API developer: what they do and when your company needs this profile

A mobile application queries business information, e-commerce needs to check inventory, the CRM exchanges data with other systems, and a partner requires access to certain operations. As these connections increase, communication between applications begins to become a critical part of the architecture.

APIs provide interfaces for those systems to exchange information and execute operations following defined rules. While the ecosystem is small, its development can be part of the usual responsibilities of Backend. When multiple consumers, external integrations, microservices, or APIs that are part of the product appear, maintaining those interfaces requires greater specialization.

This is where the API Developer becomes relevant: a Backend profile specialized in designing, developing, and maintaining the interfaces through which different systems communicate.

Their responsibility does not end when an endpoint returns the expected response. An enterprise API must remain secure, documented, observable, and sufficiently stable to evolve without breaking the applications that depend on it.

What an API developer does

An API Developer works on the layer that connects applications, services, and data sources. They can develop APIs used by a frontend, a mobile application, internal systems, microservices, partners, or external clients.

Within lateam, this specialization is directly related to Backend Developers, as it shares knowledge about business logic, databases, security, and system integration.

The difference appears in the level of concentration on the lifecycle of the interfaces.

An API Developer must think simultaneously about who produces the information and the systems that will consume it. This involves designing clear contracts, determining how consumers authenticate, controlling permissions, managing errors, documenting behaviors, and anticipating how the API will evolve.

When there are numerous consumers, a seemingly small decision can propagate throughout the technological ecosystem.

An API functions as a contract between systems

Suppose an API returns information about customers, and a mobile application uses a field called customer_id. Later, the Backend team modifies the structure and removes that field.

From the server's perspective, the change may seem simple. From the perspective of the application consuming the API, the contract has just been broken.

This type of dependency explains why designing APIs requires thinking beyond the current implementation.

A contract should define resources, available operations, request and response structures, data types, status codes, authentication, and possible errors. Tools and specifications like OpenAPI allow for structured descriptions of these elements and maintaining documentation associated with the interface.

Stability also depends on how changes are managed. Versioning, backward compatibility, and deprecation policies allow for introducing new capabilities without forcing all consumers to update immediately.

When APIs begin to connect different domains and services, these decisions become part of the Software Architecture of the product.

REST, GraphQL, and gRPC address different needs

An API Developer can work with different communication styles. The choice should depend on who consumes the interface, what type of information is exchanged, and what characteristics the architecture needs.

REST continues to be a common choice for web applications, mobile, enterprise integrations, and APIs intended for third parties. Its ecosystem, compatibility with HTTP, and ease of adoption allow for building understandable interfaces for a wide variety of consumers.

GraphQL introduces a model where the client can specify more precisely what information they need. It can be useful when different interfaces consume different combinations of data, although it also introduces its own considerations regarding caching, security, query complexity, and observability.

gRPC may be suitable for certain communication scenarios between services, especially when strict contracts and efficiency are priorities.

The same architecture can use more than one.

The experience of an API Developer allows for evaluating these alternatives without turning a specific technology into the default answer for all cases.

Enterprise integrations turn APIs into infrastructure

A company can start with a relatively simple architecture: frontend, backend, and database.

Then new needs arise.

The CRM needs to connect with marketing automation. The e-commerce needs to query an ERP. The mobile application uses services from the same backend. A payment provider sends events. Business Intelligence teams need certain data, and some partners request access to specific functionalities.

APIs then begin to act as an integration layer.

The API Developer needs to understand which system holds each piece of data, what operations can be exposed, how to avoid unnecessary dependencies, and what happens when one of the connected systems stops responding.

This last point is particularly important. An external integration introduces a dependency whose performance and availability are partially outside the company's control.

Timeouts, retries, circuit breakers, queues, and asynchronous processing can be part of the solution depending on the type of integration and the consequences of a failure.

The security of an API starts before publishing it

An API exposes operations and data through interfaces specifically designed to be used by other systems. This makes authentication, authorization, and access control structural responsibilities.

It is not enough to check that the consumer is logged in. The system needs to determine what operations they can execute and on which resources.

An API Developer can work with mechanisms like OAuth 2.0, tokens, and different permission models depending on the architecture. They must also correctly validate the information received and prevent error messages from revealing unnecessary internal details.

Among the controls that can be part of the design are:

• authentication and authorization based on the type of consumer;

• input and parameter validation;

• rate limiting and usage quotas;

• secure management of tokens, secrets, and credentials;

• appropriate error and response policies;

• specific controls for sensitive endpoints and operations.

In APIs that handle critical information or present a considerable exposure surface, Cybersecurity Specialists can participate in architecture, review, and testing of the implemented controls.

