diff --git a/src/bdberl.erl b/src/bdberl.erl
index 56f502a..941bf41 100644
--- a/src/bdberl.erl
+++ b/src/bdberl.erl
@@ -29,10 +29,31 @@
 
 -define(is_lock_error(Error), (Error =:= deadlock orelse Error =:= lock_not_granted)).
 
+-type db() :: non_neg_integer().
+-type db_type() :: btree | hash.
+-type db_flags() :: [atom()].
+-type db_key() :: term().
+-type db_value() :: term().
+-type db_ret_value() :: not_found | db_value().
+
+-type error_reason() :: term().
+-type error() :: {error, error_reason()}.
+
+-type txn_fun_ret() :: abort | term().
+-type txn_fun() :: fun(() -> txn_fun_ret()).
+-type txn_retries() :: infinity | non_neg_integer().
+
+-type db_update_fun() :: fun((db_key(), db_value(), any()) -> db_value()).
+
+
+-spec open(Name :: nonempty_string(), Type :: db_type()) -> db().
 
 open(Name, Type) ->
     open(Name, Type, [create]).
 
+
+-spec open(Name :: nonempty_string(), Type :: db_type(), Opts :: db_flags()) -> db().
+
 open(Name, Type, Opts) ->
     %% Map database type into an integer code
     case Type of
@@ -48,9 +69,15 @@ open(Name, Type, Opts) ->
             {error, Errno}
     end.
 
+
+-spec close(Db :: db()) -> ok | error().
+
 close(Db) ->
     close(Db, []).
 
+
+-spec close(Db :: db(), Opts :: db_flags()) -> ok | error().
+
 close(Db, Opts) ->
     Flags = process_flags(Opts),
     Cmd = <<Db:32/signed-native, Flags:32/native>>,
@@ -62,9 +89,15 @@ close(Db, Opts) ->
             {error, Reason}
     end.
 
+
+-spec txn_begin() -> ok | error().
+
 txn_begin() ->
     txn_begin([]).
 
+
+-spec txn_begin(Opts :: db_flags()) -> ok | error().
+
 txn_begin(Opts) ->
     Flags = process_flags(Opts),
     Cmd = <<Flags:32/native>>,
@@ -74,9 +107,15 @@ txn_begin(Opts) ->
         Error -> {error, {txn_begin, Error}}
     end.
 
+
+-spec txn_commit() -> ok | error().
+
 txn_commit() ->
     txn_commit([]).
 
+
+-spec txn_commit(Opts :: db_flags()) -> ok | error().
+
 txn_commit(Opts) ->
     Flags = process_flags(Opts),
     Cmd = <<Flags:32/native>>,
@@ -91,6 +130,9 @@ txn_commit(Opts) ->
             {error, {txn_commit, Error}}
     end.
 
+
+-spec txn_abort() -> ok | error().
+
 txn_abort() ->
     <<Result:32/signed-native>> = erlang:port_control(get_port(), ?CMD_TXN_ABORT, <<>>),
     case decode_rc(Result) of
@@ -103,9 +145,16 @@ txn_abort() ->
             {error, {txn_abort, Error}}
     end.
 
+
+-spec transaction(Fun :: txn_fun()) -> {ok, db_value()} | {error, error()}.
+
 transaction(Fun) ->
     transaction(Fun, infinity).
 
+
+-spec transaction(Fun :: txn_fun(), Retries :: txn_retries()) ->
+    {ok, db_value()} | {error, error()}.
+
 transaction(_Fun, 0) ->
     txn_abort(),
     {error, {transaction_failed, retry_limit_reached}};
@@ -141,39 +190,79 @@ transaction(Fun, Retries) ->
             Error
     end.
 
+
+-spec put(Db :: db(), Key :: db_key(), Value :: db_value()) ->
+    ok | {error, error()}.
+
 put(Db, Key, Value) ->
     put(Db, Key, Value, []).
 
+
+-spec put(Db :: db(), Key :: db_key(), Value :: db_value(), Opts :: db_flags()) ->
+    ok | {error, error()}.
+
 put(Db, Key, Value, Opts) ->
     do_put(?CMD_PUT, Db, Key, Value, Opts).
 
+
+-spec put_r(Db :: db(), Key :: db_key(), Value :: db_value()) ->
+    ok | {error, error()}.
+
 put_r(Db, Key, Value) ->
     put_r(Db, Key, Value, []).
 
+
+-spec put_r(Db :: db(), Key :: db_key(), Value :: db_value(), Opts :: db_flags()) ->
+    ok | {error, error()}.
+
 put_r(Db, Key, Value, Opts) ->
     case put(Db, Key, Value, Opts) of
         ok -> ok;
         Error -> throw(Error)
     end.
 
+
+-spec put_commit(Db :: db(), Key :: db_key(), Value :: db_value()) ->
+    ok | {error, error()}.
+
 put_commit(Db, Key, Value) ->
     put_commit(Db, Key, Value, []).
 
+
+-spec put_commit(Db :: db(), Key :: db_key(), Value :: db_value(), Opts :: db_flags()) ->
+    ok | {error, error()}.
+
 put_commit(Db, Key, Value, Opts) ->
     do_put(?CMD_PUT_COMMIT, Db, Key, Value, Opts).
 
+
+-spec put_commit_r(Db :: db(), Key :: db_key(), Value :: db_value()) ->
+    ok | {error, error()}.
+
 put_commit_r(Db, Key, Value) ->
     put_commit_r(Db, Key, Value, []).
 
