[{"data":1,"prerenderedAt":633},["ShallowReactive",2],{"en-guide-privacy-online-tools":3},{"id":4,"title":5,"body":6,"description":618,"extension":619,"locale":620,"meta":621,"navigation":622,"path":623,"publishedAt":624,"seo":625,"showToolCatalog":622,"slug":626,"stem":627,"tags":628,"__hash__":632},"guide\u002Fguide\u002Fprivacy-online-tools-en.md","Online tools — is it OK to upload? The case for privacy-first browser-based processing",{"type":7,"value":8,"toc":583},"minimark",[9,38,41,46,53,56,63,66,80,83,89,91,95,98,110,113,116,121,124,128,131,135,142,146,153,155,159,166,183,190,193,204,207,211,217,223,229,235,241,245,248,254,260,266,268,272,275,279,282,293,296,307,311,318,323,363,373,376,380,387,390,392,396,403,407,410,454,458,465,476,478,482,485,487,491,495,498,502,505,509,512,516,523,527,534,538,541,543,547,554,557,569,575,580],[10,11,12,19],"blockquote",{},[13,14,15],"p",{},[16,17,18],"strong",{},"In this article",[20,21,22,26,29,32,35],"ul",{},[23,24,25],"li",{},"How mainstream online tools silently upload your files to servers",[23,27,28],{},"The privacy risks of server-upload tools",[23,30,31],{},"How browser-only tools work, and how to recognize them",[23,33,34],{},"The \"Zero send\" design principle behind Zerosend",[23,36,37],{},"How to verify for yourself that nothing is uploaded",[39,40],"hr",{},[42,43,45],"h2",{"id":44},"did-you-realize-your-files-were-being-uploaded","Did you realize your files were being uploaded?",[13,47,48,49,52],{},"You want to compress an image, merge PDFs, or convert an iPhone HEIC photo to JPG. Most people search for something like \"image compress online\" or \"PDF merge free\", land on a well-known site, and ",[16,50,51],{},"drag & drop the file",".",[13,54,55],{},"A few seconds later, the download button appears. Convenient, free, no install needed. It is a great experience.",[13,57,58,59,62],{},"There is just one thing: in those few seconds, ",[16,60,61],{},"your file left your computer",". Most online tools work by uploading the file to a server, processing it there, and sending the result back. For many use cases that is fine. For others, it is a real problem.",[13,64,65],{},"Examples where it matters:",[20,67,68,71,74,77],{},[23,69,70],{},"An employee merging internal contract PDFs",[23,72,73],{},"A journalist compressing portrait photos from an interview",[23,75,76],{},"A designer converting a client's logo PNG to WebP under NDA",[23,78,79],{},"A regular user resizing iPhone photos (with embedded GPS location) before sharing with anyone outside the family",[13,81,82],{},"In each case, files travel to a server somewhere — often in a different country, subject to different laws, kept for an unknown amount of time, and possibly accessible to staff or backups you cannot see.",[13,84,85,86,52],{},"This article explains why \"online tools\" tend to upload, and then introduces ",[16,87,88],{},"the other option: processing files without ever uploading them",[39,90],{},[42,92,94],{"id":93},"why-most-online-tools-upload-files","Why most online tools upload files",[13,96,97],{},"Most online tools trace back to the 2000s–2010s. Browsers at the time were simple display devices — they could not process complex images or video. So the standard design was:",[99,100,101,104,107],"ol",{},[23,102,103],{},"The browser uploads the file to the server",[23,105,106],{},"The server processes it (with ImageMagick, FFmpeg, and similar)",[23,108,109],{},"The server sends the result back for download",[13,111,112],{},"This has benefits for the operator: a powerful server gives consistent performance regardless of the user's computer, processing logs can inform product decisions, and in some cases user data can even be harvested as training material.",[13,114,115],{},"From the user's side, however, there are real risks:",[117,118,120],"h3",{"id":119},"risk-1-your-file-sits-on-someone-elses-infrastructure","Risk 1: Your file sits on someone else's infrastructure",[13,122,123],{},"Uploaded files are retained per the operator's terms of service. Many services state \"deleted after N hours\" but there is no way for the user to verify this. Backup handling, internal staff access, and subcontractor access are usually not disclosed.",[117,125,127],{"id":126},"risk-2-the-transit-path","Risk 2: The transit path",[13,129,130],{},"HTTPS protects the data in transit, but corporate