Ky is a tiny and elegant HTTP client based on the Fetch API

Ky targets modern browsers, Node.js, Bun, and Deno.

It's just a tiny package with no dependencies.

Benefits over plain `fetch`

Simpler API
Method shortcuts (ky.post())
Treats non-2xx status codes as errors (after redirects)
Retries failed requests
JSON option
Timeout support
URL prefix option
Instances with custom defaults
Hooks
TypeScript niceties (e.g. .json() supports generics and defaults to unknown, not any)

Install

npm install ky

CDN

Usage

import ky from 'ky';

const json = await ky.post('https://example.com', {json: {foo: true}}).json();

console.log(json);
//=> {data: '🦄'}

With plain fetch, it would be:

class HTTPError extends Error {}

const response = await fetch('https://example.com', {
	method: 'POST',
	body: JSON.stringify({foo: true}),
	headers: {
		'content-type': 'application/json'
	}
});

if (!response.ok) {
	throw new HTTPError(`Fetch error: ${response.statusText}`);
}

const json = await response.json();

console.log(json);
//=> {data: '🦄'}

If you are using Deno, import Ky from a URL. For example, using a CDN:

import ky from 'https://esm.sh/ky';

API

ky(input, options?)

The input and options are the same as fetch, with additional options available (see below).

Returns a Response object with Body methods added for convenience. So you can, for example, call ky.get(input).json() directly without having to await the Response first. When called like that, an appropriate Accept header will be set depending on the body method used. Unlike the Body methods of window.Fetch, these will throw an HTTPError if the response status is not in the range of 200...299. Also, .json() will return an empty string if body is empty or the response status is 204 instead of throwing a parse error due to an empty body.

Available body shortcuts: .json(), .text(), .formData(), .arrayBuffer(), .blob(), and .bytes(). The .bytes() shortcut is only present when the runtime supports Response.prototype.bytes().

import ky from 'ky';

const user = await ky('/api/user').json();

console.log(user);

⌨️ TypeScript: Accepts an optional type parameter, which defaults to unknown, and is passed through to the return type of .json().

import ky from 'ky';

// user1 is unknown
const user1 = await ky('/api/users/1').json();
// user2 is a User
const user2 = await ky<User>('/api/users/2').json();
// user3 is a User
const user3 = await ky('/api/users/3').json<User>();

console.log([user1, user2, user3]);

// Get raw bytes (when supported by the runtime)
const bytes = await ky('/api/file').bytes();
console.log(bytes instanceof Uint8Array);

ky.get(input, options?)

ky.post(input, options?)

ky.put(input, options?)

ky.patch(input, options?)

ky.head(input, options?)

ky.delete(input, options?)

Sets options.method to the method name and makes a request.

⌨️ TypeScript: Accepts an optional type parameter for use with JSON responses (see ky()).

input

Type: string | URL | Request

Same as fetch input.

When using a Request instance as input, any URL altering options (such as prefixUrl) will be ignored.

options

Type: object

Same as fetch options, plus the following additional options:

method

Type: string
Default: 'get'

HTTP method used to make the request.

Internally, the standard methods (GET, POST, PUT, PATCH, HEAD and DELETE) are uppercased in order to avoid server errors due to case sensitivity.

json

Type: object and any other value accepted by JSON.stringify()

Shortcut for sending JSON. Use this instead of the body option. Accepts any plain object or value, which will be JSON.stringify()'d and sent in the body with the correct header set.

searchParams

Search parameters to include in the request URL. Setting this will override all existing search parameters in the input URL.

Accepts any value supported by URLSearchParams().

When passing an object, undefined values are automatically filtered out, while null values are preserved and converted to the string 'null'.

prefixUrl

Type: string | URL

A prefix to prepend to the input URL when making the request. It can be any valid URL, either relative or absolute. A trailing slash / is optional and will be added automatically, if needed, when it is joined with input. Only takes effect when input is a string. The input argument cannot start with a slash / when using this option.

