Starts a Real Time Messaging session.


Method access

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Content types

  • Rate limits

    Tier 1
  • Arguments


    Authentication token bearing required scopes. Tokens should be passed as an HTTP Authorization header or alternatively, as a POST parameter.


    Batch presence deliveries via subscription. Enabling changes the shape of presence_change events. See batch presence.

    Default: false


    Set this to true to receive the locale for users and channels. Defaults to false


    Returns MPIMs to the client in the API response.


    Exclude latest timestamps for channels, groups, mpims, and ims. Automatically sets no_unreads to 1

    Default: 0


    Skip unread counts for each channel (improves performance).


    Only deliver presence events when requested by subscription. See presence subscriptions.

    Default: true


    Return timestamp only for latest message object of each channel (improves performance).


    Present arguments as parameters in application/x-www-form-urlencoded querystring or POST body. This method does not currently accept application/json.

    Example responses

    Common successful response

    Typical success response

        "ok": true
    Common error response

    Typical error response

        "ok": false,
        "error": "invalid_auth"

    This method begins a Real Time Messaging API session and reserves your application a specific URL with which to connect via websocket.

    It's user-centric and team-centric: your app connects as a specific user or bot user on a specific team. Many apps will find the Events API's subscription model more scalable when working against multiple teams.

    This method also returns a smorgasbord of data about the team, its channels, and members. Some times more information than can be provided in a timely or helpful manner.

    Please use rtm.connect instead, especially when connecting on behalf of an Enterprise Grid customer.

    Consult the RTM API documentation for full details on using the RTM API. You'll also find our changelog entry useful.

    The members array found in this and other methods will begin automatically truncating at 1,500 and eventually fewer results beginning December 1, 2017. As of March, 2018 the cap is 500. Please Use conversations.members to manage memberships instead. Read on to learn more.

    New Slack apps may not use any Real Time Messaging API method. Create a classic app and use the V1 Oauth flow to use RTM.

    For most applications, Socket Mode is a better way to communicate with Slack.

    Note that setting no_latest=1 will automatically set no_unreads=1.

    This method returns lots of data about the current state of a team, along with a WebSocket Message Server URL:

        "ok": true,
        "url": "wss:\/\/\/websocket\/7I5yBpcvk",
        "self": {
            "id": "U023BECGF",
            "name": "bobby",
            "prefs": {
            "created": 1402463766,
            "manual_presence": "active"
        "team": {
            "id": "T024BE7LD",
            "name": "Example Team",
            "email_domain": "",
            "domain": "example",
            "icon": {
            "msg_edit_window_mins": -1,
            "over_storage_limit": false
            "prefs": {
            "plan": "std"
        "users": [ ... ],
        "channels": [ ... ],
        "groups": [ ... ],
        "mpims": [ ... ],
        "ims": [ ... ],
        "bots": [ ... ],

    The url property contains a WebSocket Message Server URL. Connecting to this URL will initiate a Real Time Messaging session. These URLs are only valid for 30 seconds, so connect quickly!

    The self property contains details on the authenticated user.

    The team property contains details on the authenticated user's team. If a team has not yet set a custom icon, the value of team.icon.image_default will be true.

    The users property contains a list of user objects, one for every member of the team. presence is no longer included for users. The list of users may truncate on especially long teams. Use Web API methods to retrieve information about users instead.

    The channels property is a list of channel objects, one for every channel visible to the authenticated user. For regular or administrator accounts this list will include every team channel. The is_member property indicates if the user is a member of this channel. If true then the channel object will also include the topic, purpose, member list and read-state related information. The latest, unread_count, and unread_count_display attributes have been removed from this method's response. See this changelog entry.

    The groups property is a list of group objects, one for every group the authenticated user is in.

    The mpims property is a list of mpims objects, one for every group the authenticated user is in. MPIMs are only returned to the client if mpim_aware is set when calling rtm.start. Otherwise, mpims are emulated using the groups API.

