It depends. If you are reading it from an official source that offers it for free, such as a legitimate library e - book service or an official publisher's promotional offer, then it is legal. However, if you are using unauthorized or pirated websites, it is not legal.
In general, it's only legal to read the Spice and Wolf light novel for free if it is provided through legal means. There are some legal e - book services that might have it available for free borrowing or reading. But if you're getting it from a website that doesn't have the proper rights to distribute it, it's illegal. This is because the author and publisher own the rights to the work and should be compensated for its use, unless they choose to offer it for free through official channels.
Reading Spice and Wolf free online from legitimate channels is legal. For instance, if the author or publisher themselves have made certain parts available for free on their official website to attract readers or for promotional purposes. But accessing it through unlicensed platforms that are just hosting it without permission is a violation of copyright laws. So, always make sure to use proper and legal sources.