Prime Number Generator — Primes in a Range
List primes in a numeric range using efficient sieving with progress for medium-sized bounds.
How it works
- 1Configure your options above
- 2Click "Generate" — processing happens in your browser
- 3Copy or download the result
What to do next
About Prime Number Generator
Prime Number Generator runs the web and productivity utility job locally inside your browser. List primes in a numeric range using efficient sieving with progress for medium-sized bounds. The work happens on your machine, the result is generated on your machine, and the page exposes the controls you need to drive it without burying them in menus.
Prime Number Generator is implemented on top of standard browser APIs. Inputs are read from the file picker or drop zone, decoded in the browser, processed, and re-encoded into the output format. Files up to 0 MB are well within the comfort zone of any modern browser.
Prime Number Generator parses your file with standard browser APIs entirely inside the browser, applies the options you selected, and returns a download. The processing has no network step, which means a slow or intermittent connection does not slow down the work — once the page is loaded, only your CPU and RAM are involved.
Typical users of Prime Number Generator include product managers comparing options, teachers building resource lists and site owners auditing pages. The thread connecting all of them is the same: a focused web and productivity utility task that fits cleanly into a browser tab and benefits from a tool with sensible defaults and minimal setup.
Prime Number Generator works well as a bookmarked utility you reach for when you need it. The first visit shows you what the tool does; the second is when you realise it is a low-friction option for the task and worth keeping in your tab list.
The hard constraints are easy to remember. Maximum input: 0 MB. Multiple files per run: no — one input at a time, by design, to keep results predictable. The same controls apply on every run.
As a workflow component, Prime Number Generator is the part you reach for when a single, well-defined web and productivity utility step needs to happen. It performs that step and returns a standard file you can carry into the next part of your pipeline.
Prime Number Generator keeps the control set focused. Every option on the page is there because a real workflow needs it, and the defaults aim at the most common case so a first-time user can get the right output without changing any settings.
Prime Number Generator returns the result as a download. If you are running multiple jobs, the output names will not collide as long as the input names differ. You can re-run with different settings as many times as you like; each run produces a fresh file with no caching trickery in between.
Some background on the design choices behind Prime Number Generator: every option you see on the page is there because a real workflow needs it, and every option that is not shown has been deliberately omitted to keep the common case fast. The bias is toward minimal-but-complete.
Prime Number Generator produces deterministic output: the same input plus the same options always produces the same result. That predictability matters when the result has to match an upstream specification or be reproducible later.
Pro tip: Prime Number Generator 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.
For most failure modes, refreshing the page and re-running the job is enough — the engine has no persistent state to corrupt. If the same input fails twice in a row, the input itself is most likely the problem (a truncated file, an unexpected variant of the format, or a stream the engine does not recognise).
Prime Number Generator is intentionally narrow in scope so the common case is fast and the result is predictable. If you ever need a variation it does not cover, browse the rest of the catalog — there is a good chance an adjacent tool already exists, and switching between tools is just a matter of opening another tab.
How it works
- 1Reach the Prime Number Generator page in your browser to begin.
- 2Add your web utility input by dropping it onto the page or browsing for it.
- 3Adjust the options to match what you need. Sensible defaults cover the most common case, so you can usually skip this step.
- 4Trigger processing. standard browser APIs reads your input, applies the transformation, and writes the result back into the page.
- 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.
- 6Run additional jobs as needed. The same controls and defaults apply on every run.
Common use cases
- Pull a quick reference number for a status update using Prime Number Generator.
- Sanity-check a webhook response while debugging.
- Run a fast accessibility check before publishing.
- Generate a campaign asset in seconds for a quick test.
- Validate a setting before circulating it to a team.
- Run a one-off check during a meeting without context-switching.
- Generate a temporary asset for a social post.
- Create a placeholder image for a wireframe.
- Compare two product variations side by side.
FAQ
What is the practical upper bound?
Millions of primes are feasible; pushing past ~1e8 may exhaust memory depending on hardware.
Which algorithm is used?
Segmented sieve of Eratosthenes minimizes memory while scanning contiguous ranges.
Can I test if one number is prime?
Set the range to that single value for a deterministic yes/no with trial division fallback.
Does it parallelize?
Single-threaded for simplicity; split ranges manually if you need multi-core throughput.
Is my range private?
Yes — the sieve array is allocated locally; we never see which bounds you choose.
Which browsers are supported?
Typed arrays speed sieves in Chrome, Firefox, Safari, and Edge on 64-bit systems.
Are there any restrictions on using Prime Number Generator at work?
Prime Number Generator 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.
Does Prime Number Generator require a browser extension or plug-in?
No installation is needed. Prime Number Generator runs as a normal web page, with no browser extension, no native helper, and no separate desktop client to download. That is partly a privacy choice — extensions can request broad permissions, while a regular page is sandboxed by default — and partly a convenience one: you can use Prime Number Generator on any computer you have temporary access to without leaving anything installed on it.
Which file formats does Prime Number Generator accept?
The accepted formats are listed in the upload area on the tool itself. If your input is in a format that is not directly supported, convert it first using one of Favtoo's converter tools — every Favtoo converter outputs a file that is a clean input to the next tool in the chain.
How long does Favtoo retain my data after using Prime Number Generator?
Favtoo keeps no copy of your file because Favtoo never receives your file. Prime Number Generator 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.
Why did Prime Number Generator reject my input?
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 Prime Number Generator over a folder of files?
Prime Number Generator 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 fast is Prime Number Generator?
Most jobs finish in seconds. Speed scales with input size and with how many CPU cycles your browser tab has available — the engine runs in your browser, so it shares resources with whatever else you have open. For inputs near the 0 MB ceiling, expect anywhere from a few seconds to roughly a minute on a typical laptop. Closing other heavy tabs noticeably speeds things up.
Can I use Prime Number Generator on iOS or Android?
Prime Number Generator 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.