SRD v3.5

http://dndsrd.net/
https://srd.dndtools.org/

- RACES

https://srd.dndtools.org/srd/races/races.html

- CHARACTER CLASSES

https://srd.dndtools.org/srd/classes/classes.html

- FEAT INDEX

https://srd.dndtools.org/srd/tools/toolsFeatIndex.html

- VARIANT CLASSES, ALTERNATIVE CLASS FEATURES and SUBSTITUTION LEVELS

https://srd.dndtools.org/srd/variant/variantList.html

- PRESTIGE CLASSES

https://srd.dndtools.org/srd/classes/prestigeClasses.html

- CREATURE TEMPLATES

https://www.realmshelps.net/monsters/templates/index.shtml