An envelope opening tool comprising: a tool body having a slot extending through said body along an axis to pass through opposing first and second exterior faces (12a, 12b) of said body to define a channel having a first end at said first face and a second end at said second face, said channel being closed on three sides thereof around the axis by opposing first and second closed sides (20, 22) of the channel and a third closed side of said channel interconnecting the first and second closed sides thereof, leaving a fourth side of the channel open between the first and second closed sides of the channel at a position opposing the third closed side; and a blade mounted to the tool body in a position projecting into the channel from the first side thereof toward the opposing second to define a cutting edge positioned within the channel, the blade lying in a plane spaced away from the third closed side of the channel in a direction toward the fourth open side of the channel, and the cutting edge sloping obliquely away from the first closed side of the channel toward the opposing second closed side of the channel in a direction moving from the first end of the channel to the second end thereof; wherein the axis is perpendicular to the first and second exterior faces (12a, 12b) of the body; the plane in which the blade lies is parallel to the axis; the tool body has an elongated shape of greater length than width, the first and second closed sides of the channel being spaced apart along the length of the tool body and the third and fourth sides of the channel being spaced apart along the width of the tool body; a thickness of the tool body separates the first and second exterior faces thereof and is less than the width of the tool body; the closed third side of the channel is obliquely sloped relative to the first and exterior faces (12a, 12b) of the tool body such that the third closed side of channel is further from the plane in which the blade lies at the first end of the channel than at the second end of the channel; a gap between the second closed side of the channel and the cutting edge of the blade, at an end of said cutting edge closest to said second closed side of the channel, is between 19.05 and 31.75 micrometers (0.75 and 1.25 thousandths of an inch); and characterised in that a depth of the slot, measured from the open fourth side of the channel to the opposing closed third side of the channel, continuously decreases moving through the slot from the first end to the second end. a tool body having a slot extending through said body along an axis to pass through opposing first and second exterior faces (12a, 12b) of said body to define a channel having a first end at said first face and a second end at said second face, said channel being closed on three sides thereof around the axis by opposing first and second closed sides (20, 22) of the channel and a third closed side of said channel interconnecting the first and second closed sides thereof, leaving a fourth side of the channel open between the first and second closed sides of the channel at a position opposing the third closed side; and a blade mounted to the tool body in a position projecting into the channel from the first side thereof toward the opposing second to define a cutting edge positioned within the channel, the blade lying in a plane spaced away from the third closed side of the channel in a direction toward the fourth open side of the channel, and the cutting edge sloping obliquely away from the first closed side of the channel toward the opposing second closed side of the channel in a direction moving from the first end of the channel to the second end thereof; wherein the axis is perpendicular to the first and second exterior faces (12a, 12b) of the body; the plane in which the blade lies is parallel to the axis; the tool body has an elongated shape of greater length than width, the first and second closed sides of the channel being spaced apart along the length of the tool body and the third and fourth sides of the channel being spaced apart along the width of the tool body; a thickness of the tool body separates the first and second exterior faces thereof and is less than the width of the tool body; the closed third side of the channel is obliquely sloped relative to the first and exterior faces (12a, 12b) of the tool body such that the third closed side of channel is further from the plane in which the blade lies at the first end of the channel than at the second end of the channel; a gap between the second closed side of the channel and the cutting edge of the blade, at an end of said cutting edge closest to said second closed side of the channel, is between 19.05 and 31.75 micrometers (0.75 and 1.25 thousandths of an inch); and characterised in that a depth of the slot, measured from the open fourth side of the channel to the opposing closed third side of the channel, continuously decreases moving through the slot from the first end to the second end.