BundlePhobia

Free online tool that shows the real minified and gzipped bundle cost of any npm package. Check size over version history, identify tree-shakeable packages, find smaller alternatives, and estimate download times — all before writing a single npm install.

What is BundlePhobia?

BundlePhobia is a free public web tool created by Paskal Rao that answers the question every developer should ask before installing a dependency: how much does this package actually cost? You type in any npm package name, and BundlePhobia builds it in isolation, measures the output, and presents a clear breakdown of the minified size, gzipped size, download time on various connection speeds, and whether the package supports tree shaking.

The tool is especially valuable when choosing between competing libraries. A quick search for moment versus date-fns versus dayjs immediately shows that moment ships 18 kB gzipped with no tree shaking, while dayjs delivers the same core API for 2.8 kB. That is the kind of information that should drive dependency decisions, and BundlePhobia surfaces it in seconds without requiring any local setup.

Key Features

• Minified + gzipped size — reports both the post-minification size and the compressed size that browsers actually download
• Version history — a chart showing how package size has changed across every published version, highlighting when a package bloated
• Tree-shaking flag — shows whether the package declares sideEffects: false, meaning unused exports can be removed by bundlers
• Download time estimates — projected download time on slow 3G, 4G, and other connection profiles for real-world context
• Smaller alternatives — automatically suggests lighter packages with similar functionality for common dependencies
• Duplicate dependency detection — warns if a package bundles a dependency you already have, signaling potential size duplication
• Public JSON API — a free REST endpoint for programmatic size lookups, no API key required
• No install needed — entirely online, works from any browser, nothing to configure locally

How to Use BundlePhobia

# No installation needed — just visit:
# https://bundlephobia.com/

# Search for any npm package by name in the search bar, e.g.:
#   moment
#   lodash
#   date-fns
#   axios
#   react-query

# Or navigate directly to a package result:
# https://bundlephobia.com/package/lodash
# https://bundlephobia.com/package/date-fns
# https://bundlephobia.com/package/[email protected]

# To check a specific version, append @version to the package name in the URL.

Understanding the Results

Each result page shows multiple signals. Understanding what each number means helps you make the right decision about whether to add, replace, or avoid a package.

# Understanding what BundlePhobia shows you

# For each package, BundlePhobia displays:
#
# 1. MINIFIED SIZE — after removing whitespace and comments
#    Example: lodash = 531 kB minified
#
# 2. GZIPPED SIZE — what the browser actually downloads
#    Example: lodash = 71.7 kB gzipped
#
# 3. VERSION HISTORY — a chart of size changes across versions
#    Useful for spotting when a package ballooned in size
#
# 4. DOWNLOAD TIME ESTIMATES — slow 3G / 4G / emerging markets
#    Example: lodash 71 kB = ~1.4 s on slow 3G
#
# 5. SIMILAR PACKAGES — smaller alternatives with size comparison
#    lodash → alternatives: lodash-es, just, remeda, radash
#
# 6. DUPLICATE DETECTION — warns if the package brings in a dependency
#    you already have (e.g. a package bundling its own copy of React)
#
# 7. SIDE EFFECTS FLAG — whether tree shaking can remove unused exports
#    hasSideEffects: false = safe to tree shake
#    hasSideEffects: true  = entire package loads regardless of imports

Practical Example: Choosing a Date Library

BundlePhobia excels at comparative evaluations. Here is a real-world workflow for choosing a date handling library.

# Example workflow: evaluating a date library before adding it as a dependency

# Step 1: Visit bundlephobia.com and search for "moment"
# Result: [email protected] — 72.1 kB (minified) / 18.2 kB (gzip)
# Warning: hasSideEffects: true (cannot tree-shake)
# Shows: download time ~364 ms on slow 3G

# Step 2: Search for alternatives Bundlephobia suggests: "date-fns"
# Result: [email protected] — 2.28 kB for a single import (tree-shakeable!)
# The full package is 500+ kB but you only pay for what you import.

# Step 3: Check "dayjs"
# Result: [email protected] — 6.96 kB (minified) / 2.77 kB (gzip)
# hasSideEffects: false (tree-shakeable)

# Conclusion: moment costs 18.2 kB gzipped on every load.
# date-fns or dayjs are 4-8x smaller for equivalent functionality.

Using the Public API

BundlePhobia exposes a free JSON API for programmatic lookups. Useful for automated dependency audits or custom tooling.

# BundlePhobia also exposes a public JSON API — no API key required.

# Get bundle size info for a package
curl "https://bundlephobia.com/api/size?package=lodash"

# Response (abbreviated):
# {
#   "name": "lodash",
#   "version": "4.17.21",
#   "description": "Lodash modular utilities.",
#   "size": 531614,
#   "gzip": 71655,
#   "dependencyCount": 0,
#   "hasSideEffects": true,
#   "hasJSModule": false,
#   "hasJSNext": false,
#   "isModuleType": false
# }

# Get size for a specific version
curl "https://bundlephobia.com/api/[email protected]"

# Get size history across all versions
curl "https://bundlephobia.com/api/size-history?package=axios"

Editor and Workflow Integrations

Beyond the website, BundlePhobia data is available through editor extensions and can be queried via the API to build custom auditing workflows.

# Using Bundlephobia data in your workflow

# 1. Browser extension (unofficial) — shows package size inline on
#    npmjs.com and github.com package listings

# 2. VS Code extension — bundlephobia-vscode shows import sizes inline
#    in your editor as you type import statements:
#    import { format } from 'date-fns';  // 17 B

# 3. Package.json audit — manually cross-check your top dependencies:
#    cat package.json | grep -E '"[^"]+": "^' | while read line; do
#      pkg=$(echo "$line" | cut -d'"' -f2)
#      echo "Checking: $pkg"
#      curl -s "https://bundlephobia.com/api/size?package=$pkg" |
#        python3 -c "import sys,json; d=json.load(sys.stdin);
#          print(d['name'], d['gzip'], 'bytes gzipped')"
#    done

BundlePhobia vs Size Limit vs Bundlewatch

Pros and Cons