To find the output of the function \( y = -3x - 7 \) when the input is \( x = -5 \), we can plug in \(-5\) for \(x\):
\[
y = -3(-5) - 7
\]
Now, calculate it step-by-step:
1. Calculate \(-3 \times -5\):
\[
-3 \times -5 = 15
\]
2. Now subtract \(7\) from \(15\):
\[
15 - 7 = 8
\]
Therefore, the output is:
\[
\boxed{8}
\]