Introducing integrated observability in SvelteKit

SvelteKit apps can now emit OpenTelemetry traces and reliably set up observability instrumentation using instrumentation.server.ts

Elliott Johnson undefined 14 2025

Understanding how your SvelteKit application behaves in production -- from request flows to performance bottlenecks -- is crucial for building reliable user experiences. We’re excited to introduce two new experimental features that bring integrated observability directly into SvelteKit: built-in OpenTelemetry tracing and a dedicated instrumentation setup file that ensures your monitoring tools work seamlessly from day one.

First-party OpenTelemetry traces

SvelteKit can now emit OpenTelemetry traces for the following:

handle hook (handle functions running in a sequence will show up as children of each other and the root handle hook)
load functions (includes universal load functions when they’re run on the server)
Form actions
Remote functions

To enable trace emission, add the following to svelte.config.js:

svelte.config

export default {
	kit: {
    experimental: {
        tracing: {
 server: boolean;
        };
    };
}kit: {
		experimental: {
    tracing: {
        server: boolean;
    };
}experimental: {
			tracing: {
    server: boolean;
}tracing: {
				server: booleanserver: true
			}
		}           
	}
};

If there are additional attributes you think might be useful, please file an issue on the SvelteKit GitHub issue tracker.

A convenient home for all of your instrumentation

Emitting traces alone is not enough: You also need to collect them and send them somewhere. Under normal circumstances, this can be a bit challenging. Because of the nature of observability instrumentation, it needs to be loaded prior to loading any of the code from your app. To aid in this, SvelteKit now supports a src/instrumentation.server.ts file which, assuming your adapter supports it, is guaranteed to be loaded prior to your application code.

To enable instrumentation.server.ts, add the following to your svelte.config.js:

svelte.config

export default {
	kit: {
    experimental: {
        instrumentation: {
 server: boolean;
        };
    };
}kit: {
		experimental: {
    instrumentation: {
        server: boolean;
    };
}experimental: {
			instrumentation: {
    server: boolean;
}instrumentation: {
				server: booleanserver: true
			}
		}           
	}
};

In Node, your instrumentation might look something like this:

import { import NodeSDKNodeSDK } from '@opentelemetry/sdk-node';
import { import getNodeAutoInstrumentationsgetNodeAutoInstrumentations } from '@opentelemetry/auto-instrumentations-node';
import { import OTLPTraceExporterOTLPTraceExporter } from '@opentelemetry/exporter-trace-otlp-proto';
import { import createAddHookMessageChannelcreateAddHookMessageChannel } from 'import-in-the-middle';
import { function register<Data = any>(specifier: string | URL, parentURL?: string | URL, options?: Module.RegisterOptions<Data>): void (+1 overload)Register a module that exports hooks that customize Node.js module
resolution and loading behavior. See
Customization hooks.
@sincev20.6.0, v18.19.0
@paramspecifier Customization hooks to be registered; this should be
the same string that would be passed to import(), except that if it is
relative, it is resolved relative to parentURL.
@paramparentURL f you want to resolve specifier relative to a base
URL, such as import.meta.url, you can pass that URL here.register } from 'module';

const { const registerOptions: anyregisterOptions } = import createAddHookMessageChannelcreateAddHookMessageChannel();
register<any>(specifier: string | URL, parentURL?: string | URL, options?: Module.RegisterOptions<any> | undefined): void (+1 overload)Register a module that exports hooks that customize Node.js module
resolution and loading behavior. See
Customization hooks.
@sincev20.6.0, v18.19.0
@paramspecifier Customization hooks to be registered; this should be
the same string that would be passed to import(), except that if it is
relative, it is resolved relative to parentURL.
@paramparentURL f you want to resolve specifier relative to a base
URL, such as import.meta.url, you can pass that URL here.register('import-in-the-middle/hook.mjs', import.meta.ImportMeta.url: stringThe absolute file: URL of the module.
url, const registerOptions: anyregisterOptions);

const const sdk: anysdk = new import NodeSDKNodeSDK({
	serviceName: stringserviceName: 'test-sveltekit-tracing',
	traceExporter: anytraceExporter: new import OTLPTraceExporterOTLPTraceExporter(),
	instrumentations: any[]instrumentations: [import getNodeAutoInstrumentationsgetNodeAutoInstrumentations()]
});

const sdk: anysdk.start();

...and on Vercel, it would look something like this:

import { import registerOTelregisterOTel } from '@vercel/otel';

import registerOTelregisterOTel({
	serviceName: stringserviceName: 'test-sveltekit-tracing'
});

Consult your platform’s documentation for specific instrumentation instructions. As of now, all of the official SvelteKit adapters with a server component (sorry, adapter-static) support instrumentation.server.ts.

Acknowledgements

A huge thank-you to Lukas Stracke, who kicked us off on this adventure with his excellent talk at Svelte Summit 2025 and his initial draft PR for instrumentation.server.ts. Another thank-you to Sentry for allowing him to spend his working hours reviewing and testing our work.