Which file converters upload your files? (and how to check)

Why "upload" is about architecture, not trustworthiness

Whether a converter uploads your file is decided by how it is built, not by how reputable it is. There are two designs. A server-based converter sends your file to a remote machine, converts it there, and returns the result; this is how almost every online converter works, and it is a normal, legitimate model. An in-browser converter runs the conversion on your own device in WebAssembly, so the file never leaves your machine.

The distinction matters because the two named realities are different in kind. With a server-based tool you are trusting an operator's stated policy on handling, encryption, and deletion, which you usually cannot independently check. With an in-browser tool there is nothing to upload, so there is nothing to intercept, retain, breach, or subpoena, and you can confirm that with a test. Neither design is an accusation against the other. Server conversion is the right and often the only choice for jobs a browser genuinely cannot do, and the established server converters are real companies with published policies. The useful question is simply: for this particular file, do I want a promise I trust, or a fact I can verify?

Fair comparison of the major online converters (as of 2026)

All of the services below are legitimate, established, server-based converters. As of 2026 each uploads your file to convert it, and each has its own deletion policy. These are point-in-time facts worth re-checking on each company's own site, since any provider can change its terms.

CloudConvert (server-based, uploads your file): uses SSL/TLS in transit, converts in isolated containers, and deletes files after a short period. Free tier is around 25 conversion minutes per day. Pricing is either prepaid packages whose credits do not expire (for example roughly 500 minutes for about 8 dollars) or monthly subscriptions whose unused credits expire at month-end. Genuine strengths: broad format support, a mature API, and the isolated-container handling plus non-expiring package option are real advantages.

Convertio (server-based, uploads your file): deletes files after 24 hours. Genuine strength: broad format support.

Smallpdf (server-based, uploads your file): TLS in transit, deletes files after about one hour. Genuine strengths: a polished, PDF-focused user experience that many people find the smoothest for PDF tasks.

FreeConvert (server-based, uploads your file): purchased top-up credits expire 30 days after purchase. Genuine strengths: strong GPU-backed video and broad format support, which is excellent for heavy batch video.

Zamzar (server-based, uploads your file): free tier is 2 files per 24 hours; paid is a recurring subscription (around 25 dollars per month for Basic as of 2026). Genuine strengths: very broad format support and a long-established service.

None of these offer a verifiable no-upload mode, and none claim to; that is simply not what server conversion is. hushvert (in-browser for the conversions a browser can do): images including HEIC, audio, archives, and PDF page operations run on your device and never upload, which you can verify, and those conversions are unlimited and free with no account. Its server lane (office documents to PDF, PDF to Word, large video) does upload and is clearly labeled before you start. Honest trade-off: hushvert supports fewer total formats than the broad server converters and has no GPU video.

The one thing in-browser conversion adds: a result you can verify

Every converter on the list above is trustworthy enough that millions of people use it, and for most files that is the end of the matter. The single durable difference with in-browser conversion is not that it is more honest in intent; it is that the no-upload claim is checkable rather than promised.

For images (including HEIC), audio, archives, and PDF page operations, hushvert runs the conversion inside your browser, so the file is never uploaded, and you can prove it two ways: switch to airplane mode and watch it still convert, or open the Network tab and watch no request carry your file's bytes. A CI test runs on every code change and fails the build if any request during a client-side conversion carries file bytes, so the guarantee cannot quietly regress between releases. The conversion engine is open source under the MIT license, so you can read exactly what runs in your tab. That is the honest, durable differentiator, and it is the whole claim; we do not extend it beyond the conversions a browser can actually do.

How to check any converter yourself: the Network-tab test

You do not have to trust this page either. Here is how to see, with your own eyes, whether a converter uploads your file.

1. Open your browser's developer tools (press F12, or right-click the page and choose Inspect; on Mac, Option+Command+I). 2. Click the Network tab. Tick "Preserve log" so requests are not cleared. 3. Optionally clear the list, then select your file and run the conversion. 4. Watch the rows that appear during the conversion. You are looking for an outbound request (a POST or PUT) whose body is roughly the size of your file.

How to read it: a real upload is large and scales with your file. Convert a 4MB photo and an upload shows a request body near 4MB; convert a 200KB file and it is near 200KB. Page assets (scripts, styles, a one-time codec download) are downloads, not uploads, and an analytics ping is a tiny outbound request, usually under a couple of kilobytes, that does not grow when your file does. If you convert a 4MB file and nothing close to 4MB leaves your machine, your file was not uploaded. The full step-by-step version, including how to tell an analytics ping apart from a real upload, is on the how to verify a converter does not upload page.

The 10-second version: the airplane-mode test

If developer tools feel fiddly, there is an even simpler, more decisive test that needs no technical skill. The logic is airtight: a converter that uploads your file cannot work without a network. If it still converts with the network off, nothing was uploaded, because there was nowhere to send it.

