Bundle Size Estimator
Estimate JavaScript bundle size after tree-shaking with gzip and brotli compression estimates.
How it works
- 1Enter your values in the fields above
- 2Click "Estimate" — all math runs in your browser
- 3View your results instantly
What to do next
About Bundle Size Estimator
Bundle Size Estimator is a developer tool that runs in your browser. Estimate JavaScript bundle size after tree-shaking with gzip and brotli compression estimates. The page you are reading is the same workspace you will use to do the work: pick a file or paste your input, choose the options that matter to you, and the tool produces the result on your device.
Bundle Size Estimator runs on standard browser APIs — an open-source, well-audited engine that performs the developer utility natively in the browser. It accepts the formats listed in the upload area and produces output that opens in any standard developer viewer. Per-run input is capped at 0 MB.
Bundle Size Estimator is shaped around the recurring needs of two audiences: devops engineers crafting one-liners, who use it as a quick utility between bigger tools, and engineers debugging API payloads, who use it as their primary way of getting the job done. Both groups get the same defaults and the same speed.
The browser sandbox isolates the page's JavaScript from the rest of the system, the same way it isolates every other tab you have open. Bundle Size Estimator works inside that sandbox: it reads the file you give it, processes it with standard browser APIs, and writes the result back. Nothing leaves the page's memory unless you choose to download or copy it.
Most people land on Bundle Size Estimator via a search at the moment they actually need the tool. That shapes the design: the page is a single screen with the input on one side, the controls in the middle, and the result on the other, so a first-time visitor can complete the job without reading documentation.
Once the engine finishes, the output is offered as an immediate download. There is no preview gate, no email-wall, and no "register to download" intermediary — the file is yours the moment it is ready.
Constraints worth knowing about: inputs are capped at 0 MB to keep memory usage in a sensible range, one input is processed per run, and the tool must be loaded over HTTPS for the in-browser engine to work. These are properties of the architecture.
For multi-step jobs, Bundle Size Estimator sits next to Web Performance Calculator, File Size Converter, and Load Testing Calculator. None of them depend on each other — you can use Bundle Size Estimator on its own — but together they cover the common variations of the task this page exists to handle.
Bundle Size Estimator is honest about scope: it handles a single, well-defined developer utility step. Specialist edge-case work — uncommon formats, very large inputs, or pipelines that need scripting — is what dedicated desktop apps are for. This page handles the common case quickly.
Bundle Size Estimator is one example of a broader pattern: utility software increasingly works as single-page, client-side experiences. Every page in the catalog is shaped that way, which keeps each tool fast to load and easy to recommend in a single link.
Bundle Size Estimator fits the gap where opening a desktop app feels heavy and writing a script feels overkill. The page handles the common developer utility task with sensible defaults so a single visit usually completes the job; for highly specialised work, a dedicated desktop application can offer more knobs to turn.
Pro tip: Bundle Size Estimator works just as well in a private/incognito window as in a normal one, which is occasionally useful when you want zero browser-history footprint of the job. Another tip: if the tool ever feels slow, it is almost always because the browser tab is competing for CPU with another tab — pausing or closing the heavy ones gives the engine room to work.
Common gotchas worth flagging: the supported formats are listed in the upload area. The 0 MB ceiling is per-file, not per-session; you can run as many separate jobs as you like, but a single oversized input will be rejected on load.
If Bundle Size Estimator solved your problem, sharing the page link with someone who has the same problem is the most useful thing you can do. The catalog grows mostly through word of mouth; visitors arriving through a recommendation tend to be the ones the tool serves best.
How it works
- 1Land on the Bundle Size Estimator page. The tool is ready to use the moment the page renders.
- 2Add your developer input by dropping it onto the page or browsing for it.
- 3Tweak the controls if the defaults are not quite right for your input. The options are kept short and labelled in plain language.
- 4Click to start the job. The engine (standard browser APIs) processes the input in the page; you can watch the progress indicator until it completes.
- 5Grab the output as soon as the run completes. You can also copy the result instead of downloading if the next tool in your workflow accepts pasted input.
- 6Repeat the process for additional inputs whenever you need to. The page stays loaded, so subsequent runs are quick.
Common use cases
- Generate boilerplate from a single specification line using Bundle Size Estimator.
- Validate a config blob before pushing to staging.
- Pretty-print a minified blob during incident triage.
- Hash a string for a quick reproducibility check.
