Remworth Lens · browser extension · its own product · included with any subscription
An FBA calculator Chrome extension. Every extension can read the listing. This one reads your books.
On any amazon.com product page, Lens shows what every FBA calculator shows — profit, ROI, fees, rank, history. Then it shows what no standalone extension ever can: whether you've bought this exact ASIN before, how many units you have on hand right now, and what you really paid — your true FIFO cost, one click from being the buy cost in the calculator. A standalone extension can't copy that. It has no ledger to read. $9.99/mo standalone; included with any Remworth subscription.
7 days free · the full product on your real data · card required · cancel any time
- Public data
- profit, fees, rank, history — like the extension you run now
- Your data
- bought-before, on-hand, true FIFO cost — like nothing else
- History charts
- included, no second data subscription
- Parity
- the exact numbers you're used to, cell for cell
- Price
- $9.99/mo standalone · included with any plan
- Bill one
- the calculator extension
- Bill two
- the data subscription it needs for a price chart
- The blind spot
- your own purchase history — invisible to both
- The forgetting
- fifty costs typed on your phone, never on your laptop
- The rebuy
- 200 units of the ASIN you lost money on last winter
You're sourcing against your own memory.
Standing at a shelf, or fifty rows deep in a storefront: have I bought this before? What did I pay? Do I still have units at FBA? Your calculator extension can't tell you — it has no ledger to read. It charges you a second subscription for history charts on top. And it stores your buy costs and notes in the browser, warning you in its own words that they don't sync across devices. You're sourcing against your own memory, on rented data, in a tool that admits it forgets.
- Bought before
- yes/no, with lifetime units and last-sold date
- On hand
- your live units, right now, from your real inventory records
- True cost
- FIFO, identical to your P&L's figure
- One click
- historical cost → calculator buy cost
- Never touched
- stated plainly, not left blank
"Bought before: yes. On hand: 14. Your real cost: $6.42. Use it?"
While you're on the listing, Lens reads your actual Remworth ledger: bought-before or not, units on hand right now, true FIFO cost per unit — the same figure the rest of Remworth uses, so the widget and your P&L can never disagree — lifetime units sold, last-sold date. One click drops your real historical cost into the calculator: "Use $X.XX as buy cost." Never touched the ASIN? It says so, plainly. Every other number in a sourcing widget is public data any tool can fetch. This one comes from your accounting, and only ours has your accounting.
- Ranges
- 30 / 90 / 180 / 365 / 730 days
- Series
- eleven, toggleable
- Second bill
- none — served through Remworth
- Lookups
- included while you browse — no separate data bill
- Short history
- a product with only 30 days of data says so in the 90/180-day cells — never a misleadingly low count wearing the wrong label
Browse 300 products. Pay for zero data lookups.
Full price-and-rank history on every product, served through Remworth's own data service — no separate market-data subscription to buy, no key to babysit, no per-lookup charges while you hunt. The chart is embedded in the widget: 30 to 730 days, eleven toggleable series — Amazon price, 3rd-party new, FBA/FBM, Buy Box, used, sales rank, offer count, units sold, rating, review count — with an optional inverted rank axis if that's how you read rank. Is today's price real, or a spike somebody's about to tank? Two years of history answers it, and the answer stopped costing extra.
- Recalc
- every keystroke, no second tab
- Fee bands
- follow YOUR typed price, not the page's
- Max Buy Cost
- from your rules, not house defaults
- FBA/FBM
- one-click toggle swaps the whole fee model, your merchant shipping included
- Variations
- clicking a different size or color re-reads automatically — no stale child-ASIN numbers
Type a price. Watch every number move.
A profit widget under the title on any amazon.com product page: type a sell price and a buy cost, and net profit, ROI, and margin recalculate on every keystroke. Fee bands follow the sell price as you type — Amazon's fulfillment fee changes below $10, $10–50, and above $50, and the widget picks the right band live instead of locking to the page price. Price at $9.49 to undercut and you'll be charged the sub-$10 fee; your calculator should know that before you do. Breakeven price and Max Buy Cost compute against your own rules — minimum net dollars, ROI %, or margin % — because in the aisle, "the most I can pay" is the only number you act on. Side-by-side target tables show min sell price and max buy cost at each target you define ($0/$1/$2, or 0/10/15%): the supplier quotes three case prices, and you see at a glance which one is a deal and which is charity.
