A method comprising: adding a content item at a client device, the content item being associated with a user account of a content management system; determining, via a client application at the client device, that either: the content item does not have a unique identifier from the content management system, the client application being associated with the content management system; obtaining the unique identifier for the content item, the unique identifier being defined by the content management system; or: the content item has a unique identifier from the content management system; when the content item has a unique identifier, sending, by the client application to the content management system, a request to verify a uniqueness of the unique identifier at the content management system, wherein the unique identifier is independent of namespaces at the content management system, wherein the content management system comprises namespaces that encompass a respective directory structure defined by respective user accounts, including the user account; based on the request, determining, by the client application, whether the unique identifier is verifiably unique at the content management system; when the unique identifier is verifiably unique at the content management system: adding a node representing the content item to a local tree at the client device, the node comprising the unique identifier and the local tree representing a filesystem state at the client device for content items associated with the user account; and uploading the content item with the unique identifier to the content management system; when the unique identifier is not verifiably unique at the content management system, obtaining a new unique identifier for the content item. adding a content item at a client device, the content item being associated with a user account of a content management system; determining, via a client application at the client device, that either: the content item does not have a unique identifier from the content management system, the client application being associated with the content management system; obtaining the unique identifier for the content item, the unique identifier being defined by the content management system; or: the content item has a unique identifier from the content management system; the content item does not have a unique identifier from the content management system, the client application being associated with the content management system; obtaining the unique identifier for the content item, the unique identifier being defined by the content management system; or: the content item has a unique identifier from the content management system; when the content item has a unique identifier, sending, by the client application to the content management system, a request to verify a uniqueness of the unique identifier at the content management system, wherein the unique identifier is independent of namespaces at the content management system, wherein the content management system comprises namespaces that encompass a respective directory structure defined by respective user accounts, including the user account; based on the request, determining, by the client application, whether the unique identifier is verifiably unique at the content management system; when the unique identifier is verifiably unique at the content management system: adding a node representing the content item to a local tree at the client device, the node comprising the unique identifier and the local tree representing a filesystem state at the client device for content items associated with the user account; and uploading the content item with the unique identifier to the content management system; adding a node representing the content item to a local tree at the client device, the node comprising the unique identifier and the local tree representing a filesystem state at the client device for content items associated with the user account; and uploading the content item with the unique identifier to the content management system; when the unique identifier is not verifiably unique at the content management system, obtaining a new unique identifier for the content item.