Can I use an API without its SDK?

Usually yes, by sending the requests directly. The SDK saves work and reduces mistakes, for example in token handling or retries.

Is a client library the same as an SDK?

A client library is the core of a developer SDK. The SDK usually adds tools, samples and documentation around it.

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Context card

SDK vs. API

What is the difference between an SDK and an API?

By knowledge.aitechdoc.world

Reviewed September 29, 2026

Review log and changes

The short answer

An API is an interface: the contract of operations, data formats and rules through which one piece of software uses another. An SDK is a kit built around one or more APIs — libraries in a given programming language, authentication helpers, samples, tools and documentation — that makes the API easier and safer to use. An API can exist without an SDK; an SDK always rests on some interface.

For: Technical writers and developers documenting APIs and SDKs

Key points

The API defines what can be called, with which data and which responses.
The SDK implements calls to it in a programming language and handles authentication, retries, pagination and errors.
Several SDKs in different languages can wrap the same API; many are generated from a machine-readable interface description.
Versioning concerns both: an API version changes the contract, an SDK version changes the library.

The context

Contract and kit

An application programming interface is a contract. For a REST API it lists endpoints, methods, parameters, data formats and error codes. The interface contract holds whether or not any client library exists.

A software development kit is built on top: software libraries that turn API calls into functions of a programming language, helpers for authentication, handling of limits and errors, samples and reference documentation.

Why the difference matters

Documentation for an API describes the contract; documentation for an SDK describes how to use the library — installation, configuration, idiomatic calls. Both need versions: semantic versioning of the SDK does not replace versioning of the API it calls.

See the encyclopedia article Developer SDKs.

Questions readers ask next

Can I use an API without its SDK?: Usually yes, by sending the requests directly. The SDK saves work and reduces mistakes, for example in token handling or retries.
Is a client library the same as an SDK?: A client library is the core of a developer SDK. The SDK usually adds tools, samples and documentation around it.

Sources

OpenAPI Specification — OpenAPI Initiative
RFC 6749: The OAuth 2.0 Authorization Framework — IETF, October 1, 2012

Review log and changes

Every context card is checked against its sources before it is published, and again whenever it changes; the date under the byline is the last review. Corrections (something was wrong) and additions (something was missing) are logged below with date and time (Berlin time). Typos, formatting and link fixes are not listed.

Reviewed September 29, 2026

No corrections or additions since publication.

Glossary terms on this card

Software development kit (SDK)
In software engineering, a software development kit (SDK) is a collection of libraries, tools, documentation and samples that developers use to build applications for a specific platform, device, protocol or service.
Application programming interface (API)
In software engineering, an application programming interface (API) is a defined set of functions, data structures, messages or endpoints through which one software component offers services to other components, together with the rules for using them. In industrial automation, APIs connect control software, engineering tools, MES, cloud services and custom applications.
REST API
In software engineering, a REST API is an application programming interface that follows the REST (Representational State Transfer) architectural style: resources are identified by URLs and manipulated with standard HTTP methods such as GET, POST, PUT and DELETE, typically exchanging JSON, with stateless requests.
Software library
In software engineering, a software library is a collection of reusable, precompiled or source-level functions, classes or function blocks that programs call to perform common tasks.
Authentication
In industrial cybersecurity, authentication is the verification of the identity of a user, device or system before it is granted access. It answers the question “who is this?”, not “what may they do?”.
Interface contract
In software engineering, an interface contract is the explicit specification of the mutual obligations between a component and its users at an interface, including preconditions the caller must meet, postconditions and guarantees the component provides, invariants, error behavior and timing.
Semantic versioning
In software engineering, semantic versioning is a versioning convention with identifiers in the form MAJOR.MINOR.PATCH, where the major number changes for incompatible changes, the minor number for backward-compatible features and the patch number for backward-compatible fixes.