Or

    jq  . foo.json

jq is freaking awesome! It can do amazing stuff, it's like awk for JSON on steroids. Highly recommend reading the documentation: https://stedolan.github.io/jq/manual/

useless use of cat:

python3 -m json.tool foo.json

Usually though what happens is this:

    :) cat foo.json
    [oh crap]
    :) cat foo.json | python -m foo.tool

For the 2nd command I'd hit "[up] | pyth[tab] -m json.tool"