This is reference for anyone who needs it in order to create a message extension (previously called compose extension) in MS Teams. If you stray outside of the TS/C# world, it’s a pain to find all of this out.

This reference was working as of 24 AUG 2023. It details making a message extension that can search and has a settings page.

Prereqs: you’ll need a Bot, created in dev.teams.microsoft.com > Tools > Bot Management.

manifest.json

{
    "$schema": "https://developer.microsoft.com/en-us/json-schemas/teams/v1.16/MicrosoftTeams.schema.json",
    "manifestVersion": "1.16",
    "composeExtensions":
    [
        {
            "botId": "abcd1235-abcd-1234-abcd-abcd1234abcd",
            "canUpdateConfiguration": true,
            "commands":
            [
                {
                    "id": "search",
                    "type": "query",
                    "title": "Search",
                    "description": "Search...",
                    "initialRun": true,
                    "fetchTask": false,
                    "context":
                    [
                        "commandBox",
                        "compose"
                    ],
                    "parameters":
                    [
                        {
                            "name": "q",
                            "title": "Search term",
                            "description": "e.g. jobs, cars, holidays...",
                            "inputType": "text"
                        }
                    ]
                }
            ],
            "messageHandlers":
            [
                {
                    "type": "link",
                    "value":
                    {
                        "domains":
                        [
                            "example.com"
                        ]
                    }
                }
            ]
        }
    ],
    "validDomains":
    [
        "example.com"
    ],
}

In your app controller that handles POST requests from the Bot, you’ll receive the following types of payloads:

# Request
{
    "type": "invoke",
    "name": "composeExtension/querySettingUrl"
}

# Response
{
    "composeExtension": {
        "type": "config"
        "suggestedActions": {
            "actions": [
                {
                    "type": "openApp",
                    "title": "Settings",
                    "value": "https://example.com/settings"
                },
            ],
        },
    }
}