Is hydrolysis exothermic or endothermic?

It depends on the particular reaction.

Two points to remember:

• Breaking of bonds is always endothermic.
• Formation of bonds is always exothermic.

Consider the hydrolysis of an ester:

##"RCOOR"_1 + "HOH" → "RCOOH" + "R"_1"OH"##

We could consider this simplistically as the breaking of two old bonds and the formation of two new bonds.

##underbrace("RCO-OR"_1)_color(red)("break C-O bond") + underbrace("H-OH")_color(red)("break O-H bond") → underbrace("RCO-OH")_color(red)("form new C-O bond") + underbrace("R"_1"O-H")_color(red)("form new O-H bond")##

The energy terms for breaking and forming the ##"C-O"## and ##"O-H"## bonds will be similar but not identical

Probably of more importance are the relative stabilities of the products and the reactants.

If a product is much more stable than a reactant because of resonance, inductive, steric, or solvation effects, the hydrolysis will almost certainly be exothermic.