/* this function should perform module initialization and return success/error code */
int	zbx_module_init(void);

/* this function should return a list of custom checks supported by the module */
zbx_item_list_t		zbx_module_item_list(void);

/* this function should set timeout for item checks */
void	zbx_module_item_timeout(int timeout);

/* this function is optional and should free module resources if necessary */
int	zbx_module_uninit(void);

/* this is an example of a function performing custom check, returns success/error code */
int	zbx_module_custom_check(zbx_agent_request_t request, zbx_agent_result_t *result);

/* this defines the version of the header file, should be updated every time new functions are added to API (or old functions are removed) */
#define ZBX_MODULE_HEADER_VERSION	...

/* this function returns version of the library loaded in runtime */
int	zbx_module_library_version(void);

/* this type stores list of custom metrics */
typedef struct zbx_item_list	zbx_item_list_t;

/* this type stores a metric */
typedef struct zbx_metric	zbx_metric_t;

/* this type stores check request */
typedef struct zbx_agent_request	zbx_agent_request_t;

/* this type stores check result */
typedef struct zbx_agent_result	zbx_agent_result_t;

/* this function creates custom check list */
zbx_item_list_t	zbx_item_list_create(void);

/* this function appends custom check to the list */
void	zbx_item_list_append(zbx_item_list_t list, zbx_metric_t metric);

/* this function frees check list resources (Zabbix should make his own copy) */
void	zbx_item_list_destroy(zbx_item_list_t list);

/* this function creates custom check description */
zbx_metric_t	zbx_metric_create(void);

/* possible metric attributes */
#define ZBX_METRIC_ATTR_KEY ...
#define ZBX_METRIC_ATTR_ALLOW_PARAMS ...
/* list can be expanded without breaking compatibility */

/* this function sets custom check attributes */
int	zbx_metric_attr_set(int attribute, void *value);

/* this function frees custom check resources */
void	zbx_metric_destroy(zbx_metric_t);

/* similar functions to manipulate request and result */
...