Companion to the book
The Tool
Directory
Appendix A of Checkout Math names tools by what they do, not what they're called — because names change, and a printed book can't. This is the named list, and it lives here so it can stay current.
Everything below is a current example of a category described in the book. Tools get bought, get worse, and disappear — when one does, find its replacement under the same heading. Nothing here is an endorsement or a paid placement, and free tools that can see your browsing are noted as such. Last reviewed: July 2026.
A.2 — Price history & tracking
Price-history charts
What an item has actually cost over months, so a "sale" is checkable against a real prior price.
- CamelCamelCamel — price history for one large marketplace, free, web + extension
- Keepa — deeper history and drop alerts for the same marketplace; browser extension
- PayPal Honey / other coupon extensions — include history features; see the caveat below
Fare & hotel watches
A watch on a route or a room that emails you when the price moves, so you stop refreshing.
- Google Flights — price tracking and history on a route, free
- Hopper — fare and hotel watches with a rise/fall estimate (treat as a forecast)
- Kayak / Skyscanner price alerts — route watches, free
The extension caveat. A browser extension can see the pages you visit — that permission is what makes a price-history tool work. Some free ones are monetised through that visibility. Before you install: read the permissions it asks for, and check who owns it now. Extensions change hands, and the new owner inherits everything the old one could see. When a free tool's value is obvious but its revenue isn't, assume the browsing is the product, and decide if that trade is worth it for that tool.
A.3 — Comparison & all-in pricing
Unit price & groceries
Cents per ounce is the only honest comparison between two package sizes.
- Your phone's calculator — the unit-price tool you already have
- Store apps' own unit-price display — where offered, read it, don't trust the shelf number
Fuel
For a station you'd pass anyway — never a reason to drive out of your way.
- GasBuddy — current per-gallon prices near you, free
- Your map app — many now show fuel prices along a route
Broadband labels
Compare the ongoing price across providers, not the introductory one.
- Providers' own standardised broadband labels — required to be shown; read the after-promo price
- The regulator's consumer-broadband label pages — how to read a label side by side
Total price
For anything where the advertised price isn't the price.
- Carry every offer to the final checkout screen before comparing — the last number is the only comparable one
A.4 — Documentation & escalation
Capture
- Your phone's screenshot — price, date, URL, and cart state, taken before checkout
- An email folder or label for "purchases I might contest" — receipts gathered on the day, not hunted for later
Where a complaint goes
Reach for the most specific venue. Named current agencies:
- Deception / undisclosed fees → your state attorney general's consumer division
- Utilities (power, gas, water) → your state utility commission
- Airlines → the U.S. DOT aviation-consumer complaint process
- Phone / cable / internet → the FCC or your state utility commission
- Insurance → your state insurance department
- Credit / lending / payments → the federal financial-complaint venue (verify its current name and status)
A.5 — Legislative trackers
Find your state's bills
- Your state legislature's site — search surveillance pricing, algorithmic pricing, all-in pricing, junk fees
- LegiScan — the same search across all 50 states and Congress, free
- BillTrack50 / Open States — follow a specific bill and get emailed when its status changes
Comment while it's in committee
The one moment your input is structurally invited — and the rung nearly everyone skips. The bill's own page on your legislature's site says how to submit written comment or register a position.
A note on this page
Why the list lives here and not in the book
The book describes every tool by what it does, so it never goes stale. This page carries the volatile half — the current names — where it can be corrected the day a tool changes. If something here is dead or wrong, that's the page's fault, not the book's. Tell me: jan@janlukin.com.