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The main @sveltejs/kit module exports core utilities for building SvelteKit applications, including error handling, redirects, and response helpers.

​
error

Throws an error with an HTTP status code and optional message. When called during request handling, this will cause SvelteKit to return an error response without invoking handleError.
Make sure you’re not catching the thrown error, which would prevent SvelteKit from handling it.
​
status
number
required
The HTTP status code. Must be in the range 400-599.
​
body
App.Error | string
An object that conforms to the App.Error type. If a string is passed, it will be used as the message property.
​
return
never
This function never returns - it always throws.
import { error } from '@sveltejs/kit';

// In a server load function
export function load({ params }) {
  const post = db.getPost(params.id);
  
  if (!post) {
    error(404, 'Post not found');
  }
  
  return { post };
}

// With custom error object
error(400, {
  message: 'Invalid request',
  code: 'VALIDATION_ERROR'
});

​
isHttpError

Checks whether an error was thrown by the error function.
​
e
unknown
required
The error object to check.
​
status
number
Optional status code to filter for. If provided, the function will only return true if the error matches this specific status.
​
return
boolean
Returns true if the error is an HttpError (and optionally matches the status), false otherwise.
import { error, isHttpError } from '@sveltejs/kit';

try {
  // some code
} catch (e) {
  if (isHttpError(e) && e.status === 404) {
    // Handle 404 specifically
  }
}

​
redirect

Redirect a request. When called during request handling, SvelteKit will return a redirect response.
Make sure you’re not catching the thrown redirect, which would prevent SvelteKit from handling it.
Most common status codes:
  • 303 See Other: redirect as a GET request (often used after a form POST request)
  • 307 Temporary Redirect: redirect will keep the request method
  • 308 Permanent Redirect: redirect will keep the request method, SEO will be transferred to the new page
See all redirect status codes
​
status
300 | 301 | 302 | 303 | 304 | 305 | 306 | 307 | 308
required
The HTTP status code. Must be in the range 300-308.
​
location
string | URL
required
The location to redirect to.
​
return
never
This function never returns - it always throws a Redirect.
import { redirect } from '@sveltejs/kit';

export function load() {
  redirect(307, '/login');
}

// After form submission
export const actions = {
  default: async ({ request }) => {
    // process form...
    redirect(303, '/success');
  }
};

​
isRedirect

Checks whether an error is a redirect thrown by the redirect function.
​
e
unknown
required
The object to check.
​
return
boolean
Returns true if the error is a Redirect, false otherwise.
import { isRedirect } from '@sveltejs/kit';

try {
  // some code that might redirect
} catch (e) {
  if (isRedirect(e)) {
    // Handle redirect
  }
}

​
json

Create a JSON Response object from the supplied data.
​
data
any
required
The value that will be serialized as JSON.
​
init
ResponseInit
Options such as status and headers that will be added to the response. Content-Type: application/json and Content-Length headers will be added automatically.
​
return
Response
A Response object with JSON content.
import { json } from '@sveltejs/kit';

export function GET() {
  return json({
    message: 'Hello world',
    timestamp: Date.now()
  });
}

// With custom status and headers
export function POST() {
  return json(
    { success: true },
    { 
      status: 201,
      headers: {
        'cache-control': 'max-age=60'
      }
    }
  );
}

​
text

Create a Response object from the supplied body.
​
body
string
required
The value that will be used as-is.
​
init
ResponseInit
Options such as status and headers that will be added to the response. A Content-Length header will be added automatically.
​
return
Response
A Response object with text content.
import { text } from '@sveltejs/kit';

export function GET() {
  return text('Hello world');
}

// With custom headers
export function GET() {
  return text(
    'Hello world',
    {
      headers: {
        'content-type': 'text/plain; charset=utf-8'
      }
    }
  );
}

​
fail

Create an ActionFailure object. Use this to return data and an appropriate status code when form submission fails.
​
status
number
required
The HTTP status code. Must be in the range 400-599.
​
data
T
Data associated with the failure (e.g. validation errors).
​
return
ActionFailure<T>
An ActionFailure object containing the status and data.
import { fail } from '@sveltejs/kit';

export const actions = {
  default: async ({ request }) => {
    const data = await request.formData();
    const email = data.get('email');
    
    if (!email) {
      return fail(400, { 
        error: 'Email is required',
        email 
      });
    }
    
    // process form...
  }
};

​
isActionFailure

Checks whether an object is an action failure returned by the fail function.
​
e
unknown
required
The object to check.
​
return
boolean
Returns true if the object is an ActionFailure, false otherwise.
import { isActionFailure } from '@sveltejs/kit';

const result = await fetch('/api/endpoint');
if (isActionFailure(result)) {
  console.log('Action failed with status:', result.status);
}

​
invalid

Throw a validation error to imperatively fail form validation. Can be used in combination with issue passed to form actions to create field-specific issues.
Available since version 2.47.3
​
issues
StandardSchemaV1.Issue | string
required
One or more validation issues. Can be issue objects or simple error message strings.
​
return
never
This function never returns - it always throws a ValidationError.
import { invalid } from '@sveltejs/kit';
import { form } from '$app/server';
import { tryLogin } from '$lib/server/auth';
import * as v from 'valibot';

export const login = form(
  v.object({ name: v.string(), _password: v.string() }),
  async ({ name, _password }) => {
    const success = tryLogin(name, _password);
    if (!success) {
      invalid('Incorrect username or password');
    }
    
    // ...
  }
);

​
isValidationError

Checks whether an error is a validation error thrown by the invalid function.
Available since version 2.47.3
​
e
unknown
required
The object to check.
​
return
boolean
Returns true if the error is a ValidationError, false otherwise.
import { isValidationError } from '@sveltejs/kit';

try {
  // validation code
} catch (e) {
  if (isValidationError(e)) {
    console.log('Validation failed:', e.issues);
  }
}

​
normalizeUrl

Strips possible SvelteKit-internal suffixes and trailing slashes from the URL pathname. Returns the normalized URL as well as a method for adding the potential suffix back based on a new pathname (possibly including search) or URL.
Available since version 2.18.0
​
url
URL | string
required
The URL to normalize.
​
url
URL
The normalized URL object.
​
wasNormalized
boolean
Whether the URL was actually normalized (had suffixes or trailing slash).
​
denormalize
(url?: string | URL) => URL
A function to add the suffix back to a new URL.
import { normalizeUrl } from '@sveltejs/kit';

const { url, denormalize } = normalizeUrl('/blog/post/__data.json');
console.log(url.pathname); // /blog/post
console.log(denormalize('/blog/post/a')); // /blog/post/a/__data.json

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VERSION

The current version of SvelteKit. 
import { VERSION } from '@sveltejs/kit';

console.log('SvelteKit version:', VERSION);