Remember that the trust relationship in OpenPGP is not transitive. If you know that Alice's key is valid and you trust Alice, then if Alice signs Bob's key, you know that Bob's key is valid. However, unless you also personally trust Bob, then you cannot trust any signatures that Bob makes. (Unless Alice's signature also indicates trust in Bob; but this is not the common situation, think of e.g., keysigning parties.) Hence, if you have a path from you to Carol going through Alice and Bob, and you trust Alice but you do not know Bob, then you have no guarantees about the validity of Carol's key (Bob may have signed a phoney key).

Of course, checking paths in the Web of Trust is not entirely useless, because a key which is connected to you probably has more chances to be valid. However, it offers no strong guarantee on trust unless you personally trust all intermediates along that chain.

Another similar tool:

https://www.lysator.liu.se/~jc/wotsap/

Watch out, this sets random keys to ultimate trust.