+1. While yes, you can have a giant json object, and you can hack your way around the obvious memory issues, it’s still a bad idea, imo. Even if you solve it for one use case in one language, you’ll have a bad time as soon as you use different tooling. JSON really is a universal message format, which is useful precisely because it’s so interoperable. And it’s only interoperable as long as messages are reasonably sized.

The only thing I miss from json lines is allowing a type specifier, so you can mix different types of messages. It’s not at all impossible to work around with wrapping or just roll a custom format, but still, it would be great to have a little bit of metadata for those use cases.

confusingly jq also has a streaming mode https://stedolan.github.io/jq/manual/#Streaming that streams JSON values as [<path>,<value>] pairs. This can also be combined with null input and enables one to reduce, foreach etc in a memory efficient way, eg sum all .a in an array without loading the whole array into memory:

    $ echo '[{"a":1},{"b":2},{"a":3}]' | jq -n --stream 'reduce (inputs | select(.[0][1:] == ["a"])[1]) as $v (0; .+$v)'
    4

Isn't this pretty much what JSON streaming does?