/Swagger for REST, SDL for GraphQL), interactive documentation, example requests, and Postman or client SDK collections. Good documentation is part of the deliverable, not an afterthought — it is what makes an API actually adoptable by your team and partners.
- How much does custom API development cost with StepTo?
- Because our engineers are based in Serbia, blended rates run 40-60% below comparable Western European and US agencies for the same seniority. A focused API project typically runs from $20,000 for a well-scoped service to six figures for a full microservices platform with gateway, observability, and integrations. Most clients engage us as a dedicated team from $15K-25K/month for three engineers. See our pricing page for current bands.