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matrix-spec/content/client-server-api/modules/room_previews.md

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---
type: module
weight: 170
---
### Room Previews
It is sometimes desirable to offer a preview of a room, where a user can
"lurk" and read messages posted to the room, without joining the room.
This can be particularly effective when combined with [Guest Access](#guest-access).
Previews are implemented via the `world_readable` [Room History
Visibility](#room-history-visibility). setting, along with a special version of the [GET
/events](#get_matrixclientr0events) endpoint.
#### Client behaviour
A client wishing to view a room without joining it should call [GET
/rooms/:room\_id/initialSync](#get_matrixclientr0roomsroomidinitialsync),
followed by [GET /events](#get_matrixclientr0events). Clients will need to do
this in parallel for each room they wish to view.
Clients can of course also call other endpoints such as [GET
/rooms/:room\_id/messages](#get_matrixclientr0roomsroomidmessages)
and [GET /search](#post_matrixclientr0search) to
access events outside the `/events` stream.
{{peeking\_events\_cs\_http\_api}}
#### Server behaviour
For clients which have not joined a room, servers are required to only
return events where the room state at the event had the
`m.room.history_visibility` state event present with
`history_visibility` value `world_readable`.
#### Security considerations
Clients may wish to display to their users that rooms which are
`world_readable` *may* be showing messages to non-joined users. There is
no way using this module to find out whether any non-joined guest users
*do* see events in the room, or to list or count any lurking users.