CJ in MPLS
Make sure you indicate on your customs declaration that your tools are temporary imports (to Costa Rica) under HTS 9801.00.85 which covers: Professional books, implements, instruments & tools of trade, occupation or employment returned US by person after use temporarily abroad. The duty in the US is free and I expect it is also free in CR. If, upon looking up the import duties in CR, you determine that you would have to pay import duties, look into purchasing a carnet that would allow for temporary importation with the suspension of all import duties. You will pay if you end up leaving the tools behind however.
This only applies if you bring a lot of tools as a a few hand tools in a case can probably be claimed as personal items, i.e. not declared.
BTW, legal advice from the internet is probably worth less that what you would pay to import your tools to CR.