Watches

A watch is an expression that is re-evaluated on every stop and kept on screen. Ctrl+W opens the panel.

Use watches for the thing you are actually tracking — a counter, a flag, a field buried deep in a structure — instead of re-expanding the same path in Variables after every step.

Adding and removing

Key	Effect
Enter	enter the input field to type an expression
Esc	leave the input field
J / K	move between existing expressions
D / Del	remove the selected expression

Expressions are written in the debuggee's language, exactly as you would write them in the code at that point.

They are evaluated in the selected frame

A watch is evaluated in the stack frame currently selected in the Call Stack, not always the topmost one. Selecting a different frame re-evaluates every watch against it.

That means a watch can be valid in one frame and meaningless in another, which is expected: self exists in a method and not in main.

Results are trees too

A watch result is not necessarily a scalar. When the expression returns a structure or a collection, the row expands like any node in Variables — L / Right to open it — with the same lazy loading and the same pagination for large collections.

Watches and side effects

A watch expression runs in the debuggee. If it calls a function, that function executes — every time the program stops. An expression that mutates state, sends a request or writes a file will do so repeatedly, and will change the behaviour of the program you are debugging.

Keep watches to reads. For anything with a side effect, use Evaluate, where you control when it runs.

When a watch shows an error

The usual causes, in order of likelihood:

1. The expression is not valid in the selected frame — the variable is out of scope there.
2. The name is spelled differently than in the source, or is a macro or a compile-time construct the adapter cannot resolve.
3. The frame has no debug information, so nothing can be resolved in it.

An error in one watch does not affect the others.