TypeScript icon, indicating that this package has built-in type declarations

2.0.0 • Public • Published

npm version downloads build status coverage status


Get the mime type of a stream by inspecting its header. The stream is being consumed, but a new readable stream is returned together with the mime type.

Supports both Node.js ReadableStream (of Buffers, not object-mode) and Streams API ReadableStream of typed arrays (such as e.g. Uint8Array), ArrayBuffers or DataViews.

The first couple of kilobytes are necessary to deduce the filetype. After that, the returned promise is resolved with a new stream (from the beginning of the input stream) and the mime type.

It also supports buffers (of type Uint8Array, such as Node.js Buffers) and file descriptors instead of streams.


From v2:

  • This package is a pure ESM, no CommonJS support


getMimeType takes either a number (file descriptor), a buffer (Uint8Array) or a readable stream as first argument. The returned promise contains the mime type and a new readable stream (if the input was a stream) for further streaming, on the form:

interface ReturnType {
    stream: ReadableStream; // If the input was a stream, otherwise undefined
    mime: string;

To aid finding the mime-type if it is unclear given the content of the stream (or buffer or file descriptor), a filename can be provided, in which case a mime-type can be deduced as a fallback.


getMimeType( stream | buffer | fd, opts? ): Promise<ReturnType>;

Stream example

import { getMimeType } from 'stream-mime-type'

let inStream: NodeJS.ReadableStream; // Get from somewhere
const { stream, mime } = await getMimeType( inStream );

console.log(mime); // e.g. 'image/png'
stream.pipe(outStream); // Keep streaming

Buffer example

import { readFileSync } from 'fs'
import { getMimeType } from 'stream-mime-type'

const imageBuffer = readFileSync("file.png", null); // Returns a Buffer
const { mime } = await getMimeType( imageBuffer, { filename: "file.png" } );

console.log(mime); // 'image/png'

File descriptor

import { openSync } from 'fs'
import { getMimeType } from 'stream-mime-type'

const fd = openSync("file.png", "r");
const { mime } = await getMimeType( fd, { filename: "file.png" } );

console.log(mime); // 'image/png'


The second argument to getMimeType is an options object on the format:

interface GetMimeTypeOptions {
    strict?: boolean;
    filename?: string;

The filename can provide a hint to the content type if it's not found by the file contents.

The strict can be set to true (defaults to false) in which case the result will not fallback to application/octet-stream if no other mime type was found. The return value will be undefined instead.


npm i stream-mime-type

DownloadsWeekly Downloads






Unpacked Size

9.77 kB

Total Files


Last publish


  • grantila