"It's too soon to tell if the project will be successful."
In this sentence 'too' is a/an-

• "It's too soon to tell if the project will be successful."
- In this sentence 'too' is an- adverb

• Too (adverb of degree, modifying adjective(s) and adverb(s)
- English Meaning: to a higher degree than is desirable, permissible, or possible; excessively.
- Bangla Meaning: অত্যন্ত বেশি পরিমাণে; প্রয়োজনের তুলনায় বেশি পরিমাণে।
- যেমন: He is too weak to walk.

• প্রশ্নে উল্লিখিত বাক্যে too, soon এর পূর্বে বসে একে modify করছে।
- In this sentence, 'too' modifies the adverb 'soon', indicating an excessive or inappropriate degree of earliness. 
- too সাধারণত adverb হিসেবেই বাক্যে ব্যবহৃত হয়।

Source:
1. Oxford Learner's Dictionary. 
2. Accessible Dictionary by Bangla Academy.