Scientific Calculator covers what a physical scientific calculator does, trig functions, logarithms, powers and roots, factorials, and memory, with both a button grid and direct keyboard typing.
The basic operators (+, -, ×, ÷, ^ for powers), parentheses, factorial (!), percent, sin/cos/tan and their inverses, log (base 10), ln (natural log), square root, absolute value, and the constants pi and e.
Trig functions interpret their input differently depending on the angle unit. sin(90) means something different in degrees versus radians, so switching modes changes the result for any expression using sin, cos, tan, or their inverses.
Yes, the display is a normal text field. Type something like sqrt(16)+2^3 directly and press Enter. The buttons are there for convenience, not a requirement.
No. Every calculation runs locally in your browser using a small expression parser. Nothing you type is sent to a server.