The tantō's traditional overall length was 11.93 in (1 shaku, about 30 cm). The blade's length was about 5in to 12in (12 1/2 cm to 30 cm). Blades that were bigger (13 to 14 inches) were called ko-wakizashi, meaning "small short sword." The tantōs which varied from the traditional size were called O-tantō or Sunobi tantō.
The tantō was a weapon with a single-edged blade and a curved shape. It was designed for soft targets and was thought to be a hidden weapon of the samurai. It was extremely effective in close fighting.
The tantō appeared during the Heian Period (795-1192 A.D.) and developed as a weapon during the Kamakura Period (1192-1333 A.D.). At that time the tantō was not just a weapon but also a work of art. It was richly decorated using the most spread styles: hira-tsukuri and uchi-sori. Later, in the Nambokucho period (1336-1392 A.D), tantōs become longer than 15.75 inches (37 cm). Blades become thinner and broader and thus even more dangerous. Different styles developed and the shape changed. During the Muromachi Period (1336–1573 A.D.) the tantō becomes once more narrow-bladed.
By this time the quality of the blade was better. It was the time when professional smiths appeared and there were several styles of tantō making. The best known smiths were: Sukesada and Norimitsu (Bizen-den); Kanemoto and Kanesada (Mino-den); Muramasa and Masashige (Ise). The beginning of Edo period (1603-1867 A.D.) was a period of relative peace after Japanese unification and, although not so many were made, they were of good quality. The heat treated blade's edge (hamon) becomes more waved and so more beautiful.
A great number of tantōs were made in the last 700 to 800 years. Some of them were for civil use. Others were made especially for samurai. One of the classifications is based on the hand guard type:
- tantō with a guard called tsuba;
- tantō with an aikuchi style of guard;
- tantō with hamadashi style of guard.
The most popular of the three tantōs were aikuchi and hamadashi. This was because of the fact that these two types had a small guard and they were easier to hide and carry. The tantō was not widely used on the battlefield, so the guard was mostly unnecessary.
Other styles of tantō differed by the shape of the blade. The best known are:
- Hira-zukuri - with a flat, narrow and thick blade. This was designed for slashing and piercing blows.
- Shobu-zukuri - with a ridge line and with a blood groove.
- Moroha - a double edged and very rare tantō
- Kissaki-moroha-zukuri - with a very long and sharp point (o-kissaki)
- Kaikan - short tantō with small guards, usually carried by women.
When the tantō was used on the battlefield it was supposed to go through the armor of the opponent when he was close. The best tantōs for this were those with a long, narrow blade and with a thick spine. The blow was applied with the point directed under or through the armor. The tantō was usually carried in a wide cloth belt (obi) with the edge up and the handle turned to the right. In the samurai house the tantō was often placed with the wakizashi (short sword). Samurai women were taught to use the tantō in case they needed to defend themselves or, if violated, to take their own life.
It is also considered that tantōs of different type were used for suicide ritual (seppuku, also hara-kiri). Still, it was mainly used by women samurai whose suicidal ritual was to cut their own throat. The men samurai had a different ritual: they used a wakizashi sword for disembowelment.