Implement a skill for use in Copilot Studio

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APPLIES TO: SDK v4

A skill is a bot that can be used by another bot. In this way, you can create a single user-facing bot and extend it with one or more skills. You can learn more about skills in general in Skills Overview, and how to build them in Implement a skill. Alternatively, the Virtual Assistant templates contain a set of prebuilt skills you can customize and deploy instead of building one from scratch.

If you expect that your skill will be consumed from a Copilot Studio copilot, there are some other restrictions placed on your skill you must account for.

Manifest restrictions

Copilot Studio places restrictions on what you can declare in your skill manifest.

  • You can declare only 100 or fewer actions.
  • Each action is limited to 25 or fewer inputs or outputs.
  • You can't use the array type for inputs or outputs.

Same-tenant restriction

In order to ensure compliance and adequate governance of custom skills being registered for use within Copilot Studio, your skill bot must be a registered application in Microsoft Entra ID. Upon adding a skill, we validate if the skill's application ID is in the tenant of the signed in user and the skills endpoint matches the registered application's Home Page URL.

Before you can register your bot as a skill within Copilot Studio, you must ensure that for the bot, the home page in the Azure portal is set to the bot's skill manifest URL.

Validation performed during registering a Skill

When an end user attempts to connect to your skill from their copilot, they'll first need to import the skill to Copilot Studio. Your skill goes through a series of validation checks. A failure of one of these checks might result in an error message as described in this table.

Validation step Error code Error message Description or mitigation
Manifest URL is valid URL_MALFORMED, URL_NOT_HTTPS The link isn't valid; The link must begin with https:// Reenter the link as a secure URL.
Manifest is retrievable MANIFEST_FETCH_FAILED We ran into problems getting the skill manifest. Verify your manifest URL is a link to your manifest; try opening your manifest URL in a web browser. If the URL renders the page within 10 seconds, re-register your skill.
Manifest is readable MANIFEST_TOO_LARGE The manifest is too large. Your manifest must be 500 KB or less.
Manifest is readable MANIFEST_MALFORMED The manifest is incompatible. Check if the manifest is a valid JSON file. Check if the manifest contains required properties, such as name, msaAppId, and so on. See Manifest restrictions for more information.
Skill isn't yet registered MANIFEST_ALREADY_IMPORTED This skill has already been added to your bot. Delete the skill and register it again.
Manifest endpoint and homepage domains match MANIFEST_ENDPOINT_ORIGIN_MISMATCH There's a mismatch in your skill endpoints. You Microsoft Entra ID app's homepage URL domain and manifest URL domain must match. See Same-tenant restriction
Skill is hosted in signed in user's tenant APPID_NOT_IN_TENANT To add a skill, it must first be registered. A global administrator must register the skill into the signed in user's organization.
Actions are limited LIMITS_TOO_MANY_ACTIONS The skill is limited to 100 actions. There are too many skill actions defined in skill manifest. Remove actions and try again.
Action input parameters are limited LIMITS_TOO_MANY_INPUTS Actions are limited to 25 inputs. There are too many skill action input parameters. Remove parameters and try again.
Action output parameters are limited LIMITS_TOO_MANY_OUTPUTS Actions are limited to 25 outputs. There are too many skill action output parameters. Remove parameter and try again.
Skill count is limited LIMITS_TOO_MANY_SKILLS Your bot can have a maximum of 25 skills. There are too many skills added into a bot. Remove an existing skill and try again.
Security token is valid AADERROR_OTHER It looks like something went wrong. There might be a transient error to acquire a security token to trigger the skill. Retry importing the skill.
Skill is healthy ENDPOINT_HEALTHCHECK_FAILED, HEALTH_PING_FAILED Something went wrong while checking your skill. Copilot Studio received an unknown response when sending an EndOfConversation activity to your skill. Make sure your skill is running and responding correctly.
Skill is authorized ENDPOINT_HEALTHCHECK_UNAUTHORIZED This skill hasn't allow-listed your bot. Check if your bot is to the skill's allow list. For more information, see the Copilot Studio how to Configure a Skill .