Useful when used with ky.extend() to create niche-specific Ky-instances.

import ky from 'ky';

// On https://example.com

const response = await ky('unicorn', {prefixUrl: '/api'});
//=> 'https://example.com/api/unicorn'

const response2 = await ky('unicorn', {prefixUrl: 'https://cats.com'});
//=> 'https://cats.com/unicorn'

Notes:

After prefixUrl and input are joined, the result is resolved against the base URL of the page (if any).
Leading slashes in input are disallowed when using this option to enforce consistency and avoid confusion about how the input URL is handled, given that input will not follow the normal URL resolution rules when prefixUrl is being used, which changes the meaning of a leading slash.

retry

Type: object | number
Default:

limit: 2
methods: get put head delete options trace
statusCodes: 408 413 429 500 502 503 504
afterStatusCodes: 413, 429, 503
maxRetryAfter: undefined
backoffLimit: undefined
delay: attemptCount => 0.3 * (2 ** (attemptCount - 1)) * 1000
jitter: undefined
retryOnTimeout: false
shouldRetry: undefined

An object representing limit, methods, statusCodes, afterStatusCodes, maxRetryAfter, backoffLimit, delay, jitter, retryOnTimeout, and shouldRetry fields for maximum retry count, allowed methods, allowed status codes, status codes allowed to use the Retry-After time, maximum Retry-After time, backoff limit, delay calculation function, retry jitter, timeout retry behavior, and custom retry logic.

If retry is a number, it will be used as limit and other defaults will remain in place.

If the response provides an HTTP status contained in afterStatusCodes, Ky will wait until the date, timeout, or timestamp given in the Retry-After header has passed to retry the request. If Retry-After is missing, the non-standard RateLimit-Reset header is used in its place as a fallback. If the provided status code is not in the list, the Retry-After header will be ignored.

If maxRetryAfter is set to undefined, it will use options.timeout. If Retry-After header is greater than maxRetryAfter, it will use maxRetryAfter.

The backoffLimit option is the upper limit of the delay per retry in milliseconds. To clamp the delay, set backoffLimit to 1000, for example. By default, the delay is calculated with 0.3 * (2 ** (attemptCount - 1)) * 1000. The delay increases exponentially.

The delay option can be used to change how the delay between retries is calculated. The function receives one parameter, the attempt count, starting at 1.

The jitter option adds random jitter to retry delays to prevent thundering herd problems. When many clients retry simultaneously (e.g., after hitting a rate limit), they can overwhelm the server again. Jitter adds randomness to break this synchronization. Set to true to use full jitter, which randomizes the delay between 0 and the computed delay. Alternatively, pass a function to implement custom jitter strategies.

Note: Jitter is not applied when the server provides a Retry-After header, as the server's explicit timing should be respected.

The retryOnTimeout option determines whether to retry when a request times out. By default, retries are not triggered following a timeout.

The shouldRetry option provides custom retry logic that takes precedence over all other retry checks. This function is called first, before any other retry validation.

Note: This is different from the beforeRetry hook:

shouldRetry: Controls WHETHER to retry (called before the retry decision is made)
beforeRetry: Called AFTER retry is confirmed, allowing you to modify the request

The function receives a state object with the error and retry count (starts at 1 for the first retry), and should return:

true to force a retry (bypasses retryOnTimeout, status code checks, and other validations)
false to prevent a retry (no retry will occur)
undefined to use the default retry logic (retryOnTimeout, status codes, etc.)

General example

import ky from 'ky';

const json = await ky('https://example.com', {
	retry: {
		limit: 10,
		methods: ['get'],
		statusCodes: [413],
		backoffLimit: 3000
	}
}).json();

Retrying on timeout:

import ky from 'ky';

const json = await ky('https://example.com', {
	timeout: 5000,
	retry: {
		limit: 3,
		retryOnTimeout: true
	}
}).json();

Using jitter to prevent thundering herd:

import ky from 'ky';

const json = await ky('https://example.com', {
	retry: {
		limit: 5,

		// Full jitter (randomizes delay between 0 and computed value)
		jitter: true

		// Percentage jitter (80-120% of delay)
		// jitter: delay => delay * (0.8 + Math.random() * 0.4)

		// Absolute jitter (±100ms)
		// jitter: delay => delay + (Math.random() * 200 - 100)
	}
}).json();

Custom retry logic:

import ky, {HTTPError} from 'ky';

const json = await ky('https://example.com', {
	retry: {
		limit: 3,
		shouldRetry: ({error, retryCount}) => {
			// Retry on specific business logic errors from API
			if (error instanceof HTTPError) {
				const status = error.response.status;

				// Retry on 429 (rate limit) but only for first 2 attempts
				if (status === 429 && retryCount <= 2) {
					return true;
				}

				// Don't retry on 4xx errors except rate limits
				if (status >= 400 && status < 500) {
					return false;
				}
			}