proxies, school firewalls, and ISPs all see that a file is flowing to that domain. For anything covered by a strict corporate policy, that alone can be a violation.",[117,132,134],{"id":133},"risk-3-jurisdiction","Risk 3: Jurisdiction",[13,136,137,138,141],{},"Most large online tools are run by companies based in Europe or the US. The physical server location determines which ",[16,139,140],{},"government disclosure orders"," apply. GDPR (EU) and the US CLOUD Act have different privacy baselines, and for a Japanese user neither is under your control.",[117,143,145],{"id":144},"risk-4-exif-metadata-with-gps-coordinates","Risk 4: EXIF metadata with GPS coordinates",[13,147,148,149,152],{},"Smartphone photos carry EXIF metadata including ",[16,150,151],{},"GPS coordinates, timestamps, and camera model",". Drop one into an \"image compress\" site without thinking and you have just handed the operator your home's latitude and longitude.",[39,154],{},[42,156,158],{"id":157},"the-other-option-browser-only-tools","The other option: browser-only tools",[13,160,161,162,165],{},"Throughout the 2020s browsers have become dramatically more capable. Modern browsers can execute the following ",[16,163,164],{},"without any server involvement",":",[20,167,168,171,174,177,180],{},[23,169,170],{},"Resizing, compressing, and converting images that are hundreds of MB",[23,172,173],{},"Merging, splitting, and compressing PDFs",[23,175,176],{},"Trimming and converting videos (via FFmpeg compiled to WebAssembly)",[23,178,179],{},"Generating and reading QR codes",[23,181,182],{},"OCR on images",[13,184,185,186,189],{},"All of this runs inside JavaScript and WebAssembly on ",[16,187,188],{},"your device",". The file never leaves.",[13,191,192],{},"The flow looks like this:",[99,194,195,198,201],{},[23,196,197],{},"The browser reads the file into memory (no server upload)",[23,199,200],{},"Browser JavaScript processes it",[23,202,203],{},"The browser hands the result back to you as a download (also in memory)",[13,205,206],{},"The web server that hosts the site delivered HTML and JavaScript once. It never saw the contents of your file.",[117,208,210],{"id":209},"benefits-of-in-browser-processing","Benefits of in-browser processing",[13,212,213,216],{},[16,214,215],{},"1. Safe for confidential files","\nWork documents, client assets, medical-adjacent files, contracts — anything you would rather not push to a third party.",[13,218,219,222],{},[16,220,221],{},"2. No bandwidth for upload\u002Fdownload","\nConverting a large video used to mean hundreds of MB of round trips. In-browser processing reuses the bytes already on your device.",[13,224,225,228],{},[16,226,227],{},"3. Often faster","\nThe bottleneck is your CPU, not a network round trip. Small files feel instant and even big files often beat the upload route.",[13,230,231,234],{},[16,232,233],{},"4. Works offline","\nSites that ship as Progressive Web Apps can run offline after the first visit.",[13,236,237,240],{},[16,238,239],{},"5. You do not have to trust the operator","\nNo matter how the privacy policy is worded, the tool is technically incapable of uploading your file. That is a different category of assurance.",[117,242,244],{"id":243},"honest-trade-offs","Honest trade-offs",[13,246,247],{},"No approach is perfect. Browser-only tools have real weaknesses:",[13,249,250,253],{},[16,251,252],{},"1. Old browsers may not work","\nInternet Explorer and very old Android browsers are out. In 2026 this affects a small minority but still exists.",[13,255,256,259],{},[16,257,258],{},"2. Memory pressure on huge files","\nProcessing a 2GB+ video on a phone may run out of memory. Desktops are usually fine. Most tools publish their supported file size so you can check.",[13,261,262,265],{},[16,263,264],{},"3. Speed depends on your machine","\nServer tools have predictable speed on modern hardware. Browser tools run where you are. Old machines take longer.",[39,267],{},[42,269,271],{"id":270},"how-to-tell-is-this-tool-uploading-or-not","How to tell: is this tool uploading or not?",[13,273,274],{},"You can verify this yourself in a few minutes.",[117,276,278],{"id":277},"method-1-read-the-privacy-policy","Method 1: Read the privacy policy",[13,280,281],{},"Upload-based tools usually mention phrases like:",[20,283,284,287,290],{},[23,285,286],{},"\"Uploaded files are automatically