feat(sveltekit): Add Compatibility for builtin SvelteKit Tracing #17423

Lms24 · 2025-08-14T17:02:30Z

This PR updates our SvelteKit SDK to be compatible with Sveltekit's new tracing feature, while maintaining backwards compatibility with Sentry<>SvelteKit setups on previous Kit versions or when SvelteKit's tracing feature is not used.

Nothing will change for users who use SvelteKit and Sentry without builtin SvelteKit tracing support.

If Kit tracing is used, the SDK

No longer starts its own http.server span but uses Kit's sveltekit.handle.root span as the http.server root span.
Configures our httpIntegration to avoid emitting a span for the incoming request span (this is in line with NextJS and Remix)
Processes kit-emitted spans to include sentry op and origin in an event preprocessing integration
Changes the name of root span to Sentry-esque http.server name conventions
- store original name as sveltekit.tracing.original_name attribute
Still isolates the request in addition

To detect at runtime, if Kit-native tracing is used, I had to make some build time adjustments

Read tracing config from svelte.config.js
Auto wrap universal load functions only for client-side code, if kit tracing is enabled
I also made a slight refactor of our globalValueInjection plugin which is now a standalone plugin, instead of mingled with the source maps upload plugin. Technically, this isn't necessary anymore after making more adjustments in this PR but I think it's still a good refactor, so I'd like to keep it.

Misc

Add tests for span processing
Add tests for build-time tracing config functionality
Add e2e test app with full tracing functionality enabled

Follow-up items to this PR

Better handling for remote functions. Right now, they don't produce nice traces because they're handled like non-route requests by sentryHandle. Decided to tackle this later since a) the feature is experimental and b) this PR is already too large. Sorry reviewers 😬
The Node adapter seems to hang when the SDK is used in instrumentation.server.ts and the server is shut down. We can fix this by listening to the process.on('sveltekit:shutdown') event.

see sveltejs/kit#13899

ref #16982

cc @elliott-with-the-longest-name-on-github

github-actions · 2025-08-26T16:31:54Z

size-limit report 📦

Path	Size	% Change	Change
@sentry/browser	24.16 kB	-	-
@sentry/browser - with treeshaking flags	22.73 kB	-	-
@sentry/browser (incl. Tracing)	39.87 kB	+0.01%	+1 B 🔺
@sentry/browser (incl. Tracing, Replay)	78.23 kB	-	-
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	68.02 kB	-	-
@sentry/browser (incl. Tracing, Replay with Canvas)	82.91 kB	+0.01%	+1 B 🔺
@sentry/browser (incl. Tracing, Replay, Feedback)	95.03 kB	-	-
@sentry/browser (incl. Feedback)	40.83 kB	-	-
@sentry/browser (incl. sendFeedback)	28.81 kB	-	-
@sentry/browser (incl. FeedbackAsync)	33.7 kB	-	-
@sentry/react	25.88 kB	-	-
@sentry/react (incl. Tracing)	41.87 kB	+0.01%	+1 B 🔺
@sentry/vue	28.64 kB	-	-
@sentry/vue (incl. Tracing)	41.69 kB	-	-
@sentry/svelte	24.18 kB	-	-
CDN Bundle	25.66 kB	+0.01%	+1 B 🔺
CDN Bundle (incl. Tracing)	39.75 kB	-	-
CDN Bundle (incl. Tracing, Replay)	76.03 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback)	81.46 kB	-	-
CDN Bundle - uncompressed	74.96 kB	-	-
CDN Bundle (incl. Tracing) - uncompressed	117.59 kB	-	-
CDN Bundle (incl. Tracing, Replay) - uncompressed	232.68 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	245.28 kB	-	-
@sentry/nextjs (client)	43.89 kB	-	-
@sentry/sveltekit (client)	40.32 kB	-	-
@sentry/node-core	47.99 kB	-	-
@sentry/node	149.25 kB	-	-
@sentry/node - without tracing	92.24 kB	+0.01%	+1 B 🔺
@sentry/aws-serverless	104.91 kB	-	-

View base workflow run

elliott-with-the-longest-name-on-github

just leaving a couple of comments!

elliott-with-the-longest-name-on-github · 2025-08-26T16:53:59Z

packages/sveltekit/src/server/sdk.ts

+  const defaultIntegrations = [...getDefaultNodeIntegrations(options), rewriteFramesIntegration()];
+
+  const config = getKitTracingConfig();
+  if (config.instrumentation) {
+    // Whenever `instrumentation` is enabled, we don't need httpIntegration to emit spans
+    // - if `tracing` is enabled, kit will emit the root span
+    // - if `tracing` is disabled, our handler will emit the root span
+    // In old (hooks.server.ts) based SDK setups, adding the default version of the integration does nothing
+    // for incoming requests. We still add it in default config for the undocumented case that anyone is
+    // using the SDK by `--import`ing the SDK setup directly (e.g. with adapter-node).
+    defaultIntegrations.push(httpIntegration({ disableIncomingRequestSpans: true }));
+    if (config.tracing) {
+      // If `tracing` is enabled, we need to instrument spans for the server
+      defaultIntegrations.push(svelteKitSpansIntegration());
+    }
+  }


So this works right now but I'm not sure if it will in SvelteKit 3 when we remove the experimental flag -- we plan on keeping a flag for tracing (you probably don't want SvelteKit emitting spans / including @opentelemetry/api in your bundle if you're not planning on using it), but the instrumentation flag is going to go away entirely -- users will either create an instrumentation file or not create one, and that signals to us whether or not we need to load it. It only has a flag right now so that people have to explicitly opt into the experimental nature (in case we need to make breaking changes).

