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+---
+slug: "9f9f"
+authors: silverpill <@silverpill@mitra.social>
+type: informational
+status: DRAFT
+discussionsTo: https://codeberg.org/silverpill/feps/issues
+dateReceived: 2026-04-03
+---
+# FEP-9f9f: Collections
+
+## Summary
+
+This document describes the current best practices for implementing and using [ActivityPub] collections.
+
+Some parts of it are based on the implementation of collections in [GoActivityPub](https://github.com/go-ap).
+
+## Requirements
+
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC-2119].
+
+## What is a collection?
+
+### Activity Streams definition
+
+[Activity Streams 2.0](https://www.w3.org/TR/activitystreams-core/#dfn-collectionpage): A collection is an object with `Collection` type or its subtype (e.g. `OrderedCollection`).
+
+### Duck typing
+
+[FEP-2277]: A collection is an object with `items`, `orderedItems`, `totalItems`, `partOf`, `first`, `last`, `next`, `prev` or `current` property.
+
+## Ownership
+
+A collection SHOULD have an `attributedTo` property indicating the actor that created it.
+
+## Creating collections
+
+Clients can create collections by publishing a `Create` activity where `object` is a collection. The server MUST ignore reserved collection properties such as `items`, `totalItems` and pagination properties.
+
+Some special collections, such as `inbox` and `outbox` are created automatically by a server.
+
+Servers MAY create collections automatically when the `object` of `Create` activity contains a property that points to a collection, such as `likes`, `shares` or `replies`. When the specified collection ID is local, the server MUST verify that the ID is valid, and MAY assign a different ID.
+
+Clients MUST NOT embed non-anonymous collections in objects.
+
+Collection IDs SHOULD NOT contain query parameters.
+
+## Updating collections
+
+The contents of a collection are modified either directly by `Add`, `Remove` and `Move` activities, or indirectly by side-effects of other activities.
+
+A client can update other properties of a collection by generating an `Update` activity. The server MUST NOT overwrite reserved collection properties such as `items`, `totalItems` and pagination properties.
+
+> [!NOTE]
+> `Update` of a collection is not compatible with client-side signing (FEP-ae97) because partial updates are not supported there.
+
+## Ordering
+
+ActivityPub requires `OrderedCollection` to be presented in [reverse chronological order][AP-Collections], though in practice some ordered collections are presented in forward chronological order.
+
+## Filtering
+
+Collections can be filtered.
+
+Filters are specified using query parameters that are appended to a collection ID. A set of guidelines for using these parameters has been proposed in [FEP-6606: ActivityPub client to server collections addressing conventions][FEP-6606].
+
+## Pagination
+
+Pagination of collections is described in [Activity Streams 2.0][AS-Paging].
+
+Collection page IDs are usually created by appending query parameters to a collection ID:
+
+- `page` (integer): the page number.
+- `after` and `before` (percent-encoded URI): the item identifier for cursor based pagination.
+- `maxItems` (integer): the maximum number of items in a page.
+
+## Access control
+
+Collections SHOULD be filtered based on the permissions of a user.
+
+However, a collection itself usually doesn't have an audience and is treated as public by default.
+
+## Addressing
+
+An object can be addressed to a collection. When determining delivery targets and regulating access to an object, the server SHOULD expand collections by replacing them with actors they contain (if any).
+
+### `Public` collection
+
+`https://www.w3.org/ns/activitystreams#Public` is a special collection ID that is used for public addressing. It is described in [ActivityPub][AP-Public].
+
+## References
+
+- Christine Lemmer-Webber, Jessica Tallon, Erin Shepherd, Amy Guy, Evan Prodromou, [ActivityPub], 2018
+- James M Snell, Evan Prodromou, [Activity Streams 2.0][ActivityStreams], 2017
+- S. Bradner, [Key words for use in RFCs to Indicate Requirement Levels][RFC-2119], 1997
+- silverpill, [FEP-2277: ActivityPub core types][FEP-2277], 2025
+- Marius Orcsik, [FEP-6606: ActivityPub client to server collections addressing conventions][FEP-6606], 2024
+
+[ActivityPub]: https://www.w3.org/TR/activitypub/
+[ActivityStreams]: https://www.w3.org/TR/activitystreams-core/
+[RFC-2119]: https://tools.ietf.org/html/rfc2119.html
+[FEP-2277]: https://codeberg.org/fediverse/fep/src/branch/main/fep/2277/fep-2277.md
+[FEP-6606]: https://codeberg.org/fediverse/fep/src/branch/main/fep/6606/fep-6606.md
+[AS-Paging]: https://www.w3.org/TR/activitystreams-core/#paging
+[AP-Collections]: https://www.w3.org/TR/activitypub/#collections
+[AP-Public]: https://www.w3.org/TR/activitypub/#public-addressing
+
+## Copyright
+
+CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
+
+To the extent possible under law, the authors of this Fediverse Enhancement Proposal have waived all copyright and related or neighboring rights to this work.