The ${\mathrm{𝔰𝔩}}_3$ polynomial is a quantum invariant for knots. It has been categorified by Khovanov in 2004 in a TQFT fashion. The natural way to extend this categorification to an invariant of tangle is construct a $0+1+1$ TQFT. From this construction emerge some algebras called Khovanov-Kuperberg algebras (or ${\mathrm{𝔰𝔩}}_3$-web algebras) and some particular projective modules called web-modules over these algebras. I will give a combinatorial caracterisation of indecomposable web-modules.