For centuries people have looked to the wisdom of Nostradamus in order to see into the future. In modern times few problems have vexed mankind more than when the McRib(tm) sandwich will be available. Now, thanks to the power of McRibadamus, they can know the fate of the value meal they love so much.
Christoph (@folkengine)
In this exercise you will create an application that attempts to predict the availability of the McRib based upon the price of Lean Hog Futures (Pork) traded on the Chicago Mercantile Exchange.
Lean Hog Futures trade for the months of February, April, May, June, July,
August, October, and December. Each month has a standard futures month code.
A contract symbol is built as HE + month code + two-digit year + .CME,
and Yahoo Finance's v8 chart API will return current market data for it as
JSON:
https://query1.finance.yahoo.com/v8/finance/chart/<SYMBOL>
| Month | Code | Example (next offering as of July 2026) |
|---|---|---|
| February | G | HEG27.CME |
| April | J | HEJ27.CME |
| May | K | HEK27.CME |
| June | M | HEM27.CME |
| July | N | HEN27.CME |
| August | Q | HEQ26.CME |
| October | V | HEV26.CME |
| December | Z | HEZ26.CME |
The continuous front-month contract is also available as
HE=F.
Notes on the endpoint:
- Prices are quoted in US cents per pound (the payload reports currency
USX). - The current price is buried in the response at
chart.result[0].meta.regularMarketPrice— digging it out of the surrounding noise is part of the exercise. - Send a browser-ish
User-Agentheader; some environments get a 429/403 without one. - This is Yahoo's unofficial-but-public API — the same one its own site uses. It has broken before (see A Word From History). Consider capturing real responses as local fixtures so your tests run offline and your kata outlives the endpoint.
This iteration covers the core functionality: computing which contracts to look at, grabbing the remote futures market data, and analyzing it to report on the likelihood that the McRib sandwich will be available during that period.
As a user I want to be able to retrieve the next markets for lean hog futures. At least nine markets should be computed. Since they are offered only on certain months, I will need to determine what the current month is and which markets are available.
- Determine the current month
- Determine which future markets will be available, rolling across year boundaries (nine offerings always spans at least two calendar years)
As a user I will want to know the Chicago Mercantile Exchange symbols for the lean hog futures that I am looking up, and the Yahoo Finance URLs that will provide the JSON data for those futures.
- Construct CME symbols (
HE+ month code + two-digit year +.CME) - Construct Yahoo Finance v8 chart URLs
As a user I want to take the latest futures data and report whether the McRib is likely to be available during each contract period.
- Retrieve and parse the JSON data, extracting the market price
- Compare the price to a threshold (default: 90.00 cents per pound)
- A price below the threshold means pork is cheap, and the McRib is likely; at or above it, unlikely
Why below? The McRib arbitrage theory holds that McDonald's brings back the McRib precisely when pork is cheap. (The 2015 kata had this backwards. Nostradamus nods knowingly.)
Example verdicts, using real prices captured 2026-07-19 with the default threshold of 90.00:
| Symbol | Price | McRib? |
|---|---|---|
| HEV26.CME | 87.95 | likely |
| HEZ26.CME | 78.775 | likely |
| HEG27.CME | 81.725 | likely |
| HEM27.CME | 97.5 | unlikely |
As a user I would like the McRibadamus predictions to be displayed on the web.
- Serve the engine's predictions as a JSON endpoint
- Serve a simple page that displays each upcoming contract and its verdict