Does anyone know what conditions there are for adding a new coin to existing exchanges?
Is there some information gathered together?
Or the only way is sending requests to each stock exchange?
I believe you have to inquire as each exchange has different requirements. It's much easier to get listed on the lower level exchanges. If you pay a fee you probably just need to prove the coin is viable and free from malware. The higher level exchanges will need to be convinced that there is enough demand to make the extra overhead financially worthwhile for them.
