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Paginating through collections

Throughout the Slack platform, you'll encounter collections of things. Lists of users. Arrays of channels. A pride of lion emoji.

When you call an API method to retrieve most of these collections, they're returned to you in portions. Check out more detail below on pagination in API methods, including how to use them and which methods follow the pattern.

Most methods that support pagination use a cursor-based approach. However, some older methods use varied versions of pagination. The individual documentation for each API method is your source of truth for which pattern the method follows.

Overview: cursor-based pagination

For larger collections like channel and user lists, Slack API methods return results using a cursor-based approach.

Cursors are like pointers. Pointers point at things: they reference a specific iota, a place in the list where your last request left off. They help avoid loading an entire set just to give you a slice.

A cursor-paginated method returns two things: a portion of the total set of results, and a cursor that points to the next portion of the results.

Cursor-based pagination is spreading across the platform quickly and is mandatory on some methods.

Please paginate along with us.

Just the factoids

  • Cursor-paginated methods accept cursor and limit parameters.
  • If you don't pass a cursor parameter, but do pass a limit parameter, the default value retrieves the first portion (or "page") of results. On some methods, when apps created before Monday, August 7th pass neither cursor nor limit to the method, the behavior defaults to classic pagination (yuck!).
  • Paginated responses include a top-level response_metadata object that includes a next_cursor when there are additional results to be retrieved.
  • On your next call to the same method, set the cursor parameter equal to the next_cursor value you received on the last request to retrieve the next portion of the collection.
  • An empty, null, or non-existent¬†next_cursor in the response indicates no further results.
  • The limit parameter sets a maximum number of results to return per call.
  • Provide sensible limit values. We recommend 100-200 results at a time.
  • The limit parameter maximum is 1000 and subject to change and may vary per method.
  • It's possible to receive fewer results than your specified limit, even when there are additional results to retrieve. Avoid the temptation to check the size of results against the limit to conclude the results have been completely returned. Instead, check the next_cursor value in the response_metadata object to make sure that it's empty, null, or non-existent.

Walkthrough

When accessing the first virtual page of a paginated collection — for instance making a users.list request for the first time — you'll receive a response_metadata attribute containing a cursor for your next request.

Here's an example request to users.list, where we limit our list of users to 2 users per "page", making it easier to test on a workspace with a low number of users.

GET slack.com/api/users.list?limit=2&token=xoxp-1234-5678-90123

In return, we get our typical users.list response, limited to 2 results. Skip down to the bottom to see the response_metadata, containing cursor information on the next page of results.

{
    "ok": true,
    "members": [
        {
            "id": "USLACKBOT",
            "team_id": "T0G9PQBBK",
            "name": "slackbot",
            "deleted": false,
            "color": "757575",
            "real_name": "slackbot",
            "tz": null,
            "tz_label": "Pacific Daylight Time",
            "tz_offset": -25200,
            "profile": {
                "first_name": "slackbot",
                "last_name": "",
                "image_24": "https:\/\/a.slack-edge.com...png",
                "image_32": "https:\/\/a.slack-edge.com...png",
                "image_48": "https:\/\/a.slack-edge.com...png",
                "image_72": "https:\/\/a.slack-edge.com...png",
                "image_192": "https:\/\/a.slack-edge.com...png",
                "image_512": "https:\/\/a.slack-edge.com...png",
                "avatar_hash": "sv1444671949",
                "always_active": true,
                "real_name": "slackbot",
                "real_name_normalized": "slackbot",
                "fields": null
            },
            "is_admin": false,
            "is_owner": false,
            "is_primary_owner": false,
            "is_restricted": false,
            "is_ultra_restricted": false,
            "is_bot": false,
            "updated": 0
        },
        {
            "id": "W07QCRPA4",
            "team_id": "T0G9PQBBK",
            "name": "glinda",
            "deleted": false,
            "color": "9f69e7",
            "real_name": "Glinda Southgood",
            "tz": "America\/Los_Angeles",
            "tz_label": "Pacific Daylight Time",
            "tz_offset": -25200,
            "profile": {
                "avatar_hash": "8fbdd10b41c6",
                "image_24": "https:\/\/a.slack-edge.com...png",
                "image_32": "https:\/\/a.slack-edge.com...png",
                "image_48": "https:\/\/a.slack-edge.com...png",
                "image_72": "https:\/\/a.slack-edge.com...png",
                "image_192": "https:\/\/a.slack-edge.com...png",
                "image_512": "https:\/\/a.slack-edge.com...png",
                "image_1024": "https:\/\/a.slack-edge.com...png",
                "image_original": "https:\/\/a.slack-edge.com...png",
                "first_name": "Glinda",
                "last_name": "Southgood",
                "title": "Glinda the Good",
                "phone": "",
                "skype": "",
                "real_name": "Glinda Southgood",
                "real_name_normalized": "Glinda Southgood",
                "email": "glenda@south.oz.coven"
            },
            "is_admin": true,
            "is_owner": true,
            "is_primary_owner": true,
            "is_restricted": false,
            "is_ultra_restricted": false,
            "is_bot": false,
            "updated": 1480527098,
            "has_2fa": false
        }
    ],
    "cache_ts": 1498777272,
    "response_metadata": {
        "next_cursor": "dXNlcjpVMEc5V0ZYTlo="
    }
}

Within response_metadata you'll note next_cursor, a string pointing at the next page of results. To retrieve the next page of results, provide this value as the cursor parameter to the paginated method.

Cursor strings typically end with the = character. When presenting this value as a URL or POST parameter, it must be encoded as %3D.

We issue our request for the next page of no more than 2 results like this:

GET slack.com/api/users.list?limit=2&cursor=dXNlcjpVMEc5V0ZYTlo%3D&token=xoxp-1234-5678-90123

And (spoiler alert): we only get one result back. This workspace actually only has three users. We've reached the end of our pagination journey and there are no more results to retrieve. Our next_cursor becomes but an empty string:

{
    "ok": true
    "members": [
        // that one last member
    ],
    "cache_ts": 1498777272,
    "response_metadata": {
        "next_cursor": ""
    }
}

You'll know that there are no further results to retrieve when a next_cursor field contains an empty string (""). You're not even paginating at all if you receive no response_metadata or its next_cursor value.

Cursors expire and are meant to be used within a reasonable amount of time. You should have no trouble pausing between rate limiting windows, but do not persist cursors for hours or days.

Enhanced rate limiting conditions are provided when using cursor-based pagination.

Error conditions

Currently, the only error specific to pagination that you might encounter is:

  • invalid_cursor - Returned when navigating a paginated collection and providing a cursor value that just does not compute — either it's gibberish, somehow encoded wrong, or of too great a vintage.

Invalid limit values are currently magically adjusted to something sensible. We recommend providing reasonable values for best results, as with most parameters.

Methods supporting cursor-based pagination

We're adding cursor-based pagination to almost every collection-yielding method.

Today, cursor-based pagination is supported by these methods:

Please note that when you are trying to page through channels.list, the exclude_members argument won't work too well with pagination at this time. Channels with very large memberships and teams with many channels may cause the method to throw HTTP 500 errors. Please exclude memberships with exclude_members and look them up atomically with channels.info instead.

Classic pagination

You'll find a variety of other pseudo and real pagination schemes through a few other Web API methods.

Each of those API methods detail their pagination strategy.

Timeline methods

These methods are more positional than page oriented and allow you to navigate through time with oldest, latest, and a special inclusive parameter.

Traditional paging

These methods use some form of archaic numeric-based page and count or other limiting parameters.