			// Use default retry logic for other errors
			return undefined;
		}
	}
}).json();

Note

Chromium-based browsers automatically retry 408 Request Timeout responses at the network layer for keep-alive connections. This means requests may be retried by both the browser and ky. If you want to avoid duplicate retries, you can either set keepalive: false in your request options (though this may impact performance for multiple requests) or remove 408 from the retry status codes.

timeout

Type: number | false
Default: 10000

Timeout in milliseconds for getting a response, including any retries. Can not be greater than 2147483647. If set to false, there will be no timeout.

hooks

Type: object<string, Function[]>
Default: {beforeRequest: [], beforeRetry: [], afterResponse: []}

Hooks allow modifications during the request lifecycle. Hook functions may be async and are run serially.

hooks.beforeRequest

Type: Function[]
Default: []

This hook enables you to modify the request right before it is sent. Ky will make no further changes to the request after this. The hook function receives the normalized request, options, and a state object. You could, for example, modify the request.headers here.

The state.retryCount is 0 for the initial request and increments with each retry. This allows you to distinguish between initial requests and retries, which is useful when you need different behavior for retries (e.g., avoiding overwriting headers set in beforeRetry).

The hook can return a Request to replace the outgoing request, or return a Response to completely avoid making an HTTP request. This can be used to mock a request, check an internal cache, etc. An important consideration when returning a request or response from this hook is that any remaining beforeRequest hooks will be skipped, so you may want to only return them from the last hook.

import ky from 'ky';

const api = ky.extend({
	hooks: {
		beforeRequest: [
			(request, options, {retryCount}) => {
				// Only set default auth header on initial request, not on retries
				// (retries may have refreshed token set by beforeRetry)
				if (retryCount === 0) {
					request.headers.set('Authorization', 'token initial-token');
				}
			}
		]
	}
});

const response = await api.get('https://example.com/api/users');

hooks.beforeRetry

Type: Function[]
Default: []

This hook enables you to modify the request right before retry. Ky will make no further changes to the request after this. The hook function receives an object with the normalized request and options, an error instance, and the retry count. You could, for example, modify request.headers here.

The hook can return a Request to replace the outgoing retry request, or return a Response to skip the retry and use that response instead. Note: Returning a request or response skips remaining beforeRetry hooks.

The retryCount is always >= 1 since this hook is only called during retries, not on the initial request.

If the request received a response, the error will be of type HTTPError and the Response object will be available at error.response. Be aware that some types of errors, such as network errors, inherently mean that a response was not received. In that case, the error will not be an instance of HTTPError.

You can prevent Ky from retrying the request by throwing an error. Ky will not handle it in any way and the error will be propagated to the request initiator. The rest of the beforeRetry hooks will not be called in this case. Alternatively, you can return the ky.stop symbol to do the same thing but without propagating an error (this has some limitations, see ky.stop docs for details).

Modifying headers:

import ky from 'ky';

const response = await ky('https://example.com', {
	hooks: {
		beforeRetry: [
			async ({request, options, error, retryCount}) => {
				const token = await ky('https://example.com/refresh-token');
				request.headers.set('Authorization', `token ${token}`);
			}
		]
	}
});

Modifying the request URL:

import ky from 'ky';

const response = await ky('https://example.com/api', {
	hooks: {
		beforeRetry: [
			async ({request, error}) => {
				// Add query parameters based on error response
				if (error.response) {
					const body = await error.response.json();
					const url = new URL(request.url);
					url.searchParams.set('processId', body.processId);
					return new Request(url, request);
				}
			}
		]
	}
});

Returning a cached response:

import ky from 'ky';

const response = await ky('https://example.com/api', {
	hooks: {
		beforeRetry: [
			({error, retryCount}) => {
				// Use cached response instead of retrying
				if (retryCount > 1 && cachedResponse) {
					return cachedResponse;
				}
			}
		]
	}
});

hooks.beforeError

Type: Function[]
Default: []

This hook enables you to modify the HTTPError right before it is thrown. The hook function receives a HTTPError and a state object as arguments and should return an instance of HTTPError.

