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API Development & Integration
250+ projects · 5.0 on Google · 100% in Germany

API integration & interface development for SMEs: REST, GraphQL, ERP connectivity

For mid-sized companies: REST, events and legacy bridges—stable for production and audits – delivery and project ownership from Germany (Leer/East Frisia), named contacts, no offshore guesswork.

  • 250+ delivered projects
  • 5.0 stars on Google
  • 100% engineering in Germany

We build interfaces and APIs so ERP, CRM and apps exchange data reliably—with REST, GraphQL and documented contracts from workshop to operations.

Our API Services

REST and GraphQL APIs

Development of modern, scalable APIs for your applications.

  • RESTful API Design
  • GraphQL Schemas

Microservice Architectures

Design and implementation of scalable microservice solutions.

  • Service Decomposition
  • API Gateway

System Integration

Connection of ERP, CRM and other business systems.

  • ERP Integration
  • CRM Connection
Björn Groenewold, contact for API development and integration
Stable APIs need contracts and tests before production: OpenAPI, error codes, monitoring per route. Otherwise integration debt hits operations.
Björn GroenewoldManaging Director, Groenewold IT Solutions

30-minute intro call: API Integration

Book a 30-minute, no-obligation intro call about API Integration – straightforward next steps.

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API Integration: Connecting Systems for Seamless Data Flow

Why API integrations matter

Modern businesses run on interconnected systems. Many organizations still move data with manual entry or nightly CSV exports.

Well-designed API integrations remove those bottlenecks. They enable real-time, bidirectional data flow between CRM, ERP, e-commerce, and specialized tools.

Our ERP integration services focus on breaking silos between platforms such as Odoo, SAP or Microsoft Dynamics—consistent mappings, reconciliation rules, monitoring and alerting included. See also API development costs.

We architect integration layers that stay robust for enterprise workloads. They remain flexible as your technology landscape evolves—supported by system integration and automation where processes need orchestration.

Choosing the right integration pattern

Choosing the right pattern matters for long-term success. Point-to-point fits simple cases.

Complex environments often need event-driven designs with message queues. Queues decouple systems and handle traffic spikes.

We review data volumes, latency needs, and reliability targets. Then we recommend REST APIs, GraphQL, webhooks, or asynchronous messaging that match real operations.

Security by design

Security is paramount in API development. Interfaces can become attack surfaces.

Our APIs use OAuth 2.0 or API keys with proper scoping. We use TLS for data in transit. We validate inputs to block injection attacks.

For sensitive integrations we add IP allowlists, rate limiting, and audit logging. You can meet compliance goals without sacrificing developer experience or performance.

Reliability in production

Reliable integrations need more than code that passes tests once.

We add error handling with retries, dead letter queues for failed messages, and monitoring that alerts when data flow breaks.

We document APIs with OpenAPI so future teams can extend them without reverse engineering. That maturity separates production integrations from brittle scripts.

Björn Groenewold, contact for API development and integration
Integration is more than code: who owns master data and how conflicts resolve matters before every API call.
Björn GroenewoldManaging Director, Groenewold IT Solutions

API Architecture: More Than Just Endpoints

A strong API architecture goes beyond single endpoints. For the broader picture across services, data flows and target architectures we offer a dedicated software architecture consulting page.

An API Gateway centralizes routing, authentication, and rate limiting. It protects backends consistently.

CORS policies control which domains may call your API.

Load balancing spreads traffic across instances and supports uptime during spikes.

Real-Time Integration and Event-Driven Systems

Not every flow fits classic request-response.

WebSockets give bidirectional real-time channels. They suit dashboards, chat, or live feeds.

Webhooks push events as they happen. Receivers avoid constant polling.

For decoupled, highly available setups we use message queues. They buffer traffic and improve delivery during outages.

Data Formats and Interoperability

Integration success depends on the right data formats.

JSON is the common choice for modern APIs. It is light, readable, and widely supported.

