how Openstreetmap validate the input? Does any tool do the validation before uploading the data?

There are a fe ways to answer this questions :

• The editors do a fair bit of validation before upload. JOSM's validator in particular is quite powerfull.
• The editors also try hard to prevent bad edits in the first place (like iD's polygon tool avoids creating an unclosed building way).
• The api doesn't do any validation beyond making sure the request is well-formed, and stores the result directly (old versions of the data are kept).
• There are many Quality Assurance tools to check the data once it is uploaded.
• Many mappers keep an eye on their favorite areas to fix problems as they occur.

See previous questions tagged "quality". E.g. data-verification-process! The answers there answer your question (although not really focussing on the "before" aspect).