The state.retryCount is 0 for the initial request and increments with each retry. This allows you to distinguish between the initial request and retries, which is useful when you need different error handling based on retry attempts (e.g., showing different error messages on the final attempt).

import ky from 'ky';

await ky('https://example.com', {
	hooks: {
		beforeError: [
			async error => {
				const {response} = error;
				if (response) {
					const body = await response.json();
					error.name = 'GitHubError';
					error.message = `${body.message} (${response.status})`;
				}

				return error;
			},

			// Or show different message based on retry count
			(error, state) => {
				if (state.retryCount === error.options.retry.limit) {
					error.message = `${error.message} (failed after ${state.retryCount} retries)`;
				}

				return error;
			}
		]
	}
});

hooks.afterResponse

Type: Function[]
Default: []

This hook enables you to read and optionally modify the response. The hook function receives normalized request, options, a clone of the response, and a state object. The return value of the hook function will be used by Ky as the response object if it's an instance of Response.

You can also force a retry by returning ky.retry(options). This is useful when you need to retry based on the response body content, even if the response has a successful status code. The retry will respect the retry.limit option and be observable in beforeRetry hooks.

The state.retryCount is 0 for the initial request and increments with each retry. This allows you to distinguish between initial requests and retries, which is useful when you need different behavior for retries (e.g., showing a notification only on the final retry).

import ky from 'ky';

const response = await ky('https://example.com', {
	hooks: {
		afterResponse: [
			(_request, _options, response) => {
				// You could do something with the response, for example, logging.
				log(response);

				// Or return a `Response` instance to overwrite the response.
				return new Response('A different response', {status: 200});
			},

			// Or retry with a fresh token on a 403 error
			async (request, options, response) => {
				if (response.status === 403) {
					// Get a fresh token
					const token = await ky('https://example.com/token').text();

					// Retry with the token
					request.headers.set('Authorization', `token ${token}`);

					return ky(request, options);
				}
			},

			// Or force retry based on response body content
			async (request, options, response) => {
				if (response.status === 200) {
					const data = await response.clone().json();
					if (data.error?.code === 'RATE_LIMIT') {
						// Retry with custom delay from API response
						return ky.retry({
							delay: data.error.retryAfter * 1000,
							code: 'RATE_LIMIT'
						});
					}
				}
			},

			// Or show a notification only on the last retry for 5xx errors
			(request, options, response, {retryCount}) => {
				if (response.status >= 500 && response.status <= 599) {
					if (retryCount === options.retry.limit) {
						showNotification('Request failed after all retries');
					}
				}
			}
		]
	}
});

throwHttpErrors

Type: boolean | (status: number) => boolean
Default: true

Throw an HTTPError when, after following redirects, the response has a non-2xx status code. To also throw for redirects instead of following them, set the redirect option to 'manual'.

Setting this to false may be useful if you are checking for resource availability and are expecting error responses.

You can also pass a function that accepts the HTTP status code and returns a boolean for selective error handling. Note that this can violate the principle of least surprise, so it's recommended to use the boolean form unless you have a specific use case like treating 404 responses differently.

Note: If false, error responses are considered successful and the request will not be retried.

onDownloadProgress

Type: Function

Download progress event handler.

The function receives these arguments:

progress is an object with the these properties:
- percent is a number between 0 and 1 representing the progress percentage.
- transferredBytes is the number of bytes transferred so far.
- totalBytes is the total number of bytes to be transferred. This is an estimate and may be 0 if the total size cannot be determined.
chunk is an instance of Uint8Array containing the data that was sent. Note: It's empty for the first call.

import ky from 'ky';

const response = await ky('https://example.com', {
	onDownloadProgress: (progress, chunk) => {
		// Example output:
		// `0% - 0 of 1271 bytes`
		// `100% - 1271 of 1271 bytes`
		console.log(`${progress.percent * 100}% - ${progress.transferredBytes} of ${progress.totalBytes} bytes`);
	}
});

onUploadProgress

Type: Function

Upload progress event handler.

The function receives these arguments:

progress is an object with the these properties:
- percent is a number between 0 and 1 representing the progress percentage.
- transferredBytes is the number of bytes transferred so far.
- totalBytes is the total number of bytes to be transferred. This is an estimate and may be 0 if the total size cannot be determined.
chunk is an instance of Uint8Array containing the data that was sent. Note: It's empty for the last call.

import ky from 'ky';

const response = await ky.post('https://example.com/upload', {
	body: largeFile,
	onUploadProgress: (progress, chunk) => {
		// Example output:
		// `0% - 0 of 1271 bytes`
		// `100% - 1271 of 1271 bytes`
		console.log(`${progress.percent * 100}% - ${progress.transferredBytes} of ${progress.totalBytes} bytes`);
	}
});

parseJson

Type: Function
Default: JSON.parse()

User-defined JSON-parsing function.

