SvelteKit on Cloudflare

Learn how to instrument your SvelteKit app on Cloudflare Workers and Pages and capture your first errors with Sentry.

You need:

A Sentry account and project
Your application up and running
SvelteKit version 2.0.0+ (we recommend 2.31.0 or higher for best support)
Vite version 4.2 or newer

I'm on an older SvelteKit version than 2.31.0

Version 2.31.0 of SvelteKit introduces official support for observability and tracing. This means that Sentry can now follow the official best practice for how the SDK should be set up. For you, this means:

The Sentry SDK will be initialized at the correct, earliest possible time on the server, allowing for all its auto-instrumentation to work correctly.
The Sentry SDK picks up spans emitted from SvelteKit directly. You'll get more accurate insights into the performance of your handlers, server actions, load, and remote functions.

SvelteKit observability is still an experimental feature in SvelteKit 2.x, but we recommend giving it a try. The Sentry wizard, as well as this guide, will use it as the default way of setting up the SDK.

Choose the features you want to configure, and this guide will show you how:

Want to learn more about these features?

Issues (always enabled): Sentry's core error monitoring product that automatically reports errors, uncaught exceptions, and unhandled rejections. If you have something that looks like an exception, Sentry can capture it.
Tracing: Track software performance while seeing the impact of errors across multiple systems. For example, distributed tracing allows you to follow a request from the frontend to the backend and back.
Session Replay: Get to the root cause of an issue faster by viewing a video-like reproduction of what was happening in the user's browser before, during, and after the problem.
Logs: Centralize and analyze your application logs to correlate them with errors and performance issues. Search, filter, and visualize log data to understand what's happening in your applications.

Run the command for your preferred package manager to add the Sentry SDK to your application:

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npm install @sentry/sveltekit --save

If you're updating your Sentry SDK to the latest version, check out our migration guide to learn more about breaking changes.

You need to initialize and configure the Sentry SDK in three places: the client side, the server side, and your Vite config.

Create a client hooks file src/hooks.client.(js|ts) in your project if you don't have one already. In this file, import and initialize the Sentry SDK and add the handleErrorWithSentry function to the handleError hook.

src/hooks.client.(js|ts)

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import * as Sentry from "@sentry/sveltekit";

Sentry.init({
  dsn: "https://examplePublicKey@o0.ingest.sentry.io/0example-org / example-project",

  // Adds request headers and IP for users, for more info visit:
  // https://docs.sentry.io/platforms/javascript/guides/sveltekit/configuration/options/#sendDefaultPii
  sendDefaultPii: true,
  //  performance

  // Set tracesSampleRate to 1.0 to capture 100%
  // of transactions for tracing.
  // We recommend adjusting this value in production
  // Learn more at
  // https://docs.sentry.io/platforms/javascript/configuration/options/#traces-sample-rate
  tracesSampleRate: 1.0,
  //  performance
  integrations: [
    //  session-replay
    Sentry.replayIntegration(),
    //  session-replay
    //  user-feedback
    Sentry.feedbackIntegration({
      // Additional SDK configuration goes in here, for example:
      colorScheme: "system",
    }),
    //  user-feedback
  ],

  //  session-replay
  // Capture Replay for 10% of all sessions,
  // plus for 100% of sessions with an error
  // Learn more at
  // https://docs.sentry.io/platforms/javascript/session-replay/configuration/#general-integration-configuration
  replaysSessionSampleRate: 0.1,
  replaysOnErrorSampleRate: 1.0,
  //  session-replay
  //  logs

  // Enable logs to be sent to Sentry
  enableLogs: true,
  //  logs
});

const myErrorHandler = ({ error, event }) => {
  console.error("An error occurred on the client side:", error, event);
};

export const handleError = Sentry.handleErrorWithSentry(myErrorHandler);

// or alternatively, if you don't have a custom error handler:
// export const handleError = handleErrorWithSentry();

Requires SvelteKit 2.31.0 or higher and @sentry/sveltekit 10.8.0 or higher.

Configure server-side instrumentation and tracing in your svelte.config.js file:

svelte.config.js

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const config = {
  kit: {
    experimental: {
      instrumentation: {
        server: true,
      },
      //  performance
      tracing: {
        server: true,
      },
      //  performance
    },
  },
};

export default config;

Create a server hooks file src/hooks.server.(js|ts) in your project if you don't have one already. In this file, import and initialize the Sentry SDK and add the handleErrorWithSentry function to the handleError hook and Sentry's Cloudflare request handler to the handle hook.

src/hooks.server.(js|ts)

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import {
  handleErrorWithSentry,
  sentryHandle,
  initCloudflareSentryHandle,
} from "@sentry/sveltekit";
import { sequence } from "@sveltejs/kit/hooks";
import * as Sentry from "@sentry/sveltekit";

export const handle = sequence(
  initCloudflareSentryHandle({
    dsn: "https://examplePublicKey@o0.ingest.sentry.io/0example-org / example-project",

    // Adds request headers and IP for users, for more info visit:
    // https://docs.sentry.io/platforms/javascript/guides/sveltekit/configuration/options/#sendDefaultPii
    sendDefaultPii: true,
    //  performance

