This is a pretty low use api (as you’d normally have the database anyway), but it’s one that’s not directly provided by CCP:
Typename to typeid. json and xml output.
http://www.fuzzwork.co.uk/api/typeid.php?typename=Tritanium
http://www.fuzzwork.co.uk/api/typeid.php?typename=Tritanium&format=xml
If you want to pass in multiple names, then use a pipe delimiter to split them up, and use a slightly different url. (I didn’t want to mess with anyone already using the json format.
https://www.fuzzwork.co.uk/api/typeid2.php?typename=Tritanium|Pyerite&format=xml
https://www.fuzzwork.co.uk/api/typeid2.php?typename=Tritanium|Pyerite