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An appropriate directory search tool?

The "MATE Search Tool" comes close.

It can:
  Select a starting directory.
  Search for a specific extension.
  Search for a keyword in file content.

It cannot:
   Search ONLY the specified directory.
   Return files that DO NOT contain a keyword.

I suspect what I want would most likely be what I'm looking for.
"ls" can search by extension and stay in specified directory.
It cannot include/exclude keywords.

My immediate problem involves only a couple dozen files so manual search is feasible.