    // Set tracesSampleRate to 1.0 to capture 100%
    // of transactions for tracing.
    // We recommend adjusting this value in production
    // Learn more at
    // https://docs.sentry.io/platforms/javascript/configuration/options/#traces-sample-rate
    tracesSampleRate: 1.0,
    //  performance
    //  logs

    // Enable logs to be sent to Sentry
    enableLogs: true,
    //  logs
  }),
  sentryHandle(),
);

const myErrorHandler = ({ error, event }) => {
  console.error("An error occurred on the server side:", error, event);
};

export const handleError = Sentry.handleErrorWithSentry(myErrorHandler);
// or alternatively, if you don't have a custom error handler:
// export const handleError = handleErrorWithSentry();

Add the sentrySvelteKit plugin before sveltekit in your vite.config.(js|ts) file to automatically upload source maps to Sentry and instrument load functions for tracing if it's configured.

vite.config.(js|ts)

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import { sveltekit } from "@sveltejs/kit/vite";
import { sentrySvelteKit } from "@sentry/sveltekit";
import { defineConfig } from "vite";

export default defineConfig({
  plugins: [sentrySvelteKit(), sveltekit()],
  // ... rest of your Vite config
});

Since the SDK needs access to the AsyncLocalStorage API, you need to set either the nodejs_compat or nodejs_als compatibility flags in your wrangler.(jsonc|toml) configuration file:

wrangler.jsonc

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{
  "compatibility_flags": [
    "nodejs_als",
    // "nodejs_compat"
  ],
}

Additionally, add the CF_VERSION_METADATA binding in the same file:

wrangler.jsonc

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{
  // ...
  "version_metadata": {
    "binding": "CF_VERSION_METADATA",
  },
}

To upload source maps for clear error stack traces, add your Sentry auth token, organization, and project slug in your vite.config.(js|ts) file:

vite.config.(js|ts)

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import { sveltekit } from "@sveltejs/kit/vite";
import { sentrySvelteKit } from "@sentry/sveltekit";

export default {
  plugins: [
    sentrySvelteKit({
      sourceMapsUploadOptions: {
        org: "example-org",
        project: "example-project",
        // store your auth token in an environment variable
        authToken: process.env.SENTRY_AUTH_TOKEN,
      },
    }),
    sveltekit(),
  ],
  // ... rest of your Vite config
};

To keep your auth token secure, always store it in an environment variable instead of directly in your files:

.env

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SENTRY_AUTH_TOKEN=sntrys_YOUR_TOKEN_HERE

Let's test your setup and confirm that Sentry is working correctly and sending data to your Sentry project.

To verify that Sentry captures errors and creates issues in your Sentry project, create a test page, for example, at src/routes/sentry-example/+page.svelte with a button that throws an error when clicked:

+page.svelte

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<script>
  function throwTestError() {
    throw new Error("Sentry Example Frontend Error");
  }
</script>

<button type="button" onclick="{throwTestError}">Throw error</button>

Important

Errors triggered from within your browser's developer tools (like the browser console) are sandboxed, so they will not trigger Sentry's error monitoring.

To test tracing, create a test API route like src/routes/sentry-example/+server.(js|ts):

+server.(js|ts)

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export const GET = async () => {
  throw new Error("Sentry Example API Route Error");
};

Next, update your test button to call this route and throw an error if the response isn't ok:

+page.svelte

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<script>
  import * as Sentry from "@sentry/sveltekit";

  function throwTestError() {
    Sentry.startSpan(
      {
        name: "Example Frontend Span",
        op: "test",
      },
      async () => {
        const res = await fetch("/sentry-example");
        if (!res.ok) {
          throw new Error("Sentry Example Frontend Error");
        }
      },
    );
  }
</script>

<button type="button" onclick="{throwTestError}">
  Throw error with trace
</button>

Open the page sentry-example in a browser and click the button to trigger two errors:

a frontend error
an error within the API route

Additionally, this starts a trace to measure the time it takes for the API request to complete.

Now, head over to your project on Sentry.io to view the collected data (it takes a couple of moments for the data to appear).

Need help locating the captured errors in your Sentry project?

Open the Issues page and select an error from the issues list to view the full details and context of this error. For more details, see this interactive walkthrough.
Open the Traces page and select a trace to reveal more information about each span, its duration, and any errors. For an interactive UI walkthrough, click here.
Open the Logs page and filter by service, environment, or search keywords to view log entries from your application. For an interactive UI walkthrough, click here.

At this point, you should have integrated Sentry into your SvelteKit application and should already be sending data to your Sentry project.

Now's a good time to customize your setup and look into more advanced topics. Our next recommended steps for you are:

Learn how to manually capture errors
Continue to customize your configuration
Get familiar with Sentry's product features like tracing, insights, and alerts
Learn how to manually instrument SvelteKit-specific features

Are you having problems setting up the SDK?

Find various support topics in Cloudflare troubleshooting and SvelteKit troubleshooting
Get support

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