    The ims property is a list of IM objects, one for every direct message channel visible to the authenticated user.

    The bots property gives details of the integrations set up on this team.


    This table lists the expected errors that this method could return. However, other errors can be returned in the case where the service is down or other unexpected factors affect processing. Callers should always check the value of the ok params in the response.


    Workspace is being migrated between servers. See the team_migration_started event documentation for details.


    For large teams please use rtm.connect instead of rtm.start.

    user_removed_from_team [hidden]user removed from team (generated)
    grpc_userLogin_fail [hidden]grpc userLogin fail (generated)
    too_many_channels [hidden]too many channels (generated)

    No authentication token provided.


    Some aspect of authentication cannot be validated. Either the provided token is invalid or the request originates from an IP address disallowed from making the request.


    Authentication token is for a deleted user or workspace when using a bot token.


    Authentication token is for a deleted user or workspace or the app has been removed when using a user token.


    Authentication token has expired


    The workspace token used in this request does not have the permissions necessary to complete the request. Make sure your app is a member of the conversation it's attempting to post a message to.


    The workspace is undergoing an enterprise migration and will not be available until migration is complete.


    Administrators have suspended the ability to post a message.


    The token used is not granted the specific scope permissions required to complete this request.


    The token type used in this request is not allowed.


    The method has been deprecated.


    The endpoint has been deprecated.


    Two factor setup is required.


    The method cannot be called from an Enterprise.


    The method was either called with invalid arguments or some detail about the arguments passed are invalid, which is more likely when using complex arguments like blocks or attachments.


    The method was passed an argument whose name falls outside the bounds of accepted or expected values. This includes very long names and names with non-alphanumeric characters other than _. If you get this error, it is typically an indication that you have made a very malformed API call.


    The method was passed an array as an argument. Please only input valid strings.


    The method was called via a POST request, but the charset specified in the Content-Type header was invalid. Valid charset names are: utf-8 iso-8859-1.


    The method was called via a POST request with Content-Type application/x-www-form-urlencoded or multipart/form-data, but the form data was either missing or syntactically invalid.


    The method was called via a POST request, but the specified Content-Type was invalid. Valid types are: application/json application/x-www-form-urlencoded multipart/form-data text/plain.


    The method was called via a POST request and included a data payload, but the request did not include a Content-Type header.


    The workspace associated with your request is currently undergoing migration to an Enterprise Organization. Web API and other platform operations will be intermittently unavailable until the transition is complete.

    invalid_json [hidden]The method was called via a `POST` request with `Content-Type` `application/json`, but the body was not valid JSON.
    json_not_object [hidden]The method was called via a `POST` request a valid JSON body, but the JSON value was not an object.

    The request has been ratelimited. Refer to the Retry-After header for when to retry the request.


    Access to this method is limited on the current network


    The method was called via a POST request, but the POST data was either missing or truncated.

    upgrade_required [hidden]The calling application needs to be upgraded.

    The service is temporarily unavailable


    The server could not complete your operation(s) without encountering a catastrophic error. It's possible some aspect of the operation succeeded before the error was raised.


    The server could not complete your operation(s) without encountering an error, likely due to a transient issue on our end. It's possible some aspect of the operation succeeded before the error was raised.


    This table lists the expected warnings that this method will return. However, other warnings can be returned in the case where the service is experiencing unexpected trouble.


    A members array included in a channel object was truncated at 1500 results. Use conversations.members to retrieve all results.


    The method was called via a POST request, and recommended practice for the specified Content-Type is to include a charset parameter. However, no charset was present. Specifically, non-form-data content types (e.g. text/plain) are the ones for which charset is recommended.


    The method was called via a POST request, and the specified Content-Type is not defined to understand the charset parameter. However, charset was in fact present. Specifically, form-data content types (e.g. multipart/form-data) are the ones for which charset is superfluous.


    Need a token? Create and install a Slack app to begin.
    This will make a real API request. Beware of using it with live workspaces.

    API response

    Submit your arguments to see the API response

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