Tesco Ireland vs Tesco GB: comparing grocery prices with two catalog API calls

This compares prices between Tesco Ireland and Tesco Great Britain by pulling both supermarket catalogs via Pepesto's /catalog endpoint. The script matches products by food category and shows which market is cheaper — reporting figures in both EUR and GBP.

$ PEPESTO_API_KEY=your_key node tesco-ie-vs-gb-price-gap.js

Getting started

If you have already checked out the GitHub repository:

export PEPESTO_API_KEY=your_key_here
node tesco-ie-vs-gb-price-gap.js

The first call — fetching both catalogs in parallel

The /catalog endpoint returns a full snapshot of a supermarket's product catalog, with prices, quantities, and entity names that are consistent across markets. Running both requests in parallel cuts the wait time in half.

async function fetchCatalog(domain) {
  const res = await fetch('https://s.pepesto.com/api/catalog', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'Authorization': `Bearer ${process.env.PEPESTO_API_KEY}`,
    },
    body: JSON.stringify({ supermarket_domain: domain }),
  });
  const data = await res.json();
  return data.parsed_products;
}

// Fetch both in parallel
const [ieProducts, gbProducts] = await Promise.all([
  fetchCatalog('tesco.ie'),
  fetchCatalog('tesco.com'),
]);

Each catalog entry has an entity_name — a normalised product category. Matching on entity_name lets me compare equivalent products even when the brand names differ:

{
  "parsed_products": {
    "https://www.tesco.ie/groceries/en-IE/products/250000335": {
      "entity_name": "Milk",
      "names": { "en": "Avonmore Milk 500Ml" },
      "price": 85,
      "currency": "EUR",
      "price_per_meausure_unit": "1.70 EUR / litre",
      "quantity_str": "500ml"
    },
    "https://www.tesco.ie/groceries/en-IE/products/250004694": {
      "entity_name": "Milk",
      "names": { "en": "Avonmore Milk 2 Litre" },
      "price": 269,
      "currency": "EUR",
      "quantity_str": "2l"
    },
    "https://www.tesco.ie/groceries/en-IE/products/250006087": {
      "entity_name": "Whipped cream",
      "names": { "en": "Avonmore Whipped Cream" },
      "price": 279,
      "currency": "EUR",
      "price_per_meausure_unit": "7.97 EUR / litre",
      "quantity_str": "350ml"
    }
  }
}

{
  "parsed_products": {
    "https://www.tesco.com/groceries/en-GB/products/250065690": {
      "entity_name": "Mozzarella cheese",
      "names": { "en": "Galbani Maxi Italian Mozzarella Cheese 250g" },
      "price": 295,
      "currency": "GBP",
      "quantity_str": "250g"
    },
    "https://www.tesco.com/groceries/en-GB/products/250167878": {
      "entity_name": "Ketchup",
      "names": { "en": "Heinz Top Down Squeezy Tomato Ketchup Sauce" },
      "price": 300,
      "price_per_meausure_unit": "0.65 / 100g",
      "quantity_str": "460g"
    },
    "https://www.tesco.com/groceries/en-GB/products/250044899": {
      "entity_name": "Honey",
      "names": { "en": "Tesco Organic Set Honey 340g" },
      "price": 335,
      "price_per_meausure_unit": "£0.98/100g",
      "quantity_str": "340g"
    }
  }
}

What the data showed

143 shared product categories matched across the two catalogs (simple matching against the product names). EUR/GBP have been close to parity, so the cent/pence prices are directly comparable for this exercise.

The pattern was clear: dairy is consistently cheaper in Ireland — Avonmore Milk 2 Litre at €2.69 in IE vs the closest Tesco GB equivalent at £2.89. For fresh produce, GB came out ahead. The biggest gap was in branded condiments: Heinz Ketchup 460g runs 300p in GB, €3.49 in IE. Tesco Organic Set Honey 340g showed a 40p gap in GB's favour. Galbani Maxi Italian Mozzarella Cheese 250g was nearly identical (£2.95 GB vs €3.25 IE) — effectively parity.

Next steps

A single snapshot only tells part of the story. Run this weekly for three months and chart the price drift. Promotional pricing skews results — the tesco.ie catalog had 23 items with promo_deadline_yyyy_mm_dd set, meaning those prices are temporary. Filtering those out gives a better like-for-like baseline.

The result

Two catalog API calls, 143 matched categories, and a category-level scorecard. Dairy cheaper in Ireland, branded goods cheaper in GB — the overall difference depends on your basket. Normalise by price_per_meausure_unit to eliminate pack-size distortion in the comparison.

What else you could do?

Extend to Lidl IE vs Lidl GB, where own-brand dominance makes the comparison cleaner. Add a normalisation step that converts everything to price-per-100g or price-per-litre before comparing, eliminating pack size distortion. Run the diff weekly and email items where the price gap changed by more than 10% — "these 5 items shifted this week" is more actionable than a full catalog comparison.

Links

• Pepesto API docs
• tesco-ie-vs-gb-price-gap.js