Board Thread:Questions and Answers/@comment-24.102.250.77-20200413025117/@comment-25364614-20200414120122

You'll only find light novel purists here. lol. So its light novels if you want don't want to miss out on all of the details.

That said, the Index manga adaptation is highly praised by novel readers due to the artist. Reading it alongside the novels is fine even if some things are switched around or skipped and some details are lost.

Railgun is manga only (excluding the side story novels). Accelerator, Astral Buddy and Dark Matter are also manga only.