How does API & integration development differ from Custom Business Apps?

This page covers the layer between existing systems: APIs, connectors, webhooks, middleware, and data synchronization. We do not build a complete application from scratch, we connect what is already there. If you need a whole application - dashboard, portal, or line-of-business system - Custom Business Apps is the right service. Often we combine both: a new application plus integration into your existing systems.

Which standards and protocols do you use?

For synchronous APIs we use REST, GraphQL, or gRPC depending on the requirement and document with OpenAPI. For event-driven integration we use webhooks and message brokers such as Apache Kafka, RabbitMQ, or MQTT. For legacy systems we work with SOAP, EDI formats (EDIFACT, X12), and file-based exchange. The choice follows latency, data volume, and your systems interfaces, not fashion.

Can you connect our ERP or CRM?

Yes. We have built connectors to SAP, Microsoft Dynamics, Odoo, Salesforce, and other systems. We use the vendor documented API or official integration layer instead of fragile direct database access. That keeps the connection stable even after updates to the ERP or CRM system.

How do you secure the interfaces?

Authentication via OAuth2 and OpenID Connect, API keys, or mTLS depending on context. On top of that come rate limiting, input validation, scopes for fine-grained permissions, and complete audit logging. For identity and authorization topics we use the same building blocks as on our member and tenant platforms, so auth stays central and traceable.

How are the integrations operated and monitored?

Every integration gets monitoring, alerting, and traceable logging. Failed messages land in a dead-letter queue and can be replayed in a controlled way instead of silently getting lost. We operate the integration on European infrastructure as a managed service - or hand it over to your team with runbooks.

What does an integration cost and how do projects run?

We start with an analysis of your system landscape and define the interface contracts. On that basis, after a scoping sprint with a defined scope you receive a binding fixed-price offer per integration or a package for several interfaces. We deliver in iterative releases - the first production-ready interfaces are typically available within a few weeks. We agree the concrete scope individually with you.

API & Integration Development

We build and connect interfaces between your existing systems: ERP, CRM, shop, legacy, and SaaS tools - via REST, GraphQL, gRPC, webhooks, message brokers, and change data capture. Secure, documented, and operated on European infrastructure.

REST · GraphQL · gRPC
Webhooks
Kafka · RabbitMQ · MQTT
OpenAPI

Book an intro call View building blocks

Reviews

Integration flowERP ↔ ShopExample

OrdersWebhook → ERP
Stocknear real time
Monitoringalerting active

IT Beratung Service Consulting Soforthilfe

Companies worldwide trust WZ-IT

Read client reviews

Integration, not silos

Your systems are fine - they just do not talk to each other

In most companies the actual software already exists: ERP, CRM, shop, accounting, industry solutions. What is missing are reliable interfaces between them. Manual transfer, nightly CSV exports, and brittle point-to-point scripts cost time and create exactly the inconsistencies that get expensive later.

Nightly CSV exports no one maintains anymore
Staff re-keying data between two systems
Point-to-point scripts that break on every update
Direct access to foreign databases instead of clean APIs
An expensive iPaaS license no one on the team understands

What we deliver

Six building blocks for robust integrations

We build the integration layer: APIs, connectors, webhooks, and middleware that connect your systems cleanly and traceably. The result is a data flow you can understand, monitor, and extend - without dependence on an opaque iPaaS black box.

APIs

API design & development
Clean, versioned interfaces built on REST, GraphQL, or gRPC - documented with OpenAPI, with explicit contracts between systems. We design the API along your domain, not as a mirror of a database table.

Systems

ERP & CRM connectivity
Connectivity to SAP, Microsoft Dynamics, Odoo, Salesforce, and other business systems. We know the typical pitfalls - tenants, document flows, master data - and address each native API cleanly instead of building fragile direct database access.
EDI & legacy interfaces
SOAP-to-REST wrappers, EDI formats (EDIFACT, X12), CSV, XML, and fixed-width files over SFTP or file share. We wrap legacy systems behind modern, well-testable interfaces without touching the legacy system itself.

