Command-line JSON processor. Used in the talk as an analogy for what EQL does: a pearl-like string notation for traversing and selecting data from nested structures. jq supports selection and traversal but, as far as the speaker could find from the tutorial, lacks a clear notation for derivations (e.g. concatenating a base URL with an id to form a full URL). Cited as the inspiration-by-contrast for why EQL uses data structures rather than a string notation, so queries can be manipulated programmatically.