About Tagged Netstrings

Far worse. As defined, you can't write a parser for "tagged netstrings" without:

* Infinite lookahead - the type for a tagged netstring doesn't appear until the END of up to 100 MB of contents.

* Large intermediate memory usage - a string of the form 9990:9985:9980:9975: <...> ]]]] may consume a very large amount of memory for substrings during parsing.

* An int() implementation which exactly matches Python's.

* Ambiguity.

Bencode (http://en.wikipedia.org/wiki/Bencode) has been around much longer, and is considerably better thought out. There's no reason to not just use that instead.