API development services are worth paying for because of the paths where things go wrong, and those are what the estimate actually covers.
What happens when the other end is down for an hour, returns a field that is not in the documentation, succeeds but takes ninety seconds, or receives the same order twice because somebody refreshed.
What API Development Services Have to Handle
Retries that do not make it worse. Backoff with a ceiling, and a limit after which it stops and tells somebody, so a brief outage at their end stays brief at yours.
Idempotency. The same request arriving twice creates one record. This is a design decision in the API contract, made at the start.
Dead letter handling. Messages that cannot be processed go somewhere a human can look at them, with enough context to understand why.
Alerting on the queue, not the request. The interesting signal is a growing backlog, which is visible long before any single call fails, and it is what gives you an hour to act rather than a phone call after the fact.
Where Integrations Actually Break
Rarely in the protocol. Almost always in the assumptions.
A field that is optional in the specification and mandatory in practice. A timestamp with no time zone, or an identifier that is unique per customer rather than globally.
Then a rate limit documented as one number and enforced as another, and a sandbox that behaves differently from production in exactly the way that matters.
We budget for discovering these, which is why the first phase is a small integration against the real system rather than a design document. It turns the estimate into a measurement.
What We Build
REST and JSON over HTTP, with OpenAPI specifications generated from the code rather than maintained alongside it and quietly diverging.
Webhooks with signature verification and replay protection. Scheduled synchronisation where webhooks are not offered, with a cursor so a missed run catches up rather than starting again.
Where the integration is with a named platform, the work is usually less about their API and more about their data model, so we read that first.
Integrating a Named Platform
Payment providers, shipping carriers, CRMs and accounting packages each have a documented API and an undocumented set of habits.
We keep a record of those habits per platform: which fields arrive empty rather than absent, which endpoints rate limit under load, and which webhooks fire twice. That record is what makes the second integration with the same platform cheaper than the first.
How the Work Runs
A test environment on both sides, then a small real integration, then the rest priced from what that revealed.
Our api development services hand over the specification, the retry configuration and the runbook for the dead letter queue, so your team can operate it. Tell us which two systems have to agree and what happens today when they do not.
Related Services
Where the integration moves data for analysis rather than driving a workflow, that is data engineering.
The application the API serves is web development. Where the API is the product, that is SaaS development.