Use-cases:

Parse JSON via the bourne package to protect from prototype pollution.
Parse JSON with reviver option of JSON.parse().

import ky from 'ky';
import bourne from '@hapijs/bourne';

const json = await ky('https://example.com', {
	parseJson: text => bourne(text)
}).json();

stringifyJson

Type: Function
Default: JSON.stringify()

User-defined JSON-stringifying function.

Use-cases:

Stringify JSON with a custom replacer function.

import ky from 'ky';
import {DateTime} from 'luxon';

const json = await ky('https://example.com', {
	stringifyJson: data => JSON.stringify(data, (key, value) => {
		if (key.endsWith('_at')) {
			return DateTime.fromISO(value).toSeconds();
		}

		return value;
	})
}).json();

fetch

Type: Function
Default: fetch

User-defined fetch function. Has to be fully compatible with the Fetch API standard.

Use-cases:

Use custom fetch implementations like isomorphic-unfetch.
Use the fetch wrapper function provided by some frameworks that use server-side rendering (SSR).

import ky from 'ky';
import fetch from 'isomorphic-unfetch';

const json = await ky('https://example.com', {fetch}).json();

context

Type: object<string, unknown>
Default: {}

User-defined data passed to hooks.

This option allows you to pass arbitrary contextual data to hooks without polluting the request itself. The context is available in all hooks and is guaranteed to always be an object (never undefined), so you can safely access properties without optional chaining.

Use cases:

Pass authentication tokens or API keys to hooks
Attach request metadata for logging or debugging
Implement conditional logic in hooks based on the request context
Pass serverless environment bindings (e.g., Cloudflare Workers)

Note: Context is shallow merged. Top-level properties are merged, but nested objects are replaced. Only enumerable properties are copied.

import ky from 'ky';

// Pass data to hooks
const api = ky.create({
	hooks: {
		beforeRequest: [
			(request, options) => {
				const {token} = options.context;
				if (token) {
					request.headers.set('Authorization', `Bearer ${token}`);
				}
			}
		]
	}
});

await api('https://example.com', {
	context: {
		token: 'secret123'
	}
}).json();

// Shallow merge: only top-level properties are merged
const instance = ky.create({
	context: {
		a: 1,
		b: {
			nested: true
		}
	}
});

const extended = instance.extend({
	context: {
		b: {
			updated: true
		},
		c: 3
	}
});
// Result: {a: 1, b: {updated: true}, c: 3}
// Note: The original `b.nested` is gone (shallow merge)

ky.extend(defaultOptions)

Create a new ky instance with some defaults overridden with your own.

In contrast to ky.create(), ky.extend() inherits defaults from its parent.

You can pass headers as a Headers instance or a plain object.

You can remove a header with .extend() by passing the header with an undefined value. Passing undefined as a string removes the header only if it comes from a Headers instance.

Similarly, you can remove existing hooks entries by extending the hook with an explicit undefined.

import ky from 'ky';

const url = 'https://sindresorhus.com';

const original = ky.create({
	headers: {
		rainbow: 'rainbow',
		unicorn: 'unicorn'
	},
	hooks: {
		beforeRequest: [ () => console.log('before 1') ],
		afterResponse: [ () => console.log('after 1') ],
	},
});

const extended = original.extend({
	headers: {
		rainbow: undefined
	},
	hooks: {
		beforeRequest: undefined,
		afterResponse: [ () => console.log('after 2') ],
	}
});

const response = await extended(url).json();
//=> after 1
//=> after 2

console.log('rainbow' in response);
//=> false

console.log('unicorn' in response);
//=> true

You can also refer to parent defaults by providing a function to .extend().

import ky from 'ky';

const api = ky.create({prefixUrl: 'https://example.com/api'});

const usersApi = api.extend((options) => ({prefixUrl: `${options.prefixUrl}/users`}));

const response = await usersApi.get('123');
//=> 'https://example.com/api/users/123'

const response = await api.get('version');
//=> 'https://example.com/api/version'

ky.create(defaultOptions)

Create a new Ky instance with complete new defaults.

import ky from 'ky';

// On https://my-site.com

const api = ky.create({prefixUrl: 'https://example.com/api'});

const response = await api.get('users/123');
//=> 'https://example.com/api/users/123'

const response = await api.get('/status', {prefixUrl: ''});
//=> 'https://my-site.com/status'

defaultOptions

Type: object

ky.stop

A Symbol that can be returned by a beforeRetry hook to stop the retry. This will also short circuit the remaining beforeRetry hooks.

