Advanced5 steps

How to Build a Price Comparison Tool

Comparing prices across multiple retailers requires fetching product pages from different sites simultaneously, normalizing diverse price formats, and matching the same product across different naming conventions — all on a recurring schedule.

Step-by-Step Guide

1

Define your product catalog

Create a list of products with their URLs on each retailer you want to monitor. Use a consistent product identifier (SKU, GTIN) to match products across sites.

2

Build site-specific extractors

Write a selector configuration for each retailer's price element. Store these as a dictionary keyed by domain so you can apply the right extractor per URL.

3

Fetch prices in parallel

Use AlterLab's batch endpoint to fetch multiple product URLs simultaneously, reducing total collection time.

4

Normalize and compare

Convert all prices to a common currency and decimal format. Sort by price to find the cheapest option and flag significant price changes.

5

Schedule and alert

Run comparisons on a schedule. Send alerts when a tracked product drops below a price threshold.

Code Example

Python
import requests
from bs4 import BeautifulSoup

RETAILER_SELECTORS = {
    "example-store-a.com": ".product-price",
    "example-store-b.com": "#price-display",
}

def get_price(url: str, api_key: str) -> str | None:
    from urllib.parse import urlparse
    domain = urlparse(url).netloc.replace("www.", "")
    selector = RETAILER_SELECTORS.get(domain)
    if not selector:
        return None

    response = requests.post(
        "https://alterlab.io/api/v1/scrape",
        headers={"X-API-Key": api_key, "Content-Type": "application/json"},
        json={"url": url, "render_js": True},
    )
    html = response.json().get("html", "")
    el = BeautifulSoup(html, "html.parser").select_one(selector)
    return el.get_text(strip=True) if el else None

Replace YOUR_API_KEY with your key from the . No credit card required.

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Frequently Asked Questions

How do I handle price variations (sizes, colors)?

For variable products, you may need to scrape each variant URL separately or intercept the XHR requests that return variant pricing data from the product page JavaScript.

Responsible Use

AlterLab is designed for extracting publicly available data. Always review the terms of service for any website you access, respect robots.txt directives, and ensure your use case complies with applicable laws in your jurisdiction.

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terminal
curl -X POST https://api.alterlab.io/v1/scrape \
-H "X-API-Key: YOUR_KEY" \
-H "Content-Type: application/json" \
-d '{"url": "https://example.com", "formats": ["markdown"]}'

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