As the title says. To put the contributions (explicitly) on the abstract:
- Is considered good practice
- Irrelevant as long as you correctly describe your paper? Source Research Guides
- No, explicitly mentioning the contributions is not considered good practice and should be avoided.
Here is an example of a paper I published on ArXiv. Would you say that the abstract is Ok? Please see I put the main emphasis on the contribution (I use the contribution as an excuse to then explain all the work done).
NOTE: Please don't confuse with the contribution of each author to the article! An article should have something new, therefore we can say a contribution to science. Some article's have a specific section for that reference. Others just mention it reference but my question goes if it is good to mention it in the abstract or not.
As this question is somewhat subjective and there might not be a CORRECT response. If after some time I consider fit there is not a precise justification (some indisputable reference for example) I will mark as a solution the response that had more upvotes, supposing the upvotes reflect what the community thinks.