When talking about troubleshooting Oracle issues I sometime find myself in conversations like “I’ve this problem ABC and I’m trying to understand what’s happening” so at that point I jump in and ask “why didn’t you use [tool XYZ|script 123|etc] ?”… well the answer is usually “I didn’t even know it existed, where can I find it? why is it not advertised anywhere?”

That’s why for my first post I decided to make a list of the tools available on MOS that I usually use and where to find them.
They are all free to download and use, you just need a valid MOS account

SQLTXPLAIN (SQLT) – *THE* tool when it comes to SQL Tuning… and not only
SQLHC – A reduced version of SQLT focused on Health-Checks… and more
MVHC – A set of Health-Checks focused on the good health of your Mviews
PXHC – A set of Health-Checks focused on the Parallel Execution setup/configuraton
VERSION_RPT – A script to collect and format info from V$SQL_SHARED_CURSOR
PROCWATCHER – A tool to monitor and examine Oracle and Clusterware processes at an interval

There are some other great tools I have in my swiss-knife directory that are not coming from MOS like EDB360 and Snapper.
I suggest you google them and make sure to have them ready!