Both entrance exams are high level exams. Both GARTE and CAT are available for master degree programs. Gate contains aptitude, Numerical and verbal ability questions.

GATE is provides admission for M.Tech course and CAT is provides admission for management course.

GATE is added with its the engineering syllabus and to get into IITs there are only a handful of seats is GATE for enter for M.Tech.

I think GATE is much tuff than CAT

Common Admission Test is an all-India entrance examination conducted by the Indian Institutes of Management for getting admission to the postgraduate courses in management courses of several management institutes all over India including the Indian Institute of Managements (IIM).

Eligibility:
Candidates must have a graduation degree with minimum of 50% marks (45% in the case of reserved categories).

Graduate Aptitude Test Engineering is an all India entrance Examination, which is conducted jointly by IISc and IITs.
On the basis of the GATE score, one can take admissions to Postgraduate Programmes in IISc, IITs and other Universities in India.

Eligibility:
Candidates having a bachelor’s degree in Engineering/ Technology/ Architecture or Master’s degree in any branch of Science/ Mathematics/ Statistics/ Computer Applications can appear for GATE.