An API needs documentation that another team can use

An API is difficult to integrate when its operation depends on the informal knowledge of the developer who built it.

Consumers need to know what endpoints exist, what information they must send, what responses they can receive, and how to act in the event of different errors.

Documentation also reduces friction between teams.

If Mobile needs to continuously wait for Backend to explain how to use each endpoint, the API is not functioning correctly as an interface between the two. A well-defined contract allows different teams to progress with greater autonomy.

OpenAPI can be used to maintain a structured description of HTTP APIs and facilitate the generation of documentation, validations, or other tools around the contract.

The quality of that documentation becomes even more important when consumers are outside the organization. An API for partners or clients needs to be understood without direct access to the team that implemented each service.

API Gateway helps control an ecosystem that is starting to grow

When an architecture exposes numerous services, allowing each consumer to connect directly with each component can quickly increase complexity.

An API Gateway can provide a single entry point for certain APIs and centralize responsibilities such as routing, authentication, rate limiting, observability, or policy enforcement.

This is especially useful in distributed architectures, although introducing a gateway also adds infrastructure that must be designed and operated.

The API Developer can work together with Cloud Engineers to deploy and scale these components, especially when APIs receive high volumes or must operate in different regions.

The infrastructure must respond to the actual requirements of the product. Incorporating gateways, service meshes, or additional layers without a specific need can end up increasing the operational cost of an architecture that was originally simple.

An API in production needs observability

Knowing that an API is available does not necessarily explain how it is functioning.

It may respond correctly to most requests and experience high latencies only on certain endpoints. There may also be an external dependency that generates intermittent errors or a consumer that suddenly increases the volume of requests.

Observability allows for analyzing that behavior.

Metrics such as latency, throughput, error rates, and utilization can be combined with logs and tracing to investigate what happens when an operation traverses multiple components.

In distributed architectures, this capability is especially important because a request can traverse multiple services before producing a response.

DevOps Engineers can help incorporate observability, alerts, and automation within the operational cycle of APIs.

API testing should check more than the happy path

An API may work perfectly when it receives exactly the expected information and fail when conditions change.

Incomplete requests, invalid data, insufficient permissions, unavailable external services, or usage limits are part of the behavior that needs to be checked.

Testing can cover contracts, integration, security, performance, and compatibility between versions. QA Engineers can automate critical scenarios to detect regressions before a change reaches consumers.

This is especially important when different applications depend on the same API.

A change that works correctly for a new client may introduce an incompatibility with an older version of the mobile application still used by thousands of users.

When does a company need an API developer?

Not all organizations need a specialist dedicated exclusively to API development.

In a relatively simple application, a Backend Developer can perfectly design the necessary endpoints and maintain them alongside the rest of the server logic.

The need for specialization increases when APIs cease to be a secondary component and begin to structure how the technological ecosystem functions.

Some signs are:

• multiple applications consume the same services;

• the number of integrations with external platforms increases;

• partners or clients need to consume the company's APIs;

• Backend changes frequently break consumers;

• there are recurring versioning or documentation issues;

• the architecture uses numerous services or microservices;

• security, availability, and performance of the APIs have a direct impact on the business.

A company that recognizes several of these situations likely needs to treat API design as a core capability and not as an additional task within each project.

Backend developer vs API developer: where is the difference?

A Backend Developer can work on business logic, databases, processing, integrations, authentication, and APIs. Their scope can cover a large part of an application's server.

The API Developer represents a specialization within that domain.

Their focus is on the interfaces that connect systems and on keeping them usable throughout their lifecycle. Contract design, consumer experience, versioning, documentation, governance, security, and observability gain greater weight.

The difference is especially noticeable when a company moves from having an application that uses an API to maintaining an ecosystem that depends on many APIs.

In the first scenario, reinforcing the team with an experienced Backend Developer may be sufficient. In the second, having specific experience in API design and management can significantly reduce the accumulated complexity.

When the API is part of the product, its quality is no longer a technical detail

An internal API may start as a way to communicate between two applications and end up becoming a piece used by multiple teams, clients, and partners.

At that point, modifying it has broader consequences.

The company needs to maintain stable contracts, control who accesses it, observe how it is used, and have a strategy for introducing changes without interrupting existing consumers.

This is where the specialization of an API Developer adds the most value.

The decision to incorporate this profile should depend on the weight that APIs have within the architecture. When they connect a significant part of the product or directly represent a capability offered to third parties, treating them as simple endpoints developed independently is no longer sufficient.

A well-designed API allows different systems to evolve while maintaining predictable interfaces between them. When those interfaces become business infrastructure, the profile responsible for designing and maintaining them also becomes strategic.