--- title: "Slash commands" sidebar_position: 30 --- Slash commands are messages that begin with `/` and trigger an HTTP request to a web service that can in turn post one or more messages in response. Slash commands have an additional feature, **autocomplete**, that displays a list of possible commands based on what has been typed in the message box. Typing `/` in an empty message box will display a list of all slash commands. As the slash command is typed in the message box, autocomplete will also display possible arguments and flags for the command. Unlike [outgoing webhooks](/developers/integrate/webhooks/outgoing), slash commands work in private channels and direct messages in addition to public channels, and can be configured to auto-complete when typing. Mattermost includes a number of [built-in slash commands](https://docs.mattermost.com/channels/interact-with-channels.html). You can also create [custom slash commands](/custom). ## Tips and best practices 1. Slash commands are designed to easily allow you to post messages. For other actions such as channel creation, you must also use the [Mattermost APIs](https://api.mattermost.com). 2. Posts size is limited to 16383 characters for servers running [Mattermost Server v5.0 or later](https://docs.mattermost.com/administration/important-upgrade-notes.html). Use the `extra_responses` field to reply to a triggered slash command with more than one post. 3. You can restrict who can create slash commands in [System Console > Integrations > Integration Management](https://docs.mattermost.com/configure/configuration-settings.html#enable-custom-slash-commands). 4. Mattermost [outgoing webhooks](/developers/integrate/webhooks/outgoing) are Slack-compatible. You can copy-and-paste code used for a Slack outgoing webhook to create Mattermost integrations. Mattermost [automatically translates Slack's proprietary JSON payload format](/slack#translate-slacks-data-format-to-mattermost). 5. The external application may be written in any programming language. It needs to provide a URL which receives the request sent by your Mattermost Server and responds with in the required JSON format. ## FAQ ### How do I debug slash commands? To debug slash commands in **System Console > Logs**, set **System Console > Logging > Enable Webhook Debugging** to **true** and set **System Console > Logging > Console Log Level** to **DEBUG**. ### How do I send multiple responses from a slash command? You can send multiple responses with an `extra_responses` parameter as follows. ```http HTTP/1.1 200 OK Content-Type: application/json Content-Length: 696 { "response_type": "in_channel", "text": "\n#### Test results for July 27th, 2017\n@channel here are the requested test results.\n\n| Component | Tests Run | Tests Failed |\n| ---------- | ----------- | ---------------------------------------------- |\n| Server | 948 | :white_check_mark: 0 |\n| Web Client | 123 | :warning: 2 [(see details)](http://linktologs) |\n| iOS Client | 78 | :warning: 3 [(see details)](http://linktologs) |\n\t\t ", "username": "test-automation", "icon_url": "https://www.mattermost.org/wp-content/uploads/2016/04/icon.png", "props": { "test_data": { "ios": 78, "server": 948, "web": 123 } }, "extra_responses": [ { "text": "message 2", "username": "test-automation" }, { "text": "message 3", "username": "test-automation" } ] } ``` ### What if my slash command takes time to build a response? Reply immediately with an `ephemeral` message to confirm response of the command, and then use the `response_url` to send up to five additional messages within a 30-minute time period from the original command invocation. ### Why does my slash command fail to connect to `localhost`? By default, Mattermost prohibits outgoing connections that resolve to certain common IP ranges, including the loopback (`127.0.0.0/8`) and various private-use subnets. During development, you may override this behaviour by setting `ServiceSettings.AllowedUntrustedInternalConnections` to `"127.0.0.0/8"` in your `config.json` or via **System Console > Advanced > Developer**. See the [configuration settings documentation](https://docs.mattermost.com/configure/environment-configuration-settings.html#allow-untrusted-internal-connections) for more details. ### Should I configure my slash command to use `POST` or `GET`? Best practice suggests using `GET` only if a request is considered idempotent. This means that the request can be repeated safely and can be expected to return the same response for a given input. Some servers hosting your slash command may also impose a limit to the amount of data passed through the query string of a `GET` request. Ultimately, however, the choice is yours. If in doubt, configure your slash command to use a `POST` request. Note that slash commands configured to use a GET request were broken prior to Mattermost release 5.0.0. The payload was incorrectly encoded in the body of the GET request instead of in the query string. While it was still technically possible to extract the payload, this was non-standard and broke some development stacks. ### Why does my slash command always fail with `returned an empty response`? If you are emitting the `Content-Type: application/json` header, your body must be valid JSON. Any JSON decoding failure will result in this error message. Also, you must provide a `response_type`. Mattermost does not assume a default if this field is missing. ### Why does my slash command print the JSON data instead of formatting it? Ensure you are emitting the `Content-Type: application/json` header, otherwise your body will be treated as plain text and posted as such. ### Are slash commands Slack-compatible? See the [Slack compatibility](/slack) page. ### How do I use Bot Accounts to reply to slash commands? #### If you are developing an integration - Set up a [Personal Access Token](/developers/integrate/reference/personal-access-token) for the Bot Account you want to reply with. - Use the [REST API](https://api.mattermost.com/#tag/posts/operation/CreatePost) to create a post with the Access Token. #### If you are developing a plugin Use [`CreatePost`](/developers/integrate/reference/server#API.CreatePost) plugin API. Make sure to set the `UserId` of the post to the `UserId` of the Bot Account. If you want to create an ephemeral post, use [`SendEphemeralPost`](/developers/integrate/reference/server#API.SendEphemeralPost) plugin API instead. ## Troubleshoot slash commands Join the [Mattermost user community](https://mattermost.com/pl/default-ask-mattermost-community) for help troubleshooting your slash command. ## Share your integration If you've built an integration for Mattermost, please consider [sharing your work](/developers/integrate/getting-started) in our [Marketplace](https://mattermost.com/marketplace/). The [Marketplace](https://mattermost.com/marketplace/) lists open source integrations developed by the Mattermost community and are available for download, customization, and deployment to your private cloud or self-hosted infrastructure.