When coupling tubular parts by fitting, the seal interposed between them may roll on itself, be pinched or damaged. Now, a twisted or damaged seal no longer correctly ensures the seal-tightness and it is very difficult to detect this. The present application discloses a tool for installing a seal between two tubular parts, one male and one female, including a compression ring to encircle the male part and exert a compression on the seal before producing the join. The tool also includes a tongue that can be positioned at a chamfered surface of the female tubular part. The tongue makes it possible to offer the pre-compressed seal with the dimensions of the female part a continuous travel making it possible to prevent any twisting or other effect compromising the seal-tightness.