  The first measurements of anti-$k_{T}$ jet energy spectrum and substructure
in hadronic $Z$ decays are presented. The archived $e^+e^-$ annihilation data
at a center-of-mass energy of 91 GeV were collected with the ALEPH detector at
LEP in 1994. The jet substructure was analyzed as a function of jet energy. The
results are compared with the perturbative QCD calculations and predictions
from the PYTHIA v6.1, SHERPA, and HERWIG v7.1.5 event generators. In this note,
jet reconstruction procedure, jet energy calibration, and the performance with
archived ALEPH data and Monte Carlo simulations are also documented.
