Building your own technical gateway
Custom API development means your own software exposes data or actions to other software through a technical contract you own: which endpoints exist, who may access them, which input is valid and what a caller gets back on error. That differs from an API integration, where the technical gateways on both sides already exist.
A custom API is a technical gateway your own application offers so a website, app, internal system or external partner can read data or perform actions in a controlled way. Besides endpoints, that includes a contract for authentication, validation, error handling, documentation and future change.
Custom API, integration or something simpler?
Not every need for data exchange requires a new API. Who already offers the data and who needs it determines the smallest responsible form.
| Situation | Responsible first step | What must be clear first |
|---|---|---|
| Two existing systems with their own APIs must exchange data | Focused API integration between existing gateways | See the separate API integration page |
| Your software has no technical gateway yet and a web or mobile app must reach it safely | A custom API as part of that web or mobile app | Endpoints, data model, authentication and error handling |
| An external partner needs a limited, fixed selection of your business data | A bounded partner API with its own rights and limits | What is and is not visible, and who revokes access |
| Several of your apps — web, mobile, internal dashboard — must share the same data and rules | One underlying API those apps call together | Ownership of the data model and versioning across apps |
| One internal app uses the data directly and nobody else needs it | No separate API — direct access inside that application is enough | Reassess as soon as a second consumer appears |
€1,250 excl. VAT
An organisation with a non-standard process or product problem that first needs to investigate users, dependencies, risks and scope.
Independent project work that clarifies the problem, users, dependencies, risks and scope before an implementation price is provided.
Implementation not included
If an existing API already offers the needed data and rights, a small read test can verify that. If that contract is missing, you must develop it and agree it with the consumer. A successful call to an existing API is therefore not proof that a custom API is required.
The question usually appears when software you already have or are having built — a web app, mobile app or internal system — must expose data or actions to something else. Without an API that often happens through direct database access, a shared file or manual retyping: workable for one consumer, fragile once a second appears or the underlying data changes.
An API adds a fixed layer between data and consumers: who may read or change what, in which shape, and what happens on error. That is design work, not an automatic benefit. For one stable internal application without a second consumer, direct access is often still responsible.
A customer portal can call your backend API after login to return only orders, documents or status that customer may see. A mobile app can use the same API to read and sync when connectivity returns. An internal scanner can post a stock change that is validated before it is stored. An external partner can use a separate, limited API for exactly the agreed slice of your data.
These are illustrative patterns, not client cases or a list of supported platforms. Which form of custom API fits depends on existing software, the data model, users and the parties that will consume it.
One working call does not prove a usable API. A durable contract states which endpoints exist, which fields are required or optional, what a valid response is and what a caller sees on error. Without those agreements the first change breaks every consumer at once, without warning.
As more consumers appear — a second app, a partner, a new internal tool — that contract matters more than the first implementation. Versioning, backward compatibility and a planned deprecation path belong from the start, even with one consumer.
A custom API is a gateway your software offers. An API integration connects gateways that already exist on both sides. If both APIs already exist, start with integration.
No. Price depends on endpoints, data model, authentication, consumers and operations. OmniTechs first bounds one usable API route, then quotes separately.
No. It depends on the software you own or control, data quality, security constraints and who will operate the contract after delivery.
Bring which system must call what, who owns the data after delivery, and whether an API already exists on either side. That is enough for a free first assessment.
