Brotli compression quality comparison in the real world

1 December 2021   1 comment   Node, JavaScript

At work, we use Brotli (using the Node builtin zlib) to compress these large .json files to files. When using zlib.brotliCompress you can set options to override the quality number. Here's an example of it at quality 6:

import { promisify } from 'util'
import zlib from 'zlib'
const brotliCompress = promisify(zlib.brotliCompress)

const options = {
  params: {
    [zlib.constants.BROTLI_PARAM_MODE]: zlib.constants.BROTLI_MODE_TEXT,
    [zlib.constants.BROTLI_PARAM_QUALITY]: 6,

export async function compress(data) {
  return brotliCompress(data, options)

But what if you mess with that number. Surely, the files will become smaller, but at what cost? Well, I wrote a Node script that measured how long it would take to compress 6 large (~25MB each) .json file synchronously. Then, I put them into a Google spreadsheet and voila:


Total size per level


Total seconds per level

Miles away from rocket science but I thought it was cute to visualize as a way of understanding the quality option.



That's super interesting! So if time and compute is not a limiting issue one can get quite some smaler files!
I wonder if this this impacts decompression in any way? 🤔

Your email will never ever be published.

Related posts