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Harold avatar: Sad emoji with a smile mask on a face


Harold is a CLI tool that compares frontend project bundles in size.



The bundle size of an average frontend project grows on every change.

To feel the pain To make it easier to measure & compare the project size while refactoring or updating the deps, we've built Harold.


Demo GIF

The demo is accelerated. In real life setting up the dependencies and building a project takes forever.


npm install -g @funboxteam/harold


snapshot [options]

Builds the project and takes the snapshot.

Available options:

  • -o, --output <path> — sets the snapshot output path; default is harold_snapshot_<date>_<time>.json;
  • -e, --exec <cmd> — sets the building command; default is npm run build-production. The command will be run with NO_HASH=true env variable set;
  • -p, --path <path> — sets the path of the build result directory, which will be used for snapshotting; default is public.

diff <left> <right>

Compares the passed snapshots.


Sends halp.


How does it work?

When you take a snapshot, Harold runs the build command, waits until the project is building, then goes to the output directory and records the files' sizes. At the same time it creates the gzipped version of each file and records it's size too. After than it spits the snapshot — JSON file with all the data.

Then, when you have two snapshots and run harold diff first.json second.json it compares the diff files and prints the overall comparison.

Usage example
# Open your project folder
$ cd ~/my-syper-kewl-project/

# Take the first snapshot
$ harold snapshot -o before.json

# Make some changes in the project

# Take the second snapshot
$ harold snapshot -o after.json

# Compare them
$ harold diff before.json after.json

 Left: 11/10/2020 6:30:56 PM • my-syper-kewl-project • master
 Right: 11/10/2020 6:45:13 PM • my-syper-kewl-project • improvement/framework-update

Build time:
 16 seconds slower (Left: 129 seconds, Right: 145 seconds)

Diff by category:
                before              after               Changes
  JS            1.04 MB (270 kB)    1.12 MB (294 kB)    +78.2 kB (+23.7 kB), +1 item
  JS (legacy)   1.07 MB (285 kB)    1.16 MB (314 kB)    +90.6 kB (+28.6 kB), +1 item
  CSS           144 kB (23.4 kB)    144 kB (23.4 kB)    No changes
  Images        5.26 MB (5.23 MB)   5.26 MB (5.23 MB)   No changes
  Fonts         159 kB (159 kB)     159 kB (159 kB)     No changes
  Videos        1.59 MB (1.58 MB)   1.59 MB (1.58 MB)   No changes
  Other         127 kB (13.2 kB)    127 kB (13.3 kB)    +364 B (+82 B)

  Total         9.4 MB (7.56 MB)    9.57 MB (7.61 MB)   +169 kB (+52.4 kB), +2 items

Diff by files:
 m public: +169 kB (+52.4 kB)
 m public/10.js: +16 B (+4 B)
 m public/11.js: -20 B (-3 B)
 + public/12.js: 301 B (143 B)
 m public/3.js: +1.84 kB (+621 B)
 m public/app.js: +4.18 kB (+843 B)
 m public/legacy.10.js: +42 B (+18 B)
 + public/legacy.12.js: 513 B (148 B)
 m public/legacy.3.js: +1.9 kB (+634 B)
 m public/ +6.83 kB (+1 kB)
 m public/legacy.vendor.js: +81.3 kB (+26.8 kB)
 m public/legacy.vendor.js.LICENSE: +182 B (+41 B)
 m public/vendor.js: +72.2 kB (+22.1 kB)
 m public/vendor.js.LICENSE: +182 B (+41 B)

What is NO_HASH?

Modern frontend bundlers may add hashes to the filenames to improve caching. But Harold compares files using their names. To improve the diff quality you should set up your bundler the way that turns off hashes when NO_HASH set.

Or you may just provide another env variable if you need:

WITHOUT_CONTENTHASH=true harold snapshot

How to make a snapshot without building a project?

Pass to --exec a fake command, such as echo 1.

What is “JS (legacy)”?

Due to the variety of web browsers, nowadays frontenders have to support not only modern Chrome & Firefox, but also old dusty IE or Presto-based Opera. To make it easier for users with modern browsers to download assets, developers split the bundle on two parts: modern one & legacy one. The latter includes more polyfills, contains older JS syntax, etc.

Harold expects that in the case of legacy bundle existence, its files will be named as legacy.*.js. If there are such files, their stat will appear in “JS (legacy)” row.


The avatar for the project was made by Igor Garybaldi.

Sponsored by FunBox


Compares frontend project bundles







Contributors 4