svelte/documentation/docs/03-template-syntax/11-@debug.md

title: {@debug ...}

The {@debug ...} tag offers an alternative to console.log(...). It logs the values of specific variables whenever they change, and pauses code execution if you have devtools open.

<script>
	let user = {
		firstname: 'Ada',
		lastname: 'Lovelace'
	};
</script>

{@debug user}

<h1>Hello {user.firstname}!</h1>

{@debug ...} accepts a comma-separated list of variable names (not arbitrary expressions).

<!-- Compiles -->
{@debug user}
{@debug user1, user2, user3}

<!-- WON'T compile -->
{@debug user.firstname}
{@debug myArray[0]}
{@debug !isReady}
{@debug typeof user === 'object'}

The {@debug} tag without any arguments will insert a debugger statement that gets triggered when any state changes, as opposed to the specified variables.

{@debug ...} vs $inspect

{@debug} and $inspect both exist because one is a template debugger and the other is a <script> rune. {@debug} is not deprecated.

Reach for {@debug} when the value you care about is used in markup and you want DevTools to pause (debugger) when it changes. It only accepts identifiers, not expressions.

Reach for $inspect when you are already in <script>, need to log an expression, or want deep reactive tracking that is stripped from production builds. If you only need a breakpoint from script, $inspect(value).with(() => { debugger; }) is the rune equivalent of {@debug}.