deleted after N hours\"",[23,288,289],{},"\"Processing happens on our servers\"",[23,291,292],{},"\"Files are stored in AWS encrypted storage\"",[13,294,295],{},"In-browser tools typically say:",[20,297,298,301,304],{},[23,299,300],{},"\"Files are processed in your browser and not sent to our servers\"",[23,302,303],{},"\"Client-side processing\"",[23,305,306],{},"\"Files stay in your browser\"",[117,308,310],{"id":309},"method-2-check-devtools-definitive","Method 2: Check DevTools (definitive)",[13,312,313,314,317],{},"The most reliable check is your browser's ",[16,315,316],{},"DevTools",". You do not need to be a developer.",[13,319,320],{},[16,321,322],{},"Chrome or Edge",[99,324,325,328,336,343,346,349,356],{},[23,326,327],{},"Open the tool's page",[23,329,330,331,335],{},"Press ",[332,333,334],"code",{},"F12"," (DevTools opens)",[23,337,338,339,342],{},"Click the ",[16,340,341],{},"Network"," tab",[23,344,345],{},"Confirm the red record dot is on (network is being recorded)",[23,347,348],{},"Reload the page once so existing traffic shows up",[23,350,351,352,355],{},"Then ",[16,353,354],{},"drag & drop your file"," into the tool and run it",[23,357,358,359,362],{},"Watch the Network tab: does a ",[16,360,361],{},"new, large request"," (roughly the size of your file) appear?",[13,364,365,366,369,370,52],{},"If processing causes an upload of roughly the size of your file, it is a ",[16,367,368],{},"server tool",". If no such request appears, it is ",[16,371,372],{},"in-browser",[13,374,375],{},"Example: compressing a 5MB image in a server tool shows roughly a 5MB request in the Size column. In a browser tool, no such request exists.",[117,377,379],{"id":378},"method-3-try-offline","Method 3: Try offline",[13,381,382,383,386],{},"The ultimate test: ",[16,384,385],{},"turn off Wi-Fi"," (or unplug the cable) with the tool page already loaded, then process a file.",[13,388,389],{},"If processing works offline, it is 100% in-browser. If the tool requires a server, it fails when offline.",[39,391],{},[42,393,395],{"id":394},"the-zero-send-principle-behind-zerosend","The \"Zero send\" principle behind Zerosend",[13,397,398,399,402],{},"Our site, ",[16,400,401],{},"Zerosend",", takes the browser-only approach to the extreme. The name literally means \"zero send — nothing leaves your device\".",[117,404,406],{"id":405},"how-it-works-technically","How it works technically",[13,408,409],{},"Every Zerosend tool follows the same rules:",[99,411,412,430,436],{},[23,413,414,417,418,421,422,425,426,429],{},[16,415,416],{},"No file-sending code exists"," — no ",[332,419,420],{},"multipart\u002Fform-data",", no ",[332,423,424],{},"XMLHttpRequest"," or ",[332,427,428],{},"fetch()"," POST of file contents. These paths are simply not in the source.",[23,431,432,435],{},[16,433,434],{},"Content Security Policy restricts traffic"," — outbound connections are technically blocked except for analytics (Google Analytics) and ads (AdSense). A bug could not cause a leak because the browser would refuse the connection.",[23,437,438,441,442,445,446,449,450,453],{},[16,439,440],{},"All processing libraries are client-side"," — ",[332,443,444],{},"browser-image-compression"," for images, ",[332,447,448],{},"pdf-lib"," for PDFs, ",[332,451,452],{},"qrcode"," for QR codes, and so on. Everything runs in the browser.",[117,455,457],{"id":456},"transparency-commitments","Transparency commitments",[13,459,460,461,464],{},"\"Privacy-first\" is a marketing phrase many sites use. We try to treat it as a ",[16,462,463],{},"technical fact"," instead:",[20,466,467,470,473],{},[23,468,469],{},"The privacy policy documents the technical basis",[23,471,472],{},"A \"how it works\" page explains the implementation",[23,474,475],{},"Partial source code disclosure is on the roadmap",[39,477],{},[42,479,481],{"id":480},"zerosends-available-tools","Zerosend's available tools",[13,483,484],{},"Here are the tools available on Zerosend today. All of them run entirely in your browser and never send your files to a server.",[39,486],{},[42,488,490],{"id":489},"faq","FAQ",[117,492,494],{"id":493},"q-are-my-files-really-not-uploaded","Q. Are my files really not uploaded?",[13,496,497],{},"A. Yes, and \"Method 2\" above is the definitive way to confirm. With the Network tab open during processing you will not see a large request, because the file