Privacy Policy

STL Diff Online is built around a simple promise: your STL files never leave your browser. The diff itself runs entirely in JavaScript and a Web Worker on your machine. We never receive your geometry, your filenames, or any contents of your models.

What we don't collect

• STL file contents (parsed and diffed locally in your browser).
• STL filenames.
• Your IP address (beyond transient use for spam protection — see below).
• Your name, billing info, or any account data — there is no account.
• Cookies for tracking, advertising, or third-party analytics.

What we do collect

To understand whether the tool is useful and to keep it running, we record a small amount of anonymous, non-identifying telemetry:

• Anonymous session id — a random UUID generated in your browser and stored in localStorage. It lets us tell "one person did five diffs" from "five people each did one" without knowing who you are. Clearing your browser storage resets it.
• Diff event size — when a comparison completes, we log the byte sizes of the two files (not the contents, not the filenames) and a timestamp.
• Optional satisfaction rating — if you rate a comparison via the popover, we save the 1–5 star value, the optional pre-defined complaint reasons, and your optional "Tell us more" free-text note.
• Feedback messages — anything you type into the /feedback form on this site. If you provided an email, it is stored alongside the message so we can reply.
• Premium waitlist — if you submit your email on the Premium page, we store just that address.

Spam protection

Public form endpoints (feedback, premium signup) are rate-limited per IP address. The IP is used in-memory at request time and is not written to the database alongside your submission.

How long we keep things

• Anonymous diff events: kept indefinitely in aggregate form.
• Feedback messages with an email attached: kept until we reply, or for at most 90 days, whichever comes first.
• Anonymous feedback (no email): kept indefinitely as product feedback.
• Premium waitlist emails: kept until Premium launches and we send the launch email, then deleted.

Third parties

We do not share, sell, or rent any of the data described above with any third party. The application is hosted on Replit's infrastructure — they see standard request-level metadata (timestamps, IPs, response codes) the same way any web host would, governed by their own privacy policy.

Your choices

• To reset your anonymous session id, clear this site's localStorage in your browser settings.
• To remove a feedback message or waitlist email you previously sent, write to us via the feedback form and we'll delete it.

Changes

If we ever change what we collect, we'll update the "Last updated" date at the top of this page and call out the change in the footer's version badge.