The interface of Chord exposes the Chord protocol by providing a callback function that notifies about nodes joining and leaving the neighborhood of a given node, and a function that calculates the successor when routing to a given node.

void event_register ((fn)(int));
ID next_hop (ID j, ID k);

On top of this interface, another interface is provided that stores and retrieves an item from a distributed hash table.

err_t insert (void *key, void *value);
void *lookup (void *key);