never leaves the browser.",[117,499,501],{"id":500},"q-why-do-so-many-sites-use-server-processing-instead","Q. Why do so many sites use server processing instead?",[13,503,504],{},"A. Legacy reasons (older browsers could not do this), operator benefits (logs, data collection), infrastructure migration cost, and in some cases intentional design to extend the time users see ads.",[117,506,508],{"id":507},"q-how-does-zerosend-make-money-with-browser-only-processing","Q. How does Zerosend make money with browser-only processing?",[13,510,511],{},"A. Ad revenue, same as many free tools. The ads are generic banner ads, unrelated to the contents of your files. We do not analyze your files for targeting.",[117,513,515],{"id":514},"q-can-i-use-this-for-corporate-confidential-files","Q. Can I use this for corporate confidential files?",[13,517,518,519,522],{},"A. Technically the data never leaves your device, so the usual upload concern does not apply. ",[16,520,521],{},"Your company's IT policy may still restrict use of any external website, though",", so please check with your IT \u002F security team before routing confidential work through any outside site — us included.",[117,524,526],{"id":525},"q-does-it-work-on-phones","Q. Does it work on phones?",[13,528,529,530,533],{},"A. Many tools do, but ",[16,531,532],{},"for large files a desktop browser is recommended",". Mobile browsers have memory limits and can fail mid-process on very big videos. Each tool page lists its recommended environment.",[117,535,537],{"id":536},"q-i-worry-about-gps-data-in-exif","Q. I worry about GPS data in EXIF",[13,539,540],{},"A. Zerosend tools keep EXIF by default today, but a dedicated \"EXIF strip\" tool is on the roadmap. Meanwhile, if location metadata worries you, strip it in your OS photo app or a local image editor before sharing.",[39,542],{},[42,544,546],{"id":545},"wrap-up-at-minimum-verify-once","Wrap-up: at minimum, verify once",[13,548,549,550,553],{},"If you already use online tools daily, ",[16,551,552],{},"the next time you use one",", open DevTools and watch the Network tab as you process a file. You will get a concrete sense of which tools upload and which do not.",[13,555,556],{},"From there, it is a matter of picking the right tool for the content:",[20,558,559,562],{},[23,560,561],{},"Harmless images (scenery you took yourself): any tool is fine",[23,563,564,565,568],{},"Sensitive files (internal docs, people's photos, contracts): pick a ",[16,566,567],{},"browser-only"," tool",[13,570,571,572,52],{},"Zerosend is designed for the second bucket. We aim to match the functionality of mainstream tools while holding the line on one promise: ",[16,573,574],{},"your files do not leave your browser",[13,576,577],{},[16,578,579],{},"No upload.",[13,581,582],{},"That is our commitment.",{"title":584,"searchDepth":585,"depth":585,"links":586},"",2,[587,588,595,599,604,608,609,617],{"id":44,"depth":585,"text":45},{"id":93,"depth":585,"text":94,"children":589},[590,592,593,594],{"id":119,"depth":591,"text":120},3,{"id":126,"depth":591,"text":127},{"id":133,"depth":591,"text":134},{"id":144,"depth":591,"text":145},{"id":157,"depth":585,"text":158,"children":596},[597,598],{"id":209,"depth":591,"text":210},{"id":243,"depth":591,"text":244},{"id":270,"depth":585,"text":271,"children":600},[601,602,603],{"id":277,"depth":591,"text":278},{"id":309,"depth":591,"text":310},{"id":378,"depth":591,"text":379},{"id":394,"depth":585,"text":395,"children":605},[606,607],{"id":405,"depth":591,"text":406},{"id":456,"depth":591,"text":457},{"id":480,"depth":585,"text":481},{"id":489,"depth":585,"text":490,"children":610},[611,612,613,614,615,616],{"id":493,"depth":591,"text":494},{"id":500,"depth":591,"text":501},{"id":507,"depth":591,"text":508},{"id":514,"depth":591,"text":515},{"id":525,"depth":591,"text":526},{"id":536,"depth":591,"text":537},{"id":545,"depth":585,"text":546},"How typical online tools upload your files to a server, how to tell them apart from tools that process entirely in the browser, and how you can verify this yourself with DevTools.","md","en",{},true,"\u002Fguide\u002Fprivacy-online-tools-en","2026-04",{"title":5,"description":618},"privacy-online-tools","guide\u002Fprivacy-online-tools-en",[629,630,631],"privacy","browser-local","pillar","hEBIya6hG4gEBjeDwGGIdyDZIsFQ2vvYLEPQy_UaVOg",1776723676903]