`.
---
## 6. Putting It All Together: Larger Example
Consider a blog site. We have a schema that extracts the **URL** from each post card (via `baseFields` with an `"attribute": "href"`), plus the title, date, summary, and author:
```python
schema = {
"name": "Blog Posts",
"baseSelector": "a.blog-post-card",
"baseFields": [
{"name": "post_url", "type": "attribute", "attribute": "href"}
],
"fields": [
{"name": "title", "selector": "h2.post-title", "type": "text", "default": "No Title"},
{"name": "date", "selector": "time.post-date", "type": "text", "default": ""},
{"name": "summary", "selector": "p.post-summary", "type": "text", "default": ""},
{"name": "author", "selector": "span.post-author", "type": "text", "default": ""}
]
}
```
Then run with `JsonCssExtractionStrategy(schema)` to get an array of blog post objects, each with `"post_url"`, `"title"`, `"date"`, `"summary"`, `"author"`.
---
## 7. Tips & Best Practices
1. **Inspect the DOM** in Chrome DevTools or Firefox’s Inspector to find stable selectors.
2. **Start Simple**: Verify you can extract a single field. Then add complexity like nested objects or lists.
3. **Test** your schema on partial HTML or a test page before a big crawl.
4. **Combine with JS Execution** if the site loads content dynamically. You can pass `js_code` or `wait_for` in `CrawlerRunConfig`.
5. **Look at Logs** when `verbose=True`: if your selectors are off or your schema is malformed, it’ll often show warnings.
6. **Use baseFields** if you need attributes from the container element (e.g., `href`, `data-id`), especially for the “parent” item.
7. **Performance**: For large pages, make sure your selectors are as narrow as possible.
---
## 8. Schema Generation Utility
While manually crafting schemas is powerful and precise, Crawl4AI now offers a convenient utility to **automatically generate** extraction schemas using LLM. This is particularly useful when:
1. You're dealing with a new website structure and want a quick starting point
2. You need to extract complex nested data structures
3. You want to avoid the learning curve of CSS/XPath selector syntax
### Using the Schema Generator
The schema generator is available as a static method on both `JsonCssExtractionStrategy` and `JsonXPathExtractionStrategy`. You can choose between OpenAI's GPT-4 or the open-source Ollama for schema generation:
```python
from crawl4ai.extraction_strategy import JsonCssExtractionStrategy, JsonXPathExtractionStrategy
from crawl4ai import LLMConfig
# Sample HTML with product information
html = """
"""
# Option 1: Using OpenAI (requires API token)
css_schema = JsonCssExtractionStrategy.generate_schema(
html,
schema_type="css",
llm_config = LLMConfig(provider="openai/gpt-4o",api_token="your-openai-token")
)
# Option 2: Using Ollama (open source, no token needed)
xpath_schema = JsonXPathExtractionStrategy.generate_schema(
html,
schema_type="xpath",
llm_config = LLMConfig(provider="ollama/llama3.3", api_token=None) # Not needed for Ollama
)
# Use the generated schema for fast, repeated extractions
strategy = JsonCssExtractionStrategy(css_schema)
```
### LLM Provider Options
1. **OpenAI GPT-4 (`openai/gpt4o`)**
- Default provider
- Requires an API token
- Generally provides more accurate schemas
- Set via environment variable: `OPENAI_API_KEY`
2. **Ollama (`ollama/llama3.3`)**
- Open source alternative
- No API token required
- Self-hosted option
- Good for development and testing
### Benefits of Schema Generation
1. **One-Time Cost**: While schema generation uses LLM, it's a one-time cost. The generated schema can be reused for unlimited extractions without further LLM calls.
2. **Smart Pattern Recognition**: The LLM analyzes the HTML structure and identifies common patterns, often producing more robust selectors than manual attempts.
3. **Automatic Nesting**: Complex nested structures are automatically detected and properly represented in the schema.
4. **Learning Tool**: The generated schemas serve as excellent examples for learning how to write your own schemas.
### Best Practices
1. **Review Generated Schemas**: While the generator is smart, always review and test the generated schema before using it in production.
2. **Provide Representative HTML**: The better your sample HTML represents the overall structure, the more accurate the generated schema will be.
3. **Consider Both CSS and XPath**: Try both schema types and choose the one that works best for your specific case.
4. **Cache Generated Schemas**: Since generation uses LLM, save successful schemas for reuse.
5. **API Token Security**: Never hardcode API tokens. Use environment variables or secure configuration management.
6. **Choose Provider Wisely**:
- Use OpenAI for production-quality schemas
- Use Ollama for development, testing, or when you need a self-hosted solution
That's it for **Extracting JSON (No LLM)**! You've seen how schema-based approaches (either CSS or XPath) can handle everything from simple lists to deeply nested product catalogs—instantly, with minimal overhead. Enjoy building robust scrapers that produce consistent, structured JSON for your data pipelines!
---
## 9. Conclusion
With **JsonCssExtractionStrategy** (or **JsonXPathExtractionStrategy**), you can build powerful, **LLM-free** pipelines that:
- Scrape any consistent site for structured data.
- Support nested objects, repeating lists, or advanced transformations.
- Scale to thousands of pages quickly and reliably.
**Next Steps**:
- Combine your extracted JSON with advanced filtering or summarization in a second pass if needed.
- For dynamic pages, combine strategies with `js_code` or infinite scroll hooking to ensure all content is loaded.
**Remember**: For repeated, structured data, you don’t need to pay for or wait on an LLM. A well-crafted schema plus CSS or XPath gets you the data faster, cleaner, and cheaper—**the real power** of Crawl4AI.
**Last Updated**: 2025-01-01
---
That’s it for **Extracting JSON (No LLM)**! You’ve seen how schema-based approaches (either CSS or XPath) can handle everything from simple lists to deeply nested product catalogs—instantly, with minimal overhead. Enjoy building robust scrapers that produce consistent, structured JSON for your data pipelines!
```