Beginner4 steps

How to Extract Structured Data from HTML

Raw HTML contains the data you need buried in nested tags, inconsistent formatting, and multiple possible locations. Extracting clean, structured output requires a systematic approach using CSS selectors, JSON-LD parsing, or table extraction.

Step-by-Step Guide

1

Fetch the page HTML

Use AlterLab to retrieve the fully rendered HTML, including any content loaded via JavaScript.

2

Check for embedded JSON-LD

Many product and article pages embed structured data in JSON-LD script tags. Parse these first — they often contain exactly the fields you need in clean JSON format.

3

Fall back to CSS selector extraction

For pages without JSON-LD, use CSS selectors with BeautifulSoup or lxml to target specific elements. Inspect the page in browser DevTools to find reliable selectors.

4

Normalize and clean extracted values

Strip whitespace, remove HTML entities, and convert types (strings to numbers, date strings to datetime objects) before storing your data.

Code Example

PythonGet free API key →
import requests
import json
from bs4 import BeautifulSoup

def extract_structured(url: str, api_key: str) -> dict:
    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", "")
    soup = BeautifulSoup(html, "html.parser")

    # Try JSON-LD first
    for script in soup.find_all("script", type="application/ld+json"):
        try:
            data = json.loads(script.string)
            if data.get("@type") in ("Product", "Article"):
                return data
        except (json.JSONDecodeError, AttributeError):
            continue

    # Fall back to CSS selectors
    return {
        "name": soup.select_one("h1")?.get_text(strip=True),
        "price": soup.select_one("[data-price]")?.get("data-price"),
    }

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

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Frequently Asked Questions

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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    How to Extract Structured Data from HTML | AlterLab | AlterLab