Events

Webhooks & event-driven integration
Instead of polling systems every minute, they react to events: a new order, a status change, a payment immediately triggers the right follow-up step. With retry logic, idempotency, and dead-letter handling so no event gets lost.
Middleware & message brokers
A decoupling layer between your systems with Apache Kafka, RabbitMQ, or MQTT. Producers and consumers do not need to know each other, load spikes are buffered, and new consumers are added without rebuilding what already exists.

Data

Data synchronization & CDC
Keep systems consistent - via scheduled synchronization or change data capture that propagates changes in near real time. We define the system of record, resolve conflicts deterministically, and make the data flow traceable.

From a single API to event-driven middleware - we choose the right architecture per use case instead of solving every problem with the same pattern.

Use cases

Typical integration projects

Anywhere two or more systems need to work together reliably, a cleanly built interface pays off over a workaround.

Connect ERP to shop or portal
Articles, prices, stock levels, and orders flow automatically between ERP and online shop or customer portal. Orders land in the ERP without a media break, status changes flow back to the customer - without manual re-keying.
Provide a public or partner API
You want to give partners, integrators, or your own apps controlled access. We build a documented, secured API with authentication, rate limiting, and versioning - including a developer portal and OpenAPI specification.
Legacy SOAP to REST or webhook
An aging SOAP service needs to be consumed by modern applications. We put a REST or webhook facade in front, translate formats and error codes, and decouple new systems from the old protocol.
Workflow automation between SaaS tools
CRM, accounting, ticketing, and communication tools need to work together. For standardizable flows we use self-hosted n8n, for business-critical integrations we use custom code - or a combination of both.

Related services:

Auth & OIDC (member/tenant platforms)LLM tool & function calls workflow automation with n8n

Process

From system landscape to running integration

01
Analysis & contract
We map your systems, data objects, and triggers and define the interface contracts - including system of record, error behavior, and security model. Output: an OpenAPI or event specification everyone works against.
02
Build & test
Implementation in iterative releases against test and staging systems, with automated tests, idempotency, and replayability. The first production-ready interfaces are typically available within a few weeks.
03
Operations & monitoring
We operate the integration with monitoring, alerting, and traceable logging - or hand it over to your team with runbooks. Failed messages land in a dead-letter queue and are not lost.

Scoping Sprint

Define scope and price before development

Requirements, target architecture and effort are clarified. The result is a fixed-price offer for implementation.

Scoping Sprintfrom €1,490 excl. VATone-time

Book an intro call Explore the Scoping Sprint

Frequently Asked Questions

Answers to the most important questions

Beyond the interface

Need the whole application or a data platform?

Integration is often just one building block. When the task is bigger, we cover the rest with adjacent services.

Custom Business Apps

When it is not just the connection that is missing but a complete application is needed - dashboards, portals, line-of-business systems - we build it from the ground up.

To application development

Data Platforms

When it is about large data volumes, pipelines, CDC, and analytics, the data platform is the right place - integration and data synchronization mesh here.

To data platforms

Knowledge

Software projects with reliable outcomes

Proof for modernization, API extension, architecture, deployment and ongoing operations.

WZ-IT moved our studio infrastructure from decentralised individual devices to a central platform: every site is securely connected via VPN, new devices are onboarded automatically and an entire site is provisioned from a template, without manual steps on location. What impressed me most is the breadth and depth of their knowledge: Timo and Robin are not a typical IT provider who sets up a server and leaves. The two of them think their way into highly complex infrastructure and software topics, work through every requirement we put in front of them, and build networking, provisioning and operations so that everything fits together in the end. WZ-IT is an excellent partner for complex software, network and architecture projects.

Steve KirchnerManaging Director, nextGYM GmbH

View project

International

Built in Germany's Ruhr Valley. Running worldwide.

WZ-IT designs, develops and operates infrastructure and software for clients in Germany and internationally. We deliver projects remotely and continue supporting them in ongoing operations after go-live.