Catching fake Black Friday discounts with a 400‑line browser extension (and the EU's 30‑day rule)

Description and use

The truediscount extension automatically verifies EU‑compliant 30‑day price rules on product pages, flagging inflated discounts and providing a privacy‑preserving badge.

Problem

Shoppers cannot easily verify if a displayed discount complies with the EU Omnibus Directive that requires the crossed‑out price to be the lowest price charged in the previous 30 days.

Outcome

truediscount provides instant, privacy‑preserving verification of EU‑compliant discounts, reducing consumer deception during Black Friday sales.

Workflow

• 1. User installs truediscount extension for Chrome or Firefox.
• 2. On a product page, the extension reads the crossed‑out price and the 30‑day low label (if present).
• 3. It parses European price formats, extracts the lowest price from schema.org JSON‑LD, Open Graph, microdata, or heuristics.
• 4. It compares the crossed‑out price to the 30‑day low and classifies the discount as real, inflated, or cheaper recently.
• 5. The extension displays a badge and optional price graph in a closed Shadow DOM.
• 6. If the extension misses a 30‑day label, the user can click "Report a problem" to open a prefilled GitHub issue for future fixes.

Evidence

Since 2022, the Omnibus Directive (2019/2161) says the crossed‑out "old price" of a sale must be the lowest price the shop charged in the previous 30 days.

Source

Everything stays in storage.local. No account, no analytics, no network requests.

Source

When your own browser has seen a lower price, that wins.

Source