The mtools tool is a collection of helper scripts developed by MongoDB engineers to parse and filter MongoDB log files, visualize information from log files, and set up complex MongoDB test environments on a local machine. The tool consists of five individual scripts: mloginfo, mlogfilter, mplotqueries, mlogvis, and mlaunch. mloginfo provides general information about the contents of log files, while mlogfilter helps narrow down searches in log files by filtering on attributes such as namespace, type of operation, or connection. The mplotqueries script presents information from log files visually in various ways, including scatter plots, histograms, event and range plots, and other specialized graphs. mlogvis is a web-based alternative to mplotqueries using the d3.js JavaScript visualization library. Mlaunch spins up any number of MongoDB nodes on a local machine, either as a stand-alone or as part of a replica set or sharded cluster. The tool can be used to diagnose system issues, optimize queries and indexes, visualize log files, and reproduce issues locally. It is open-source and available for download on GitHub and PyPI.