This free online LESS compiler will generate the final CSS code using your provided LESS source. This tool is best suited for quick tests and for learning LESS. LESS command-line & GUI compilers are available and will probably be better suited for your needs in the long run.
The LESS compiler does NOT support @import instructions, since it introduces external dependencies that are hard to implement for a web-base application. As a workaround, I suggest you provide the compiler with a single LESS file and that you split it after you're done testing.