- for what platform(s) it is written (e.g. C code where tagged as 'Unix', that use Linux-isms)
- what the license is (home page claims 'free' or 'open source', source files mention license A, read me mentions license B)
- what the library does and, almost more importantly, what it's limitations are.
- what the dependencies of the library are.
- what systems the code has run on (it can for instance be useful to know that code has run in big-endian machines if your machine is big-endian)
The more of this info is present, the higher the probability that I will try to use your software.
There is lots of code out there where too little of this metadata is present. If such software is not solving some unique problem, I would prefer it if its writer did not make it available.