Note: Returning this symbol makes Ky abort and return with an undefined response. Be sure to check for a response before accessing any properties on it or use optional chaining. It is also incompatible with body methods, such as .json() or .text(), because there is no response to parse. In general, we recommend throwing an error instead of returning this symbol, as that will cause Ky to abort and then throw, which avoids these limitations.

A valid use-case for ky.stop is to prevent retries when making requests for side effects, where the returned data is not important. For example, logging client activity to the server.

import ky from 'ky';

const options = {
	hooks: {
		beforeRetry: [
			async ({request, options, error, retryCount}) => {
				const shouldStopRetry = await ky('https://example.com/api');
				if (shouldStopRetry) {
					return ky.stop;
				}
			}
		]
	}
};

// Note that response will be `undefined` in case `ky.stop` is returned.
const response = await ky.post('https://example.com', options);

// Using `.text()` or other body methods is not supported.
const text = await ky('https://example.com', options).text();

ky.retry(options?)

Force a retry from an afterResponse hook.

This allows you to retry a request based on the response content, even if the response has a successful status code. The retry will respect the retry.limit option and skip the shouldRetry check. The forced retry is observable in beforeRetry hooks, where the error will be a ForceRetryError with the error name 'ForceRetryError'.

options

Type: object

delay

Type: number

Custom delay in milliseconds before retrying. If not provided, uses the default retry delay calculation based on retry.delay configuration.

Note: Custom delays bypass jitter and backoffLimit. This is intentional, as custom delays often come from server responses (e.g., Retry-After headers) and should be respected exactly as specified.

code

Type: string

Error code for the retry.

This machine-readable identifier will be included in the error message passed to beforeRetry hooks, allowing you to distinguish between different types of forced retries.

return ky.retry({code: 'RATE_LIMIT'});
// Resulting error message: 'Forced retry: RATE_LIMIT'

cause

Type: Error

Original error that caused the retry. This allows you to preserve the error chain when forcing a retry based on caught exceptions. The error will be set as the cause of the ForceRetryError, enabling proper error chain traversal.

try {
	const data = await response.clone().json();
	validateBusinessLogic(data);
} catch (error) {
	return ky.retry({
		code: 'VALIDATION_FAILED',
		cause: error  // Preserves original error in chain
	});
}

request

Type: Request

Custom request to use for the retry.

This allows you to modify or completely replace the request during a forced retry. The custom request becomes the starting point for the retry - beforeRetry hooks can still further modify it if needed.

Note: The custom request's signal will be replaced with Ky's managed signal to handle timeouts and user-provided abort signals correctly. If the original request body has been consumed, you must provide a new body or clone the request before consuming.

Example

import ky, {isForceRetryError} from 'ky';

const api = ky.extend({
	hooks: {
		afterResponse: [
			async (request, options, response) => {
				// Retry based on response body content
				if (response.status === 200) {
					const data = await response.clone().json();

					// Simple retry with default delay
					if (data.error?.code === 'TEMPORARY_ERROR') {
						return ky.retry();
					}

					// Retry with custom delay from API response
					if (data.error?.code === 'RATE_LIMIT') {
						return ky.retry({
							delay: data.error.retryAfter * 1000,
							code: 'RATE_LIMIT'
						});
					}

					// Retry with a modified request (e.g., fallback endpoint)
					if (data.error?.code === 'FALLBACK_TO_BACKUP') {
						return ky.retry({
							request: new Request('https://backup-api.com/endpoint', {
								method: request.method,
								headers: request.headers,
							}),
							code: 'BACKUP_ENDPOINT'
						});
					}

					// Retry with refreshed authentication
					if (data.error?.code === 'TOKEN_REFRESH' && data.newToken) {
						return ky.retry({
							request: new Request(request, {
								headers: {
									...Object.fromEntries(request.headers),
									'Authorization': `Bearer ${data.newToken}`
								}
							}),
							code: 'TOKEN_REFRESHED'
						});
					}

					// Retry with cause to preserve error chain
					try {
						validateResponse(data);
					} catch (error) {
						return ky.retry({
							code: 'VALIDATION_FAILED',
							cause: error
						});
					}
				}
			}
		],
		beforeRetry: [
			({error, retryCount}) => {
				// Observable in beforeRetry hooks
				if (isForceRetryError(error)) {
					console.log(`Forced retry #${retryCount}: ${error.message}`);
					// Example output: "Forced retry #1: Forced retry: RATE_LIMIT"
				}
			}
		]
	}
});

const response = await api.get('https://example.com/api');

HTTPError

Exposed for instanceof checks. The error has a response property with the Response object, request property with the Request object, and options property with normalized options (either passed to ky when creating an instance with ky.create() or directly when performing the request).