- Inspect a regex against a test string before committing it.
- Decode a token to confirm its claims during a debugging session.
- Convert between data formats while wiring up an integration.
- Compare two API responses to spot a regression.
- Generate a quick fixture without leaving the browser.
- Encode binary content for transport in a JSON body.
FAQ
Where do I get dependency sizes?
Check bundlephobia.com for package sizes, or use your build tool's bundle analysis output.
Tree-shaking accuracy?
The tree-shaking percentage is an estimate; actual reduction depends on import patterns and bundler.
Gzip vs brotli?
Gzip typically compresses to ~30% of original; brotli to ~22%. Actual ratios vary by content.
Private?
Yes — calculations run locally.
Multiple bundles?
This estimates a single bundle; run separately for each chunk in code-split apps.
Warning threshold?
Bundles over 500 KB (after tree-shaking) trigger a code-splitting suggestion.
Can I call Bundle Size Estimator from a script?
Bundle Size Estimator is a browser-only tool by design and does not expose a hosted API. The reason is the same as the privacy story: there is no Favtoo backend doing the work, so there is no service to call. If you need to script the same transformation, the underlying engine (standard browser APIs) is open-source and can be used directly from your own code.
Does Favtoo keep a copy of files I process with Bundle Size Estimator?
Favtoo keeps no copy of your file because Favtoo never receives your file. Bundle Size Estimator runs entirely in your browser, the input is held only in your tab's memory, and closing the tab discards it. There is no opt-in cloud history, no "recent jobs" panel synced to an account, and no server-side retention to configure — the architecture simply has nowhere for your file to be stored.
Does Bundle Size Estimator work on a phone or tablet?
Bundle Size Estimator runs in any modern mobile browser — Safari, Chrome, Firefox and the in-app browsers in most messaging apps all support the underlying APIs. Performance depends on the device: a recent phone handles typical inputs nearly as fast as a laptop, while older devices may take a few seconds longer near the 0 MB ceiling. The interface lays out cleanly on small screens, so you do not need to pinch-zoom to see the controls.
Does Bundle Size Estimator match what professional tools produce?
Bundle Size Estimator is built on standard browser APIs, which is the same class of engine used by professional developer utility pipelines. For deterministic operations, the output is byte-identical to what an equivalent CLI run would produce; for operations involving a codec or a model, the result is well within the range of what comparable tools generate. If you have a specific reference output you need to match, run a small test job first to confirm the configuration produces what you expect.
Does Bundle Size Estimator work in Safari, Firefox, Chrome and Edge?
Bundle Size Estimator works in any modern browser released in the last few years — Chrome, Edge, Firefox, Safari, Brave, Arc and the major Chromium derivatives are all supported. The underlying engine relies on widely-supported web APIs, so there is nothing exotic to install. If you are on a very old browser version and the tool fails to load, updating to the latest release of your preferred browser is the only fix needed.
What does Bundle Size Estimator do that command-line tools do not?
Desktop apps usually have more advanced features but require installation, maintenance and (often) a licence. Paid online tools are convenient but route your file through their servers and gate downloads behind accounts. Bundle Size Estimator sits in between: free, instant, and private, but intentionally narrow in scope. For one-off jobs and the common developer utility operations, it is usually the lowest-friction choice; for highly specialised work, a dedicated app is still the right answer.
What does the error message in Bundle Size Estimator mean?
Failures usually fall into one of three buckets: the input is in an unsupported format, the input is over the size cap, or the input is structurally malformed (a truncated download, a partial export, or a stream the engine does not recognise). The first two are easy to confirm — check that your file is in a supported format and that it is below 0 MB. For the third, opening the file in its native viewer first is the fastest way to confirm the source is intact.
How do I run Bundle Size Estimator over a folder of files?
Bundle Size Estimator processes one input at a time by design — it keeps memory usage predictable on lower-end devices and makes results easier to verify. To handle a folder, run the tool once per file; the page stays loaded between runs and remembers your last-used settings, so the second run is essentially instant.
How do I know I am using the latest version of Bundle Size Estimator?
Bundle Size Estimator is updated whenever the underlying engine releases an improvement or a bug fix. Because the tool is delivered as a static page, every visit fetches the latest version automatically — there is no "version" to manage on your end. If a particular release ever changes default behaviour, the change is documented on Favtoo's changelog so you can confirm what shifted.