  The completeness of source detection is critical for analyzing the
photometric and spatial properties of the population of interest observed by
astronomical imaging. We present a software package $\mathtt{ComEst}$, which
calculates the completeness of source detection on charge-coupled device (CCD)
images of astronomical observations, especially for the optical and
near-infrared (NIR) imaging of galaxies and point sources. The completeness
estimator $\mathtt{ComEst}$ is designed for the source finder
$\mathtt{SExtractor}$ used on the CCD images saved in the Flexible Image
Transport System (FITS) format. Specifically, $\mathtt{ComEst}$ estimates the
completeness of the source detection by deriving the detection rate of
synthetic point sources and galaxies simulated on the observed CCD images. In
order to capture any observational artifacts or noise properties while deriving
the completeness, $\mathtt{ComEst}$ directly carries out the detection of
simulated sources on the observed images. Given an observed CCD image saved in
FITS format, $\mathtt{ComEst}$ derives the completeness of the source detection
from end to end as a function of source flux (or magnitude) and CCD position.
In addition, $\mathtt{ComEst}$ can also estimate the purity of the source
detection by comparing the catalog of the detected sources to the input
catalogs of the simulated sources. We run ComEst on the images from Blanco
Cosmology Survey (BCS) and compare the derived completeness as a function of
magnitude to the limiting magnitudes derived by using the Signal-to-Noise ratio
(SNR) and number count histogram of the detected sources. $\mathtt{ComEst}$ is
released as a Python package with an easy-to-use syntax and is publicly
available at https://github.com/inonchiu/ComEst
