People ask the same question before they drop a bank statement or a resume into an online tool: does this file leave the browser? The honest answer on ToolSink depends on the job. This page is the map we use ourselves, taken from the pages and the API that ship with the site.
Jobs that stay on your device
Calculators never see a file. EMI, SIP, fixed deposit, GST, BMI, and the other numeric tools read the numbers you type and run the formula in the page. The worked example under each of those calculators is the same arithmetic the widget uses. If the example and the widget disagree, the page is wrong and we should fix the page.
Create PDF is also local. The preview you see is a PDF built in the browser with the same document definition as the file you download. Text size, alignment, and the order of title, image, and body are part of that definition. There is no second layout applied at download time.
Rotate PDF, watermark PDF, remove pages, Word to PDF, HTML to PDF, and Add Images to PDF use pdf-lib or pdfmake in the tab. Resume export, image watermarking, and the text utilities (case, counters, compare, sorters) do the same. Closing the tab drops the input.
Jobs that upload for one request
Four PDF actions post the file to our API:
- Merge PDF sends every selected file to
POST /api/pdf/merge. - Split PDF sends one file to
POST /api/pdf/splitand returns a zip of pages. - Compress PDF sends one file to
POST /api/pdf/compress. - Image to PDF sends the images to
POST /api/pdf/images-to-pdf.
Merge is the clearest example of what “processing” means. The API opens each upload, copies the pages into a new PDF in the order you arranged, and returns merged.pdf. It does not reflow the text and it does not resize an A4 page to match a Letter page sitting next to it. Bookmarks from the originals are not rebuilt into the new file.
There is no user account, so the result is not stored in a library you can reopen later. The controller reads the upload streams, returns the bytes, and disposes those streams. A large upload may sit in a temporary buffer for the length of the request. That is not the same as keeping a copy you can download again tomorrow.
Encrypted PDFs are not stripped of their password on the way through. The reader opens the file for import. If it cannot, the request fails. The page should show that error rather than a partial merge that quietly skipped a file.
What we do not claim
“Runs in your browser” on the homepage describes the calculators, Create PDF, rotate, and the text and image tools that never call the PDF API. It does not describe merge, split, compress, or Image to PDF. Those four need the API process to be running. If it is not, Merge PDF says the merge failed because the backend is not running.
We also do not treat a formula page as financial or medical advice. The EMI figure is the reducing-balance formula with the rate and tenure you typed. It is not a lender’s schedule, and it ignores processing fees. BMI is weight divided by height squared, placed in the adult WHO bands. It is a screening label, not a diagnosis.
Why this page exists
A directory of similar widgets is easy to publish and hard to trust. The useful part of ToolSink is the job plus the method: which inputs the tool actually reads, whether the file is uploaded, and one numeric walkthrough you can check with a calculator. When a page cannot say those three things, we take it off the public directory instead of writing another generic paragraph under it.
If a tool on the site contradicts this note, use the contact page. The correction belongs in the tool guide and in the site updates log, not in a rewritten slogan.