That's good context, thanks Elliot!

but the instrumentation flag is going to go away entirely -- users will either create an instrumentation file or not create one

that makes sense of course. Didn't think of it but only expected the option to be lifted outside of experimental. In this case I think we can just be a bit more "naive" and avoid the conditional logic here. The only thing that will be problematic is the "undocumented" case of using the SDK with --import but not using Kit's tracing/instrumentation. Which I think we can ignore, given it's undocumented 😅

Which also means we likely don't need to inject the config at build time into the files at all 🎉 (we'll still need it at build time but for now I think that's fine).

elliott-with-the-longest-name-on-github · 2025-08-26T17:00:42Z

packages/sveltekit/src/vite/svelteConfig.ts

+ * Experimental tracing and instrumentation config is available
+ * @since 2.31.0
+ */
+type BackwardsForwardsCompatibleKitConfig = Config['kit'] & { experimental?: SvelteKitTracingConfig };


love the name 😆

chargome

Nice work! 🚀

chargome · 2025-08-27T11:59:50Z

packages/sveltekit/src/vite/sentryVitePlugins.ts

-  if (sentryVitePluginsOptions) {
-    const sentryVitePlugins = await makeCustomSentryVitePlugins(sentryVitePluginsOptions);
+  if (mergedOptions.autoUploadSourceMaps) {
+    sentryPlugins.push(await makeGlobalValuesInjectionPlugin(svelteConfig, mergedOptions));


Could use a comment: why is this plugin added when autoUploadSourceMaps is set

While writing this comment, I realized we should revisit if we even have to do this. All of this frames rewriting comes from pre-debugId times. For now I decided to leave it as-is, just to not change behaviour. But left a TODO to revisit this.

chargome · 2025-08-27T13:52:26Z

packages/sveltekit/src/server-common/integrations/svelteKitSpans.ts

+ */
+export function svelteKitSpansIntegration(): Integration {
+  return {
+    name: 'SvelteKitSpansEnhancment',


Suggested change

name: 'SvelteKitSpansEnhancment',

name: 'SvelteKitSpansEnhancement',

chargome · 2025-08-27T13:53:06Z

packages/sveltekit/src/server-common/integrations/svelteKitSpans.ts

+    // Using preprocessEvent to ensure the processing happens before user-configured
+    // event processors are executed
+    preprocessEvent(event) {
+      if (event.type === 'transaction') {


As discussed we could check if the root span comes from sveltekit here.

I realized this doesn't work on cloudflare because for some reason the sveltekit.handle.root span isn't emitted.
So our Cloudflare SDK emits the http.server span. Not sure why but I think this is something to follow up on. For now I wanna get a basic, working version out.

…n, change root span enhancement time

Lms24 changed the title ~~ref(sveltekit): Handle SvelteKit-generated spans in sentryHandle~~ feat(sveltekit): Add Compatibility for builtin SvelteKit Tracing Aug 25, 2025

Lms24 self-assigned this Aug 26, 2025

Lms24 force-pushed the lms/ref-sveltekit-tracing-handle-no-spans branch from c478f9d to bd930ce Compare August 26, 2025 16:29

Lms24 marked this pull request as ready for review August 26, 2025 16:29

Lms24 requested review from chargome and s1gr1d August 26, 2025 16:46

elliott-with-the-longest-name-on-github reviewed Aug 26, 2025

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chargome approved these changes Aug 27, 2025

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Lms24 added 16 commits August 27, 2025 20:17

ref(sveltekit): Handle SvelteKit-generated spans in sentryHandle

3993737

simplify

371fe0c

2.31.0

9c7f66d

process kit spans

bb028e1

wip but detect tracing config at SDK setup time

ea95125

comment

c389a1f

global values injection plugin, add tests, adjust existing tests

e728084

don't auto-wrap load functions if kit-tracing is enabled

72cc4a9

add e2e test app with kit-tracing enabled

529d718

fix span name, origin inconsistencies

b70134b

lint and remove remote function test

927cbf6

remove tracing config runtime check, cleanup, move some files

eebd5cc

lint

05091f5

fix failing unit test

cd9c441

improve tracing check, optimize svelteKitSpansIntegration

d265348

review suggestions, comments, revert kitSpansIntegrations optimizatio…

87c4109

…n, change root span enhancement time

Lms24 force-pushed the lms/ref-sveltekit-tracing-handle-no-spans branch from e27f7cc to 87c4109 Compare August 27, 2025 18:17

Lms24 merged commit e6e20d8 into develop Aug 27, 2025
162 checks passed

Lms24 deleted the lms/ref-sveltekit-tracing-handle-no-spans branch August 27, 2025 18:41

Lms24 mentioned this pull request Aug 27, 2025

Support new SvelteKit tracing feature #16982

Closed

Lms24 mentioned this pull request Aug 29, 2025

feat(sveltekit): Align build time options with shared type #17413

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