Privacy policy
Effective 18 August 2026 · applies to the MurmMargin browser extension, published by MurmTools.
MurmMargin sends nothing about you or the pages you read. It stores one thing — the price a listing declared, so it can tell you when a supplier moves it — and that stays on your device. It has no server of its own, no analytics and no tracking; its only network destination is ExtensionPay, which handles the paid tier. This page explains exactly how each of those is true rather than asking you to take it on trust.
What the extension does
When you click the MurmMargin icon on a supplier listing, it reads the prices that page declares in its machine layer — structured data, price metas — and gives you a live calculator: landed cost built the way customs charges it, your margin at the sell price you type, and the ad spend you can afford per sale before the unit loses money. Everything you type stays in the panel and is gone when it closes. If you have seen the listing before, it also tells you what the declared price did since.
What it stores, and where
MurmMargin remembers one thing, because the finding it exists for — a supplier quietly raising the unit price between your visits — is invisible unless you compare one visit to the next.
| Stored | Why |
|---|---|
| The listing’s host and path | To find the record again next time you open that listing. |
| The cheapest declared price, and its currency | So the next visit can say whether the supplier moved it. |
| A timestamp | Because “up 12% since 14 days ago” needs to know when you looked. |
The one thing that leaves your machine
MurmMargin has a paid tier, and paid tiers need a payment processor. Licence status and
checkout are handled by ExtensionPay, which is the only host the extension can reach —
https://extensionpay.com/* is the single entry in its permissions, so no other origin
is reachable even in principle.
What that traffic does not carry: the page you are reading, the prices it found, the sell price you typed, the suppliers you saved, or anything about the sites you visit. Those never leave your device. What ExtensionPay sees is what a payment processor must see — your payment email and whether your licence is current.
The panel's own footer says this, in the product, on every read: “Reads only this page, on your machine. The one thing sent anywhere is a licence check to extensionpay.com.” A build script fails the release if that sentence and the extension's permissions ever disagree — in either direction.
That is the whole record. No page text, no prices, no URLs beyond host and path, no identifiers
of any kind. It lives in chrome.storage.local — your browser, your device —
capped at three hundred listings, with the oldest dropped when the cap is reached.
None of it is ever transmitted. The extension has exactly one network destination —
the licence check described below — and this record is not part of it.
To erase it, remove the extension. Everything it stored goes with it.
The reading itself makes no network requests at all. It reads the page that is already open and writes to storage on your own device. The extension’s one piece of network traffic is the licence check described below, which carries nothing about the page or about you beyond what a payment processor must know.
Permissions
| Permission | Why it exists |
|---|---|
activeTab |
Grants temporary access to the single tab you clicked the icon on, and only at that moment. It is used to read the figures already published on that page. The access ends with the tab. |
scripting |
Runs one read-only function, once, in that tab. The function is bundled in the extension. It reads the page's structured data — JSON-LD offers and price metas — once. It does not modify the page, attaches no listeners, and does not persist after returning its result. |
storage |
Remembers one previous reading per page, so this visit can be compared with the last. The exact contents are listed above. Local to your device, capped at two hundred pages. |
There are no host permissions. MurmMargin has no access to any website until you click its icon on that website. It cannot run in the background, and it never touches another tab.
Data we collect
None. Collection means transferring data off your device. MurmMargin has no code path
that sends anything anywhere: no fetch, no XMLHttpRequest, no
WebSocket, no sendBeacon. The only URL in the package is a link to
murmtools.com in the panel footer, which does nothing until you click it.
Data we store
None. There is no storage permission, so the reading exists only while
the popup is open and is gone when you close it. Open the same page twice and it is read from
scratch both times.
Third parties
There are none. No analytics, no error reporting, no A/B testing, no advertising, no payment processor — MurmMargin is free and has no paid tier.
Even the typefaces are bundled inside the extension rather than fetched from a font host. A tool that reports what a page loads should not quietly load something itself.
What MurmMargin will not tell you
It does not tell you whether the product will sell. That is not on the page and not computable, so the panel prints an em-dash and the reason. Duty is applied as a band for the category the page itself declares — both edges printed — because the true rate is set by a tariff classification no browser extension performs. Every assumption the figures rest on is written next to them at the same size. And the price comparison never crosses a currency switch: inventing an exchange rate would manufacture a price change out of thin air.
Children
MurmMargin is a publishing and development tool. It is not directed at children and collects no data from anyone, of any age.
Changes
If this policy ever changes, the effective date above changes with it. Since the extension collects nothing, any change would be a narrowing rather than a broadening — and if that ever stopped being true, it would be stated here before it shipped.
Contact
Questions about this policy: [email protected].