Web Font Detector — Font Detection Script
Generate a JavaScript snippet that detects installed system fonts and loaded web fonts on the current page.
How it works
- 1Configure your options above
- 2Click "Generate Detection Script" — processing happens in your browser
- 3Copy or download the result
What to do next
About Web Font Detector
Web Font Detector is a web utility tool that runs in your browser. Generate a JavaScript snippet that detects installed system fonts and loaded web fonts on the current page. 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.
Web Font Detector sees the most use from analysts pulling lightweight reports and community managers planning posts, but the design is intentionally generic enough that you do not need a specialist background to get a good result. The defaults aim at the most common case so a first-time user can get the right output without changing any settings.
The right moment to reach for Web Font Detector is when you have a focused web and productivity utility job that fits inside a browser tab. Open the page, drop in the file or paste your input, choose the options that matter, and the tool returns the result.
Web Font Detector runs on standard browser APIs — an open-source, well-audited engine that performs the web and productivity utility natively in the browser. It accepts the formats listed in the upload area and produces output that opens in any standard web utility viewer. Per-run input is capped at 0 MB.
The architecture is local-first by design. Once the page is loaded, you can disconnect from the network and the tool still completes the job. The processing stack — standard browser APIs and the small UI shell wrapping it — ships with the page itself, so the tool keeps working in offline conditions, on a captive-portal Wi-Fi, or behind a corporate proxy that limits what the tab can reach.
Web Font Detector sits in a small group of related tools. Useful neighbours include CSS Support Checker, JS Support Checker, Browser Feature Detector, and Browser Info Detector. They are designed to compose: the output of one is a sensible input to the next, so a multi-step task is usually a sequence of single-click operations.
The only practical limit is the 0 MB per-file ceiling, which keeps the tool responsive across a wide range of devices. Run the tool ten times in a row, run it ten thousand times — it behaves the same way and produces the same quality of result.
Web Font Detector is built around steady iteration on a small set of options rather than feature creep. Every additional setting attracts a slightly different audience, but a long settings panel makes the common case slower for everyone. The current controls reflect what users of the tool actually use.
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.
From a product perspective, Web Font Detector is one of the simplest possible expressions of "do one thing well." The catalog contains dozens of related tools that each handle a slightly different web and productivity utility task, and every one is a separate page rather than a tab inside a larger app. That separation keeps each tool fast to load and easy to bookmark.
Web Font Detector fits the gap where opening a desktop app feels heavy and writing a script feels overkill. The page handles the common web and productivity 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: Web Font Detector 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.
That is essentially everything Web Font Detector does and how it does it. Open the tool above, drop in your input, and the work happens in the page. If you find yourself reaching for it often, bookmark the page — it loads quickly on subsequent visits, and your most-recent settings are remembered for the rest of the session.
How it works
- 1Open Web Font Detector in your browser. The page loads quickly and the tool is ready to use the moment it becomes interactive.
- 2Add your web utility 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.
- 5Download the result. The file is generated in your browser and saved through your normal download flow.
- 6Run additional jobs as needed. The same controls and defaults apply on every run.
Common use cases
- Sanity-check a webhook response while debugging using Web Font Detector.
- Run a fast accessibility check before publishing.
- Plan content without paying for a SaaS dashboard.
- Generate a temporary asset for a social post.
- Run a one-off check during a meeting without context-switching.
- Pull a quick reference number for a status update.
- Audit a marketing page before launch.
- Create a placeholder image for a wireframe.
- Validate a setting before circulating it to a team.
- Compare two product variations side by side.
FAQ
How does it work?
Creates a hidden span element and compares rendered widths against base fonts to detect availability.
Which fonts are tested?
35+ fonts including system fonts (Arial, Helvetica), developer fonts (Fira Code, JetBrains Mono), and web fonts.
Web fonts vs system?
System fonts are detected by width comparison. Loaded web fonts are listed via document.fonts API.
Private?
Yes — runs locally. No font data is sent externally.
Fingerprinting?
Font detection can be used for fingerprinting. Browsers are increasingly restricting the fonts API.
Custom fonts?
Add your custom font names to the fontsToTest array in the generated script.
Can I use Web Font Detector offline?
Once the page is loaded, Web Font Detector can complete jobs without an active internet connection — the engine is bundled with the page, so there is no per-job network call. The initial page load does require a connection (to fetch the static assets), but after that you can disconnect entirely and the tool will still work. This is a side-effect of the local-first architecture, not a deliberate "offline mode" feature.
How do I run Web Font Detector over a folder of files?
Web Font Detector 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.
Are jobs run with Web Font Detector stored anywhere?
Favtoo keeps no copy of your file because Favtoo never receives your file. Web Font Detector 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.
Is Web Font Detector mobile-friendly?
Web Font Detector 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.
Are there any restrictions on using Web Font Detector at work?
Web Font Detector can be used for personal and commercial work alike — there is no separate "business" licence to purchase. The output you generate is yours to use however you want, including in client deliverables, internal documents, or commercial products. Favtoo's only ask is fair, individual use; the tool is not designed to be embedded as a backend service or wrapped behind an API for resale.
Why is my browser prompting me when I open Web Font Detector?
Web Font Detector only needs the standard web platform — file picker access for the inputs you choose to load, and optionally clipboard access if you copy the result rather than downloading it. There is no microphone, camera, geolocation or background-permission request, because none of those are needed for the work the tool does.
Is the source for Web Font Detector available?
Web Font Detector is a static page running an open-source engine in your browser, so a typical corporate firewall does not get in the way as long as it allows JavaScript to load from Favtoo. For teams that need to host it themselves on an internal network, the underlying engine (standard browser APIs) is open-source and can be packaged into a private build with the same behaviour. Reach out via the Contact page if that is something you are exploring.
Can I call Web Font Detector from a script?
Web Font Detector 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.
Will Web Font Detector ask me to pay to download the result?
Web Font Detector is free to use. The processing runs in your browser, which keeps the per-user cost low enough that the tool can be offered openly. The download is the same file the engine produced — you can use it for as many runs as you need.