We derive exact bounds for the ${K}_{l3}$ decay form factors ${f}_{\ifmmode\pm\else\textpm\fi{}}(t)$. Particularly, we find the bound $({{m}_{K}}^{2}\ensuremath{-}{{m}_{\ensuremath{\pi}}}^{2})|{f}_{+}(0)|\ensuremath{\le}16{[\frac{1}{3}\ensuremath{\pi}\ensuremath{\Delta}(0)]}^{\frac{1}{2}}{({m}_{K}+{m}_{\ensuremath{\pi}})}^{\frac{1}{2}}{({{m}_{K}}^{\frac{1}{2}}+{{m}_{\ensuremath{\pi}}}^{\frac{1}{2}})}^{\ensuremath{-}1}$, where $\ensuremath{\Delta}(0)$ is the propagator of the divergence of the strangeness-changing current at zero momentum. If we further assume the Hamiltonian of Gell-Mann, Oakes, and Renner in order to estimate $\ensuremath{\Delta}(0)$, we obtain $|{f}_{+}(0)|\ensuremath{\lesssim}1.0$. Similarly, an inequality testing the standard ${K}_{l3}$ soft-pion theorem is found to be well satisfied. In addition, a new inequality involving derivatives of ${f}_{+}(t)$ is derived. Taking ${\ensuremath{\lambda}}_{+}\ensuremath{\sim}0.02$, this inequality leads to $|{f}_{\ensuremath{-}}(0)|\ensuremath{\lesssim}0.33$.