Adding paid links to media captions in a social networking system

A non-transitory computer readable storage medium storing computer program instructions, the instructions when executed by a processor causing the processor to:

• provide a posting interface to a posting user of an online system to post content for distribution to users in a newsfeed of the online system, the posting interface providing an interface element for a media content item and a space for the posting user to enter a caption for describing the media content item, the caption configured to receive a textual input;
• receive a media content item from the posting user of the online system, the media content item comprising an image or a video and associated with a caption including text content;
• identify a substring of the caption indicative of a web address, wherein the substring is a portion of a link text, and the link text is a portion less than all of the caption input by the posting user;
• responsive to identifying the substring, identify a remaining portion of the link text including additional character adjacent to the substring until a next character space;
• prompt the posting user to pay a fee in exchange for generating a link based on the link text;
• responsive to receiving payment of the fee from the posting user, generate the link within the caption, the generated link comprising a selectable object within the caption that when activated by a client device causes the client device to access a digital location specified by the address;
• and
• receive a request for newsfeed content from another user connected to the posting user;
• rank the media content item with other content items provided by connections of the other user, the ranking based on the other user's interactions with content in the online system;
• select the media content item based on the ranking for presentation to the other user in the newsfeed;
• and
• send the media content item and caption for display to the other user in a newsfeed of content items.