| Name | Lines of code | Maintainability | Test coverage |
| opal/corelib/regexp.rb | 382 | A 3 hrs | |
| stdlib/native.rb | 454 | A 2 hrs | |
| stdlib/date.rb | 467 | C 1 day | |
| opal/corelib/kernel/format.rb | 488 | A 0 mins | |
| opal/corelib/string/unpack.rb | 603 | A 2 hrs | |
| opal/corelib/time.rb | 638 | D 1 day | |
| stdlib/matrix/eigenvalue_decomposition.rb | 652 | F 1 wk | |
| opal/corelib/module.rb | 660 | A 2 hrs | |
| opal/corelib/kernel.rb | 685 | B 4 hrs | |
| opal/corelib/hash.rb | 739 | A 2 hrs | |
| opal/corelib/number.rb | 783 | C 1 day | |
| opal/corelib/enumerable.rb | 976 | F 3 days | |
| stdlib/optparse.rb | 1,110 | F 1 wk | |
| stdlib/matrix.rb | 1,194 | F 4 days | |
| opal/corelib/string.rb | 1,595 | F 5 days | |
| opal/corelib/runtime.js | 2,000 | F 6 days | |
| opal/corelib/array.rb | 2,002 | F 1 wk |