Is a plug-in the same as an extension?

In most platforms the words are used for the same thing: code that the host loads at a defined extension point. Some platforms reserve one of the terms for a particular packaging format.

Why can an extension not simply call any internal function of the host?

Only documented APIs are part of the contract. Internal functions can change without notice, and the sandbox usually blocks them.

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Context card

Extension points of a platform

How does a platform SDK let outside code extend a host application?

By knowledge.aitechdoc.world

Reviewed September 29, 2026

Review log and changes

The short answer

A platform SDK defines where and how outside code may plug into a host application: named extension points, a manifest that declares what the extension contributes and which permissions it needs, APIs the extension may call and usually a sandbox that isolates it. The host loads the extension and calls it at the declared points — control stays with the host.

For: Developers and technical writers building or documenting extensions

Key points

Extension points are the places where the host accepts contributions — commands, views, data hooks.
A manifest declares what the extension adds and which permissions it requests.
The host calls the extension (inversion of control), not the other way round.
Sandboxing and permission scopes limit what an extension can reach.
Compatibility promises and deprecation paths decide how long an extension keeps working.

The context

Host and extension

A platform SDK is a software framework in the strict sense: the host application defines the structure and calls the extension. The SDK documents the extension points, supplies the APIs the extension may call and tools to build, test and publish it.

Manifest and permissions

A manifest lists the extension's contributions and the scopes it needs. Authorization is enforced by the host: an extension that has not requested access to data does not get it. Many platforms run extensions in a sandbox or on the platform's own runtime.

Why the contract matters

Extensions depend on the host's interface contract. Backward compatibility and published deprecation paths decide whether an extension survives the next host release.

See the encyclopedia article Platform SDKs.

Questions readers ask next

Is a plug-in the same as an extension?: In most platforms the words are used for the same thing: code that the host loads at a defined extension point. Some platforms reserve one of the terms for a particular packaging format.
Why can an extension not simply call any internal function of the host?: Only documented APIs are part of the contract. Internal functions can change without notice, and the sandbox usually blocks them.

Sources

Extension API — Visual Studio Code
Forge — Atlassian Developer

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 framework
In software engineering, a software framework is a reusable software structure that provides generic functionality and a defined control flow, into which developers insert application-specific code at designated extension points.
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.
Authorization
In industrial cybersecurity, authorization is the determination of which actions an authenticated user, device or system is permitted to perform. It is usually implemented through roles and permissions following the principle of least privilege.
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.
Backward compatibility
In systems engineering, backward compatibility is the controlled ability of a new version to work with older data, interfaces or peer systems. It is a defined and tested property, not an assumption that old inputs will still be handled.
Deprecation path
In systems engineering, a deprecation path is a controlled plan for announcing, replacing, migrating and removing an old version or function. It gives dependents a defined period and a defined route to move away from what is being retired.
Low-code/no-code platform
In software engineering, a low-code/no-code platform is a development environment that lets users build applications largely through graphical configuration, templates and drag-and-drop components, with little or no hand-written code.