Verifying Offline Processing in DevTools

Why verification matters

Many online tools claim to be "secure" or "private," but these terms can be vague or misleading. A tool might encrypt files during upload, delete them after processing, or store them in a "secure" data centre—but all of these still involve sending your files to external servers.

True offline processing is different: your files never leave your device. The good news is that you can verify this yourself using your browser's built-in developer tools. No technical expertise is required.

Step 1: Open developer tools

Every modern browser includes developer tools. Here is how to open them:

Alternatively, right-click anywhere on the page and select "Inspect" or "Inspect Element."

Step 2: Go to the Network tab

Once developer tools are open, click the "Network" tab. This shows all network requests made by the page—every file download, API call, and data upload.

Before testing, click the "Clear" button (usually a circle with a line through it) to remove any previous requests. This makes it easier to see new activity.

Step 3: Process a file

With the Network tab open and cleared, use the PDF tool normally. Select your files, perform the operation (merge, split, etc.), and download the result.

Watch the Network tab as you do this. You may see some requests—these are normal for any web application. What matters is whether any of them contain your file data.

Step 4: Analyse the requests

Click on each request in the list to see details. Look at:

• Request URL — Where is the request being sent? Legitimate requests go to the same domain (e.g., plain.tools). Suspicious requests go to external services.
• Request method — POST requests can carry file data. GET requests typically do not.
• Request size — Large requests (similar in size to your PDF) might contain file data. Small requests are usually just API calls or analytics.
• Request payload — Click on a request and look at the "Payload" or "Request" tab. Does it contain your file contents or references to your file?

What you should see with local processing

With a genuine offline tool like Plain, you should observe:

• No POST requests containing file data
• No requests to external file-processing services
• No requests with sizes matching your PDF files
• Only small requests for page assets, fonts, or minimal analytics (if any)

The processing happens in your browser's memory, invisible to the Network tab because it does not involve network activity.

Additional test: Go offline

An even simpler test: disconnect from the internet after loading the page, then try to process a file.

1. 1Load the PDF tool page while connected to the internet
2. 2Disconnect from Wi-Fi or unplug your ethernet cable
3. 3Select files and process them
4. 4If the tool works, processing is genuinely local

Server-dependent tools will fail or hang when offline. True client-side tools continue working because they do not need a network connection for processing.

What upload-based tools look like

For comparison, here is what you would see with a traditional online tool:

• A POST request to an upload endpoint (often with "upload" or "api" in the URL)
• Request size roughly matching your file size
• Content-Type header indicating file upload (e.g., "multipart/form-data")
• A subsequent download request for the processed file
• Tool fails to work when offline

This is not necessarily bad—many legitimate services work this way. But it does mean your files are being sent to external servers, which has different privacy implications than local processing.