1. Open the converter and let the page load fully (this step needs the network; an in-browser tool downloads its conversion engine once here). 2. Turn on airplane mode, switch off Wi-Fi, or unplug ethernet. Confirm you are actually offline by trying to load any other site. 3. Convert your file.

If the conversion finishes while you are offline, the work happened on your device and the file never left it. If the tool spins, errors, or refuses to start, it needs a server and is uploading your file. One honest caveat: do the first conversion online so any engine finishes downloading, then go offline and convert again to be sure. hushvert ships a live version of exactly this test on its privacy-proof page: it loads the codec, invites you to disconnect, converts a locally drawn image offline, and counts every network request the conversion makes, so the page cannot fake the result.

Which converter should you use? A fair recommendation

Match the tool to the file. For non-sensitive files, or for jobs that need a format or capability a browser cannot provide, the established server converters are excellent choices, and each has a real strength: CloudConvert for breadth, a mature API, isolated containers, and non-expiring packages; FreeConvert for fast GPU-backed batch video; Smallpdf for a polished PDF experience; Convertio and Zamzar for very broad format coverage. Picking one of these for a meme image or a throwaway document is a perfectly reasonable trade.

When the file is sensitive (an ID scan, a contract, medical paperwork, a personal photo) or you simply prefer not to upload, an in-browser converter removes the upload, and the trust question, entirely. That is where hushvert fits: its image (including HEIC), audio, archive, and PDF page operations run on your device, unlimited and free, and you can prove no file leaves your browser. For the conversions a browser cannot do, hushvert uses a clearly labeled server lane that uploads over an encrypted connection and deletes files (inputs immediately after conversion, outputs within about an hour). Many people use both: an in-browser tool for private and common conversions, and a broad server converter for the occasional heavy-video or exotic-format job. The point of this page is not to pick a winner for you; it is to make the upload question one you can answer yourself.

Keep reading

• How to verify a converter does not upload your file
• hushvert vs FreeConvert
• hushvert vs Zamzar
• See the no-upload proof
• File converter FAQ

Common questions

Do online file converters upload your files?

Essentially all mainstream online converters do, because they are server-based: your file is uploaded to their servers, converted there, and the result is sent back. As of 2026 that includes CloudConvert, Convertio, Smallpdf, FreeConvert, and Zamzar. This is normal and not an accusation. The exception is an in-browser converter, which runs the conversion on your own device so the file never uploads. You can confirm which kind you are using with the airplane-mode test or the browser Network tab.

Which file converters do not upload your files?

In-browser (client-side) converters do not upload, because the conversion runs in your browser. As of 2026, hushvert runs image (including HEIC), audio, archive, and PDF page conversions entirely on your device, and you can verify it in airplane mode or the Network tab; a CI test fails the build if a file byte ever leaves the browser. The mainstream server-based converters do not offer a verifiable no-upload mode. hushvert's own server lane (office docs to PDF, PDF to Word, large video) does upload and is clearly labeled before you start.

Is CloudConvert safe?

CloudConvert is a real, established, legitimate service. As of 2026 it is server-based, so it uploads your file; it uses SSL/TLS in transit, converts in isolated containers, and deletes files after a short period. Its prepaid package credits do not expire, which is a genuine advantage, and it has broad format support and a mature API. As with any server converter, you are trusting its stated handling and deletion policy rather than verifying it yourself, which is a reasonable trade for non-sensitive files. For a private file, an in-browser converter removes the upload entirely.

Is Smallpdf safe?

Smallpdf is a reputable, polished, PDF-focused service. As of 2026 it is server-based, so it uploads your file, uses TLS in transit, and deletes files after about one hour. Its user experience is a real strength. Like every server converter, it asks you to trust a policy you cannot independently check; that is fine for most documents. If a PDF is sensitive and you would rather not upload, an in-browser tool lets you do PDF page operations on your device and prove nothing was sent.

How do I check whether a converter uploads my file?

Two free tests. The airplane-mode test: load the converter fully while online, then turn on airplane mode and try to convert; if it still works offline, your file was not uploaded. The Network-tab test: open developer tools (F12), click the Network tab, run a conversion, and look for a large outbound request roughly the size of your file. A real upload scales with your file size; an analytics ping stays tiny. Both tests work on any converter, including hushvert.

Why does hushvert still upload some conversions?

A few conversions need software a browser cannot run: office documents to PDF, PDF to Word, and large video. Those use a clearly labeled server lane that uploads over an encrypted connection and deletes files (inputs immediately after conversion, outputs within about an hour). Every conversion a browser can do, including all HEIC conversions, stays on your device and never uploads. The dropzone tells you which lane a conversion uses before you start, so the upload is never a surprise.