title: About building Copilot Extensions

intro: 'Learn about the development process for {% data variables.product.prodname_copilot_extensions_short %}.'

versions:

feature: copilot-extensions

topics:

* Integrate their tool into the developer workflow on {% data variables.product.company_short %} and the IDE

* Leverage the {% data variables.product.company_short %} ecosystem to raise awareness for their product

{% data reusables.copilot.copilot-extensions.differences-between-agents-and-skillsets-1 %}

For more information about context passing, see [AUTOTITLE](/copilot/building-copilot-extensions/building-a-copilot-agent-for-your-copilot-extension/context-passing-for-your-agent).

{% data variables.product.company_short %} provides a comprehensive toolkit for extension builders, with code samples, a CLI debugging tool, quickstart SDKs, and a user feedback repository. For more information, see the [copilot-extensions](https://github.com/orgs/copilot-extensions/) organization on {% data variables.product.company_short %}.

type: overview

{% data variables.product.prodname_copilot_agents_short %} are custom tools embedded in {% data variables.product.prodname_copilot_extensions_short %}. They integrate with {% data variables.product.prodname_copilot_chat_short %} to provide additional functionalities tailored to specific needs. {% data variables.product.prodname_copilot_agents_short %} can perform various tasks such as querying documentation, retrieving data, executing specific actions, or providing AI-assisted coding suggestions. They enhance the capabilities of {% data variables.product.prodname_copilot %} by allowing developers to build and integrate custom features directly into the {% data variables.product.prodname_copilot_chat_short %} interface.

To use a {% data variables.product.prodname_copilot_agent_short %} in {% data variables.product.prodname_copilot_chat_short %}, it must be associated with a {% data variables.product.prodname_github_app %}. This combination of a {% data variables.product.prodname_github_app %} and a {% data variables.product.prodname_copilot_agent_short %} is what we refer to as a {% data variables.product.prodname_copilot_extension %}. For more information on {% data variables.product.prodname_copilot_extensions_short %}, see [AUTOTITLE](/copilot/building-copilot-extensions/about-building-copilot-extensions).

type: reference

{% data reusables.copilot.copilot-extensions.agents-copilot-platform-prerequisites %}

layout: inline

{% data variables.product.prodname_copilot_agents_short %} communicate with the {% data variables.product.prodname_copilot_short %} platform in the form of server-sent events (SSEs). Rather than waiting for the {% data variables.product.prodname_copilot_short %} platform to request an update from your agent, or vice versa, you can use SSEs to send and receive updates to and from the platform in real time.

To learn more about SSEs, see [Server-sent events](https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events) in the mdn documentation.

allowTitleToDifferFromFilename: true

{% data variables.product.prodname_copilot_short %}'s Language Learning Model (LLM) is a powerful, large-scale language model that is trained on a diverse range of data sources, including code, documentation, and other text. {% data variables.product.prodname_copilot_short %}'s LLM underpins the functionality for {% data variables.product.prodname_copilot %}, and is used to power all of {% data variables.product.prodname_copilot_short %}'s features, including code generation, documentation generation, and code completion.

To authenticate, use the same `X-Github-Token` header sent to your agent. For more information, see [AUTOTITLE](/copilot/building-copilot-extensions/building-a-copilot-agent-for-your-copilot-extension/configuring-your-copilot-agent-to-communicate-with-github#fetching-resources-from-the-github-api).

type: overview

A skill within {% data variables.product.prodname_copilot %} is a tool that the model calls to perform a specific task in response to a user query. A skillset is a collection of these skills (up to five per skillset). {% data variables.product.prodname_copilot_skillsets %} provide a streamlined way to extend {% data variables.product.prodname_copilot_short %}’s functionality, allowing builders to integrate external services or custom API endpoints into their {% data variables.product.prodname_copilot_short %} workflow. With skillsets, builders can enable {% data variables.product.prodname_copilot_short %} to perform tasks—such as retrieving data or executing actions in third-party services—without needing to manage complex workflows or architecture.

For a quickstart example of a skillset, see the [skillset-example](https://github.com/copilot-extensions/skillset-example) repository. For information on building a skillset, see [AUTOTITLE](/copilot/building-copilot-extensions/building-a-copilot-skillset-for-your-copilot-extension/building-copilot-skillsets).

type: how_to

{% data variables.product.prodname_copilot_skillsets %} are a streamlined way to extend {% data variables.product.prodname_copilot %}'s functionality by defining API endpoints that {% data variables.product.prodname_copilot_short %} can call. When you create a skillset, {% data variables.product.prodname_copilot_short %} handles all the AI interactions while your endpoints provide the data or functionality. This guide walks you through configuring and deploying a skillset within your {% data variables.product.prodname_github_app %}.