To visit Costa Rica you need:

1) A passport that is valid for at least 6 months after the entry date to Costa Rica.

2) A prepaid airline ticket to leave Costa Rica within 90 days of your arrival.
If your passport is from the United States, Canada, mostly any country in Europe, you don’t need a visa. Please visit the Costa Rican embassy page for more details.

If you have visited any of the following countries previously to your trip to Costa Rica, you’re required to present evidence of a yellow fever vaccination:

Angola, Benin, Bolivia, Brazil, Burkina Faso, Cameroon, Colombia, Democratic Republic of Congo, Ecuador, French Guyana, Gabon, Gambia Ghana, Guinea, Liberia, Nigeria, Peru, Sierra Leone, Sudan and Venezuela.

If you have any concerns regarding health and diseases, check out the CDC website.