A well tool system for performing an operation in an oil/gas well, wherein the well tool system comprises: a well tool ; a bore comprising a lock groove ; wherein the well tool comprises: - a mandrel having a longitudinal direction (I-I) and a radial direction (R) perpendicular to the longitudinal direction ( I-I ); and - an anchoring device for longitudinally locking the well tool to the lock groove of the bore ; wherein the anchoring device comprises: - a first ring arranged radially outside the mandrel ; - a second ring arranged radially outside the mandrel at a longitudinal distance from the first ring and movable in the longitudinal direction ( I-I ) relative to the first ring ; - a spring element being substantially ring-shaped and arranged radially outside the mandrel ; and - a plurality of locking dogs distributed circumferentially on the spring element and located longitudinally between the first ring and the second ring , the plurality of locking dogs being designed to be engaged into the lock groove of the bore ; wherein the anchoring device has a run state in which the first ring and the second ring are provided at an initial longitudinal distance ( D R ) from each other; and wherein the anchoring device has a set state in which the first ring and the second ring are provided at a shorter distance ( D S ) from each other, thereby wedging the locking dogs outwards in the radial direction ( R ); wherein the spring element is configured to bias the locking dogs inwards in the radial direction ( R ) towards the run state of the anchoring device . a well tool ; a bore comprising a lock groove ; wherein the well tool comprises: - a mandrel having a longitudinal direction (I-I) and a radial direction (R) perpendicular to the longitudinal direction ( I-I ); and - an anchoring device for longitudinally locking the well tool to the lock groove of the bore ; - a mandrel having a longitudinal direction (I-I) and a radial direction (R) perpendicular to the longitudinal direction ( I-I ); and - an anchoring device for longitudinally locking the well tool to the lock groove of the bore ; wherein the anchoring device comprises: - a first ring arranged radially outside the mandrel ; - a second ring arranged radially outside the mandrel at a longitudinal distance from the first ring and movable in the longitudinal direction ( I-I ) relative to the first ring ; - a spring element being substantially ring-shaped and arranged radially outside the mandrel ; and - a plurality of locking dogs distributed circumferentially on the spring element and located longitudinally between the first ring and the second ring , the plurality of locking dogs being designed to be engaged into the lock groove of the bore ; - a first ring arranged radially outside the mandrel ; - a second ring arranged radially outside the mandrel at a longitudinal distance from the first ring and movable in the longitudinal direction ( I-I ) relative to the first ring ; - a spring element being substantially ring-shaped and arranged radially outside the mandrel ; and - a plurality of locking dogs distributed circumferentially on the spring element and located longitudinally between the first ring and the second ring , the plurality of locking dogs being designed to be engaged into the lock groove of the bore ; wherein the anchoring device has a run state in which the first ring and the second ring are provided at an initial longitudinal distance ( D R ) from each other; and wherein the anchoring device has a set state in which the first ring and the second ring are provided at a shorter distance ( D S ) from each other, thereby wedging the locking dogs outwards in the radial direction ( R ); wherein the spring element is configured to bias the locking dogs inwards in the radial direction ( R ) towards the run state of the anchoring device . <EOS>