API Integration and Custom Software Development

What the Service Covers

Custom software development, API design and system integrations are handled together, according to what the project needs. Every project needs something different, so the scope is shaped around the areas that are actually required, without adding unnecessary technical weight.

• Custom Software Development

  We build custom software for business rules, approval flows, calculation processes or operational needs that off-the-shelf software does not cover. Depending on the situation, rather than replacing systems entirely, we design solutions that can add the functions needed on top of the existing structure.

• REST API Design

  We design REST APIs together with their resource and endpoint structure, authentication, authorisation, error handling, pagination and rate limits. For APIs that will be opened to external systems, the contract and the data model are settled before development starts.

• System Integrations

  We connect ERP, CRM, payment, shipping, marketplace and other business systems to each other. The direction of the data flow, the source of truth, the field mappings and what happens in error cases are established before the integration is built.

• Data Migration

  When moving data from old systems into new structures, we clean it, map it and check it before the transfer. A rehearsal migration is run before going live, and a rollback plan is prepared for data loss or incorrect matching.

• Process Automation

  We automate repeated operations with scheduled jobs and event-triggered flows. Webhook-based processes carry data between systems, and notification and error handling mechanisms come into play when something unexpected happens.

• Documentation and Versioning

  We document OpenAPI definitions, example requests and responses, authentication methods and versioning rules. Changes that could affect an application are planned in advance, and where necessary old API versions run alongside the new one for a defined period.

When Is Custom Software Needed?

Custom software is not the right answer for every business. If a ready-made product meets the need, we look at that first. The need for custom software usually appears where existing tools do not cover the business processes, or where manual steps between systems have become critical:

• The same data being entered by hand into more than one system
• Business rules or approval flows that off-the-shelf software cannot cover
• Data moving between systems through Excel or CSV files
• An API requirement from a partner, a marketplace or a corporate customer
• Different systems producing different results for the same operation, and the manual reconciliation this creates

Systems We Connect

The scope of an integration is not set by the software we build alone. The other system's API structure, quota policy, test environment, access model and versioning policy are all significant parts of the technical scope.

• ERP and bookkeeping software
• Private integrators for e-invoicing and e-archive invoicing
• Payment institutions and virtual POS systems
• Shipping and logistics services
• Marketplaces and product management systems
• CRM and marketing automation platforms
• Email and SMS delivery services
• OAuth 2.0 and single sign-on systems
• Database or file-based middle layers for legacy systems that have no API

How We Work

1. Discovery and Data Map

   We establish where each piece of data is created, which system is the source of truth and which way the data flows. Field mappings, data flows and error scenarios are documented system by system.

2. API Contract and Design

   Endpoints, data fields, the authorisation model and error formats are settled through an OpenAPI definition. Producing the API contract before development makes the technical scope visible from the start.

3. Development and Testing

   Development runs in separate test environments with controlled data. Timeouts, duplicate records, half-finished operations, unexpected responses and the other system being unreachable are each tested separately.

4. Going Live

   The integration is switched on in a controlled way, with a phased rollout and a rollback plan where needed. In the first days we watch the data flow and the error logs closely to confirm how the system behaves.

5. Monitoring and Versioning

   We monitor API response times, error rates and data flows. Version changes in the other systems are followed, and the technical adjustments and development they call for are planned.

What Is Delivered

• OpenAPI Definition

  We produce browsable documentation covering API endpoints, data fields, parameters and example requests and responses. It gives any developer a source they can use to understand the integration independently.

• Authentication and Permissions

  We set up authentication based on API keys, tokens or OAuth. Which user or role can reach which data is defined explicitly within the technical documentation.

• Error Dictionary

  We document the error codes the API can return and what should be done in response to each of them. Errors that can be retried are identified separately, which makes error handling more predictable.

• Limits and Versioning Policy

  We set the rate limits, the quota rules and what happens when they are exceeded. How API changes that could affect an application will be announced, and how long old versions stay supported, are defined from the start.

• Logs and Error Alerts

  The state of the integrations is followed through logs and error records. When a data flow stops or an error occurs, the relevant alerting mechanisms come into play.

• Source Code and Access

  Source code, repository access, the deployment structure, environment variables and the third-party access details needed are delivered according to the scope of the project. Handover and access terms are defined explicitly in the contract.