A jarring tool is disclosed. The tool has a segment of sub housing containing an upper stop proximate a first end thereof. An outer latch piece is connected to an upper end of the lower shaft inside the sub housing, and an upper shaft passes through the stop and connects on a first end thereof to an inner latch piece. A cap is on a second end of the upper shaft retaining a washer stack against the upper stop. A retainer is inside the sub housing and has an first piece providing a restraining region and an open region and a second piece attached to the sub housing. The retainer retains the inner and outer latch pieces in a latched position in the restraining region until the latch pieces are displaced toward the second end of the sub housing through the retainer to the open region as a result of a tensile force on the outer latch piece.