- Itemized
- referral, FBA, closing, placement, storage — each with its why
- Source
- maintained rate-card tables with recorded effective dates
- Per-ASIN
- referral rate from your own connection when available, source labeled
- Inbound
- your $/lb rate, separate hazmat rate, optional dimensional-weight mode
- The rule
- a missing fee shows a named reason on hover — never an optimistic guess or a friendly zero
Fees from Amazon's published rate card, with effective dates on file.
Referral fee with the $0.30 minimum, FBA fulfillment by size tier and price band, variable closing fee, inbound placement, monthly storage — itemized, with size tier, program, and season shown so you can see WHY the fee is what it is. The rate tables carry recorded effective dates and are maintained as tables, not scraped from help pages — so Lens doesn't break the week Amazon rewords a sentence. With a connected account, the referral rate for that exact ASIN comes straight from Amazon instead of a category table, and the data source is labeled either way. Cost realism is yours to set: buy-side tax, editable prep chips (bag, tape, label, bubble), storage months, catch-all per-unit costs, and a configurable ROI method — buy cost alone, plus other costs, or plus inbound — so ROI computes the way YOU compute it.
- Missing fee
- named reason on hover, never invented
- Missing cost
- no ROI shown — it would be fiction
- Rank drops
- 30/90/180 days, threshold mode optional
- Demand
- Amazon's own monthly figure — sourced, never estimated by us
- Amazon presence
- out-of-stock % over 30 and 90 days
A missing fee shows a named reason. Not an optimistic guess.
No dimensions on file? No buy cost entered? No fulfillment fee available? The cell shows a labeled gap with the reason on hover — never an invented ~$3 fee that turns a loser into a "winner" somebody buys forty units of. The demand stats hold to the same standard: current rank and category live from the page, rank drops over 30/90/180 days with an optional 3%-threshold mode so wobbles don't count as sales, average rank per window, Amazon's own "bought in past month" figure, and Amazon's out-of-stock percentage over 30 and 90 days. Demand data with a source, not a vibe.
- Gating source
- Amazon itself, asked on your own credentials — durable when Amazon rewords its pages
- Failure mode
- "unknown," said out loud
- Offers
- stock counts, win share, live-first sorting
- Price-band count
- offers within X% of low FBA — threshold yours
- Variations
- the one child that actually sells, spotted
The three questions between you and the buy, answered where you stand.
Gating: one click asks Amazon directly, on your own connected account — restricted or can-sell for YOUR account, Amazon's reason messages on hover, "unknown" reported honestly when the check can't complete. Never a false green. It runs on demand — only when you ask; without a connection the widget still works, and this one check names what's missing. A hazmat tier and battery flag with the underlying reason codes rides along. The verdict is the scope — the approval application is yours to file. Offers: one click opens every seller — FBA/FBM/Amazon badge, condition, price, stock count, Buy Box win share, feedback — live offers sorted first so a dead offer at a great price can't fake the floor; columns configurable; loads only when opened. A summary strip counts the offers within your set % of the low FBA price: the set you'd actually be pricing against. Variations: every child ASIN with its own rank, monthly sold, Buy Box price, low FBA, and offer count — up to 100 in one batched lookup, the current one highlighted, each linked. The parent looks great; only black/medium sells. See that before you buy the size run. No variations? It says so plainly.
- Surfaces
- search results + competitor storefronts
- Strip
- five numbers that decide the click
- Performance
- one batched call per page, infinite-scroll aware
- Toggle
- per surface, in settings
- The refusal
- no buy cost, no fake ROI — on purpose
Sixty tabs of storefront stalking, down to one scroll.
On Amazon search pages and seller storefronts, Lens paints a compact strip under every tile: rank, 30-day rank drops, monthly sold, FBA offer count, and combined referral + FBA fee at the tile's listed price. One batched call per page of results, keeps up with infinite scroll, toggleable per surface. And deliberately: no ROI on tiles. Without a buy cost, an ROI would be fiction — so we don't print one.
- Buy costs
- per ASIN, auto-saved, everywhere
- Notes
- your own text, synced — who you called, what the case price was
- Stars
- a 500-ASIN keep-for-later list
- Saving
- on blur, automatic
- Their confession
- "doesn't sync." Ours does.
