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We present the high-$z$ quasar candidate archive (HzQCA), summarizing thespectroscopic observations of 174 $z\gtrsim5$ quasar candidates usingKeck/LRIS, Keck/MOSFIRE, and Keck/NIRES. We identify 7 candidates as $z\sim 6$quasars 3 of them newly reported here, and 51 candidates as brown dwarfs. Inthe remaining sources, 74 candidates are unlikely to be quasars; 2 sources areinconclusive; the others could not be fully reduced or extracted. Based on theclassifications we investigate the distributions of quasars and contaminants incolor space with photometry measurements from DELS ($z$), VIKING/UKIDSS($YJHK_s$/$YJHK$), and un\textit{WISE} ($W1W2$). We find that the identifiedbrown dwarfs are not fully consistent with the empirical brown dwarf model thatis commonly used in quasar candidate selection methods. To refine spectroscopicconfirmation strategies, we simulate synthetic spectroscopy of high-$z$ quasarsand contaminants for all three instruments. The simulations utilize thespectroscopic data in HzQCA. We predict the required exposure times for quasarconfirmation and propose and optimal strategy for spectroscopic follow-upobservations. For example, we demonstrate that we can identify a $m_J=21.5$ at$z=7.6$ or a $m_J=23.0$ at $z=7.0$ within 15\,min of exposure time with LRIS.With the publication of the HzQCA we aim to provide guidance for future quasarsurveys and candidate classification.

High-$z$ Quasar Candidate Archive: A Spectroscopic Catalog of Quasars and Contaminants in Various Quasar Searches