Be aware that some types of errors, such as network errors, inherently mean that a response was not received. In that case, the error will not be an instance of HTTPError and will not contain a response property.

Important

When catching an HTTPError, you must consume or cancel the error.response body to prevent resource leaks (especially in Deno and Bun).

import {isHTTPError} from 'ky';

try {
	await ky('https://example.com').json();
} catch (error) {
	if (isHTTPError(error)) {
		// Option 1: Read the error response body
		const errorJson = await error.response.json();

		// Option 2: Cancel the body if you don't need it
		// await error.response.body?.cancel();
	}
}

You can also use the beforeError hook:

await ky('https://example.com', {
	hooks: {
		beforeError: [
			async error => {
				const {response} = error;
				if (response) {
					error.message = `${error.message}: ${await response.text()}`;
				}

				return error;
			}
		]
	}
});

⌨️ TypeScript: Accepts an optional type parameter, which defaults to unknown, and is passed through to the return type of error.response.json().

TimeoutError

The error thrown when the request times out. It has a request property with the Request object.

Tips

Sending form data

Sending form data in Ky is identical to fetch. Just pass a FormData instance to the body option. The Content-Type header will be automatically set to multipart/form-data, overriding any existing Content-Type header.

import ky from 'ky';

// `multipart/form-data`
const formData = new FormData();
formData.append('food', 'fries');
formData.append('drink', 'icetea');

const response = await ky.post(url, {body: formData});

If you want to send the data in application/x-www-form-urlencoded format, you will need to encode the data with URLSearchParams. Like FormData, this will override any existing Content-Type headers.

import ky from 'ky';

// `application/x-www-form-urlencoded`
const searchParams = new URLSearchParams();
searchParams.set('food', 'fries');
searchParams.set('drink', 'icetea');

const response = await ky.post(url, {body: searchParams});

Modifying FormData in hooks

If you need to modify FormData in a beforeRequest hook (for example, to transform field names), delete the Content-Type header before creating a new Request:

import ky from 'ky';

const response = await ky.post(url, {
	body: formData,
	hooks: {
		beforeRequest: [
			request => {
				const newFormData = new FormData();

				// Modify FormData as needed
				for (const [key, value] of formData) {
					newFormData.set(key.toLowerCase(), value);
				}

				// Delete `Content-Type` to let Request regenerate it with correct boundary
				request.headers.delete('content-type');

				return new Request(request, {body: newFormData});
			}
		]
	}
});

Setting a custom `Content-Type`

Ky automatically sets an appropriate Content-Type header for each request based on the data in the request body. However, some APIs require custom, non-standard content types, such as application/x-amz-json-1.1. Using the headers option, you can manually override the content type.

import ky from 'ky';

const json = await ky.post('https://example.com', {
	headers: {
		'content-type': 'application/json'
	},
	json: {
		foo: true
	},
}).json();

console.log(json);
//=> {data: '🦄'}

Cancellation

Fetch (and hence Ky) has built-in support for request cancellation through the AbortController API. Read more.

Example:

import ky from 'ky';

const controller = new AbortController();
const {signal} = controller;

setTimeout(() => {
	controller.abort();
}, 5000);

try {
	console.log(await ky(url, {signal}).text());
} catch (error) {
	if (error.name === 'AbortError') {
		console.log('Fetch aborted');
	} else {
		console.error('Fetch error:', error);
	}
}

Proxy support (Node.js)

Native proxy support

Node.js 24.5+ supports automatic proxy configuration via environment variables. Set NODE_USE_ENV_PROXY=1 or use the --use-env-proxy CLI flag.