Fifty buy costs typed on your phone at the wholesaler. All fifty on your laptop that night.
The buy cost you type, the note you jot, the star you tap — saved to your Remworth account, not the browser. Buy costs auto-save per ASIN and reload on any device. Notes sync. Star up to 500 keep-for-later ASINs. Everything saves on blur; there is no save button to forget. Competing extensions store this in the browser and warn you, in their own words, that it doesn't sync across devices.
- Table
- USPS Ground Advantage Commercial, zones 1–8, to 10 lb, effective date recorded
- Surcharges
- length and cubic-foot, automatic
- 2026 rule
- sub-pound pricing, in
- Alternatives
- $/lb or flat rate, your choice
- Beyond the table
- refused, by name
Postage from a real USPS rate table — and an honest refusal outside it.
Outbound postage estimated from a real USPS Ground Advantage Commercial rate table by weight and zone — zones 1–8, to 10 lb — with length and cubic-foot surcharges applied automatically and USPS's 2026 sub-pound pricing rule built in. A ship-revenue field for what the buyer pays you; simpler $/lb or flat-rate models if you prefer. Anything outside the table — zone 9, over 10 lb, Priority Mail — refuses by name rather than extrapolating a wrong number into your margin. Under one flat shipping guess, half an FBM seller's "profits" are fiction. Not here.
- Parity
- cell for cell with the extension you know
- Import
- one file, one click, every key mapped or explained
- Tested
- against a real competitor settings export
- Depth
- eight tabs, per marketplace, every assumption yours
- Backup
- named configurations, export/import
Same numbers. Same settings. Zero re-entry.
The calculator reproduces the output of the profit-calculator extension sellers already know, cell for cell — on day one you see the exact numbers you're used to, because unfamiliar math is the real reason switches fail. Then import the settings export from the extension you're leaving: every key is either mapped onto Lens or listed with the stated reason it doesn't apply — nothing silently dropped. The import is tested against a real settings export from the leading competitor. Underneath, eight settings tabs keyed per marketplace — FBA costs, Merchant, Pricing, Targets, Display, Variations, Links, Data — cover every assumption: inbound $/lb regular and hazmat, placement fees by region and split count, storage months, prep chips, buy-side tax, target lists, per-channel Max Buy Cost rules, widget position (9 spots), font size, stat rows, column sets, default sell-price source order — plus named configurations and settings export/import for a backup or a second machine.
- Clipboard
- tab-separated — pastes straight into a grid
- CSV
- 35 fields, your pick
- Withheld column
- blank ≠ bad, and the export says which
- Links
- fully custom, template variables, per marketplace
- Disabled links
- shown with the reason, never vanished
One keystroke, one spreadsheet row — with a Withheld column riding along.
Copy a tab-separated, paste-straight-into-a-grid row to the clipboard, or download a CSV with your exact pick of 35 fields — identifiers, rank stats, prices, every calculator output, fees, dimensions, offer counts. A "Withheld" column travels with every export, so a blank profit cell in your buy list is never mistaken for a bad product a week later. The honesty follows the data into your own spreadsheet. Custom research links round it out: one-click links to the shopping and price-history sites you cross-check, plus any link you define with template variables (TITLE, TITLE6, ASIN, UPC, ISBN10, ISBN13, MODEL), per marketplace — and a link that needs a fact this product lacks shows disabled with the reason, instead of silently vanishing.
- Sign-in
- zero-friction, via the web app in the same browser
- Logout
- automatic disconnect
- Permissions
- amazon.com + the Remworth app. That's all.
- Credentials
- your password never enters the extension
- Install
- a Chrome extension — not on the Web Store yet
No password ever touches the extension.
Sign in to the Remworth web app in the same browser and Lens connects itself — and disconnects on logout. Permissions are minimal: it runs only on amazon.com and the Remworth app, with no access to your other tabs or browsing. Your seller account is your livelihood; an extension that wants everything is a hard no, and we agree. Install is the normal kind: Lens is a Chrome extension. It is not on the Chrome Web Store yet. Once installed, it connects itself the moment you're signed in to Remworth in the same browser.
The bill math
Keep your numbers. Add your books.
Standalone: $9.99/month. With any Remworth subscription: included. A switcher typically drops two bills — the old calculator extension and the data subscription it needed for charts — for at most one.