Check it, query DuckDuckGo for roll 3d12+4 (https://duckduckgo.com/?q=roll+3d12+%2B+4) (just below the search input box, above the sponsored link)
It rolls dice for you!
It even supports irregular dice such as 3d19+7. It doesn't support multiple dice (yet) like 1d4+3d6+10
Checking the source code (because yes, DDG is open source) I discovered it also supports another strange format for dice rolling:
roll 4d6 - L (https://duckduckgo.com/?q=roll+4d6-L)
Which I first assumed would roll 4d6 and discard the lowest, like you sometimes do to generate stats for D&D characters, but instead it rolls 4d6, adds them except for the lowest, which it subtracts from the total. Try it out. There is also a format for 3d6-H which subtracts the highest value instead of adding it.
Anyone know what game system such dice rules are used for? I'm curious.
This is the distribution for 4d6-L:
0 | 0.0 %
1 | 0.0 %
2 | 0.1 %
3 | 0.3 %
4 | 0.9 % ==
5 | 1.9 % ====
6 | 3.5 % ========
7 | 5.9 % ==============
8 | 8.9 % ======================
9 | 12.1 % ==============================
10 | 14.6 % ====================================
11 | 15.8 % =======================================
12 | 14.7 % ====================================
13 | 10.8 % ==========================
14 | 6.2 % ===============
15 | 3.1 % =======
16 | 1.2 % ===
17 | 0.3 %