NODE_USE_ENV_PROXY=1 HTTP_PROXY=http://proxy.example.com:8080 node app.js

Or:

node --use-env-proxy app.js

Supported environment variables:

HTTP_PROXY / http_proxy: Proxy URL for HTTP requests
HTTPS_PROXY / https_proxy: Proxy URL for HTTPS requests
NO_PROXY / no_proxy: Comma-separated list of hosts to bypass the proxy

Using ProxyAgent

For more control, use ProxyAgent or EnvHttpProxyAgent with the dispatcher option.

import ky from 'ky';
import {ProxyAgent} from 'undici';

const proxyAgent = new ProxyAgent('http://proxy.example.com:8080');

const response = await ky('https://example.com', {
	// @ts-expect-error - dispatcher is not in the type definition, but it's passed through to fetch.
	dispatcher: proxyAgent
}).json();

Using EnvHttpProxyAgent to automatically read proxy settings from environment variables:

import ky from 'ky';
import {EnvHttpProxyAgent} from 'undici';

const proxyAgent = new EnvHttpProxyAgent();

const api = ky.extend({
	// @ts-expect-error - dispatcher is not in the type definition, but it's passed through to fetch.
	dispatcher: proxyAgent
});

const response = await api('https://example.com').json();

HTTP/2 support (Node.js)

Undici supports HTTP/2, but it's not enabled by default. Create a custom dispatcher with the allowH2 option:

import ky from 'ky';
import {Agent, Pool} from 'undici';

const agent = new Agent({
	factory(origin, options) {
		return new Pool(origin, {
			...options,
			allowH2: true
		});
	}
});

const response = await ky('https://example.com', {
	// @ts-expect-error - dispatcher is not in the type definition, but it's passed through to fetch.
	dispatcher: agent
}).json();

Combine proxy and HTTP/2:

import ky from 'ky';
import {ProxyAgent} from 'undici';

const proxyAgent = new ProxyAgent({
	uri: 'http://proxy.example.com:8080',
	allowH2: true
});

const response = await ky('https://example.com', {
	// @ts-expect-error - dispatcher is not in the type definition, but it's passed through to fetch.
	dispatcher: proxyAgent
}).json();

Consuming Server-Sent Events (SSE)

Use parse-sse:

import ky from 'ky';
import {parseServerSentEvents} from 'parse-sse';

const response = await ky('https://api.example.com/events');

for await (const event of parseServerSentEvents(response)) {
	console.log(event.data);
}

Extending types

Ky's TypeScript types are intentionally defined as type aliases rather than interfaces to prevent global module augmentation, which can lead to type conflicts and unexpected behavior across your codebase. If you need to add custom properties to Ky's types like KyResponse or HTTPError, create local wrapper types instead:

import ky, {HTTPError} from 'ky';

interface CustomError extends HTTPError {
	customProperty: unknown;
}

const api = ky.extend({
	hooks: {
		beforeError: [
			async error => {
				(error as CustomError).customProperty = 'value';
				return error;
			}
		]
	}
});

// Use with type assertion
const data = (error as CustomError).customProperty;

This approach keeps your types scoped to where they're needed without polluting the global namespace.

FAQ

How do I use this in Node.js?

Node.js 18 and later supports fetch natively, so you can just use this package directly.

How do I use this with a web app (React, Vue.js, etc.) that uses server-side rendering (SSR)?

Same as above.

How do I test a browser library that uses this?

Either use a test runner that can run in the browser, like Mocha, or use AVA with ky-universal. Read more.

How do I use this without a bundler like Webpack?

Make sure your code is running as a JavaScript module (ESM), for example by using a <script type="module"> tag in your HTML document. Then Ky can be imported directly by that module without a bundler or other tools.

<script type="module">
import ky from 'https://unpkg.com/ky/distribution/index.js';

const json = await ky('https://jsonplaceholder.typicode.com/todos/1').json();

console.log(json.title);
//=> 'delectus aut autem'
</script>

How is it different from `got`

Got is maintained by the same people as Ky, so you probably want Ky instead. It's smaller, works in the browser too, and is more stable since it's built on Fetch.

How is it different from `axios`?

See my answer here.

How is it different from `r2`?

See my answer in #10.

What does `ky` mean?

It's just a random short npm package name I managed to get. It does, however, have a meaning in Japanese:

A form of text-able slang, KY is an abbreviation for 空気読めない (kuuki yomenai), which literally translates into “cannot read the air.” It's a phrase applied to someone who misses the implied meaning.

Browser support

The latest version of Chrome, Firefox, and Safari.

Node.js support

Node.js 18 and later.

Related

fetch-extras - Useful utilities for working with Fetch
ky-hooks-change-case - Ky hooks to modify cases on requests and responses of objects

Maintainers