GraphQL lets clients request only the fields they need. That cuts over-fetching and can speed mobile apps.

Middleware translates between formats so heterogeneous systems can talk. For legacy systems, that layer often turns proprietary formats into modern standards.

Blog & related channels

API and integration work connects web, mobile, ERP and custom software—these blog categories and the web/mobile service page follow the same commercial core as this overview.

Frequently Asked Questions

API Integration

Costs & Legacy

How much does a simple API integration cost?

Standard APIs around €3,000–8,000 excl. VAT; more complex integrations with mapping from €10,000–25,000 excl. VAT. We give a quote after a short briefing.

How much does custom API development cost?

Simple CRUD APIs from €8,000 excl. VAT; full business APIs with auth and docs from €15,000–40,000 excl. VAT.

Can you integrate legacy systems?

Yes, via database access, file exchange, RPA or middleware. Effort is higher than for modern APIs; we scope after a short assessment.

What about documentation and maintenance?

We deliver API documentation and can run monitoring and support. When systems change, we update and test so integrations stay reliable.

Björn Groenewold – Geschäftsführer Groenewold IT Solutions

Discuss API integration

We give a quote after a short briefing.

Basics, architecture and standard integrations

REST or GraphQL – which is better for us?

REST is the standard and widely supported. GraphQL is better for complex, nested data structures and mobile apps. We advise based on your concrete use cases.

Can you connect to any system?

Usually yes. Many systems have APIs; for others we build adapters. Even with old legacy systems without interfaces we find solutions—via database access, file exchange or RPA.

Can you connect SAP and Salesforce?

Yes, that is a classic. We synchronise customer and order data bidirectionally. Also: SAP with shops, CRM systems with marketing automation, ERP with logistics.

Do you also develop APIs for apps and partners?

Yes, we design and develop APIs that other applications or partners can use—including documentation, authentication, rate limiting and versioning.

Björn Groenewold – Geschäftsführer Groenewold IT Solutions

Plan integration?

We analyse your system landscape and develop a clean integration architecture (Thorsten Frieling, project management).

Security, reliability and project timing

How do you secure the interfaces?

Through OAuth 2.0 or API keys for authentication, TLS encryption for transport and proper validation. For sensitive data additionally: encryption at rest, audit logging and IP whitelisting.

What happens if an interface fails?

We implement monitoring that reports errors early. Data is buffered and resent when the target system is available again. For critical processes: automatic fallbacks and alarm systems.

What does an interface development cost?

Strongly depends on complexity: simple standard integrations from €5,000, complex enterprise integrations with multiple systems correspondingly more. We start with a proof of concept if needed.

How long does an integration project take?

From a few days for standard APIs to months for complex enterprise landscapes. We usually start with a proof of concept to verify feasibility quickly.

Björn Groenewold – Geschäftsführer Groenewold IT Solutions

Questions about integrations?

We advise on architecture, security and cost—from experience with many enterprise projects (Björn Groenewold, CEO).

Scope: API integration vs system integration

This page is the main page for API and interface development (REST, GraphQL, ERP/CRM connectivity, OpenAPI, monitoring). Whole landscapes and process chains belong on system integration.

ERP, Microsoft 365 and headless CMS have dedicated entry points (ERP implementation, Microsoft 365 consulting, CMS development). Overview: integration & interfaces.

Related paths and adjacent topics

Service overview: Integration & interfaces (overview)

More integration & interface services

Adjacent service categories

API integration: from business cut to observability

Björn Groenewold

Up to 50% of your investment via BAFA/KfW

Use our funding calculator to see which government grants may apply to your project.

Björn GroenewoldManaging Director

Service cluster

Related services for Integration & interfaces: overview

Interfaces connect systems—together with integration and modernization you get a coherent IT landscape.

Related topics

Complementary services from other areas

These services are frequently requested together with API & Interface Development or complement it thematically.

Software & platforms: service overview

API Integration & Interface Development | Groenewold IT Solutions