+
+-spec put_commit_r(Db :: db(), Key :: db_key(), Value :: db_value(), Opts :: db_flags()) ->
+    ok | {error, error()}.
+
 put_commit_r(Db, Key, Value, Opts) ->
     case do_put(?CMD_PUT_COMMIT, Db, Key, Value, Opts) of
         ok -> ok;
         Error -> throw(Error)
     end.
 
+
+-spec get(Db :: db(), Key :: db_key()) ->
+    {ok, db_ret_value()} | {error, error()}.
+
 get(Db, Key) ->
     get(Db, Key, []).
 
+
+-spec get(Db :: db(), Key :: db_key(), Opts :: db_flags()) ->
+    {ok, db_ret_value()} | {error, error()}.
+
 get(Db, Key, Opts) ->
     {KeyLen, KeyBin} = to_binary(Key),
     Flags = process_flags(Opts),
@@ -190,9 +279,16 @@ get(Db, Key, Opts) ->
             {error, {get, decode_rc(Error)}}
     end.
 
+-spec get_r(Db :: db(), Key :: db_key()) ->
+    {ok, db_ret_value()} | {error, error()}.
+
 get_r(Db, Key) ->
     get_r(Db, Key, []).
 
+
+-spec get_r(Db :: db(), Key :: db_key(), Opts :: db_flags()) ->
+    {ok, db_ret_value()} | {error, error()}.
+
 get_r(Db, Key, Opts) ->
     case get(Db, Key, Opts) of
         {ok, Value} -> {ok, Value};
@@ -200,9 +296,17 @@ get_r(Db, Key, Opts) ->
         Error       -> throw(Error)
     end.
 
+
+-spec update(Db :: db(), Key :: db_key(), Fun :: db_update_fun()) ->
+    {ok, db_value()} | {error, error()}.
+
 update(Db, Key, Fun) ->
     update(Db, Key, Fun, undefined).
 
+
+-spec update(Db :: db(), Key :: db_key(), Fun :: db_update_fun(), Args :: [any()]) ->
+    {ok, db_value()} | {error, error()}.
+
 update(Db, Key, Fun, Args) ->
     F = fun() ->
             Value = case get_r(Db, Key, [rmw]) of
@@ -218,9 +322,15 @@ update(Db, Key, Fun, Args) ->
         end,
     transaction(F).
 
+
+-spec truncate() -> ok | {error, error()}.
+
 truncate() ->
     truncate(-1).
 
+
+-spec truncate(Db :: db()) -> ok | {error, error()}.
+
 truncate(Db) ->
     Cmd = <<Db:32/signed-native>>,
     <<Result:32/signed-native>> = erlang:port_control(get_port(), ?CMD_TRUNCATE, Cmd),
@@ -235,6 +345,9 @@ truncate(Db) ->
             {error, {truncate, decode_rc(Error)}}
     end.
 
+
+-spec cursor_open(Db :: db()) -> ok | {error, error()}.
+
 cursor_open(Db) ->
     Cmd = <<Db:32/signed-native, 0:32/native>>,
     <<Rc:32/signed-native>> = erlang:port_control(get_port(), ?CMD_CURSOR_OPEN, Cmd),
@@ -246,15 +359,26 @@ cursor_open(Db) ->
     end.
 
 
+-spec cursor_next() -> ok | {error, error()}.
+
 cursor_next() ->
     do_cursor_move(?CMD_CURSOR_NEXT).
 
+
+-spec cursor_prev() -> ok | {error, error()}.
+
 cursor_prev() ->
     do_cursor_move(?CMD_CURSOR_PREV).
 
+
+-spec cursor_current() -> ok | {error, error()}.
+
 cursor_current() ->
     do_cursor_move(?CMD_CURSOR_CURR).
 
+
+-spec cursor_close() -> ok | {error, error()}.
+
 cursor_close() ->
     <<Rc:32/signed-native>> = erlang:port_control(get_port(), ?CMD_CURSOR_CLOSE, <<>>),
     case decode_rc(Rc) of
@@ -264,6 +388,10 @@ cursor_close() ->
             {error, Reason}
     end.
 
+
+-spec delete_database(Filename :: nonempty_string()) ->
+    ok | {error, error()}.
+
 delete_database(Filename) ->
     Cmd = <<(list_to_binary(Filename))/binary, 0:8>>,
     <<Rc:32/signed-native>> = erlang:port_control(get_port(), ?CMD_REMOVE_DB, Cmd),
@@ -275,6 +403,8 @@ delete_database(Filename) ->
     end.
 
 
+-spec get_data_dirs() -> [nonempty_string(),...] | {error, error()}.
+
 get_data_dirs() ->
     %% Call into the BDB library and get a list of configured data directories
     Cmd = <<?SYSP_DATA_DIR_GET:32/signed-native>>,
@@ -293,6 +423,10 @@ get_data_dirs() ->
             {error, Reason}
     end.
 
+
+-spec get_cache_size() ->
+    {ok, non_neg_integer(), non_neg_integer(), non_neg_integer()} | {error, error()}.
+
 get_cache_size() ->
     Cmd = <<?SYSP_CACHESIZE_GET:32/signed-native>>,
     <<Result:32/signed-native, Gbytes:32/native, Bytes:32/native, Ncaches:32/native>> =
@@ -304,6 +438,9 @@ get_cache_size() ->
             {error, Result}
     end.
 
+
+-spec get_txn_timeout() -> {ok, timeout()} | {error, error()}.
+
 get_txn_timeout() ->
     Cmd = <<?SYSP_TXN_TIMEOUT_GET:32/signed-native>>,
     <<Result:32/signed-native, Timeout:32/native>> = erlang:port_control(get_port(), ?CMD_GETINFO, Cmd),