Is Common Crawl data free to use?

Yes. Common Crawl data is freely available to anyone for any purpose. The datasets are hosted on Amazon S3 as part of the AWS Open Data program, which means you can access and download the data without paying storage fees. You only pay for compute if you process the data on AWS infrastructure. Researchers, startups, and enterprises all use Common Crawl data without licensing costs.

How often does Common Crawl update its dataset?

Common Crawl completes a new crawl approximately once per month. Each monthly crawl captures 2 to 3 billion web pages and generates around 200 to 400 terabytes of data. Historical crawl archives dating back to 2008 remain available, giving users access to over a decade of web snapshots for longitudinal analysis and research.

Can you opt out of Common Crawl?

Yes. Website owners can use their robots.txt file to block the CCBot user agent, which is the crawler Common Crawl uses. Adding 'User-agent: CCBot' followed by 'Disallow: /' to your robots.txt file prevents Common Crawl from indexing your site in future crawls. However, pages already captured in past crawl archives will remain in those historical datasets.

How is Common Crawl different from Google's web index?

Common Crawl is a static dataset of raw web page content released in monthly batches. Google's index is a continuously updated, processed search database used to serve search results in real time. Common Crawl captures raw HTML and metadata for research purposes while Google's index involves deep content understanding, ranking signals, and real-time freshness. Common Crawl data is public while Google's index is proprietary.

What Is Common Crawl?

Common Crawl is a nonprofit organization that builds and maintains the largest publicly available dataset of web crawl data in the world. Since 2008, it has been systematically crawling the web and releasing the resulting data for free - making billions of web pages accessible to researchers, developers, and companies who would otherwise lack the resources to crawl the web at that scale. As of 2025, the Common Crawl corpus contains over 250 billion web pages collected across more than 15 years of monthly crawls.

The significance of Common Crawl extends far beyond academic research. It has become one of the foundational training datasets for virtually every major large language model, including GPT-4, Claude, LLaMA, and PaLM. If you have used an AI chatbot or search engine in the past two years, the answers it gave you were shaped in part by data Common Crawl collected.

How Does Common Crawl Work?

Common Crawl operates a web crawler called CCBot that systematically visits websites across the internet, downloads their content, and stores it in a structured format. The process follows a cycle:

Seed URL selection. Each crawl begins with a list of seed URLs drawn from previous crawls, web directories, and submitted URLs. The crawler prioritizes widely linked and frequently updated pages.

Crawling. CCBot visits each URL, downloads the HTML content, and follows links to discover new pages. The crawler respects robots.txt directives - site owners can block CCBot by specifying it in their robots.txt file.

Data storage. The crawled data is stored in three formats on Amazon S3. WARC (Web ARChive) files contain the raw HTTP responses including headers and full page content. WAT files contain computed metadata extracted from the WARC data. WET files contain extracted plain text with all HTML markup removed.

Public release. Each monthly crawl is published as a free, downloadable dataset. A single crawl typically captures 2 to 3 billion web pages and generates 200 to 400 terabytes of uncompressed data.

The entire archive is hosted through the AWS Open Data program, meaning anyone can access it without paying storage costs. Processing the data requires compute resources, but the data itself is free.

Why Does Common Crawl Matter for AI?

Common Crawl's role in AI development cannot be overstated. When researchers at OpenAI, Google, Meta, and Anthropic train large language models, they need enormous amounts of text data to teach the model how language works, what facts exist, and how to reason about information.

Common Crawl provides the largest single source of that training text. The C4 dataset (Colossal Clean Crawled Corpus) - a filtered and cleaned version of Common Crawl data created by Google - was used to train the T5 model and became a standard training dataset across the industry. Meta's LLaMA models used Common Crawl as approximately 67 percent of their training data.

This means that if your website has been indexed by Common Crawl, its content has likely influenced how AI models understand and generate text about your topic. For businesses focused on AI visibility, this creates both an opportunity and a consideration:

The opportunity. Content captured by Common Crawl becomes part of the knowledge base that AI models draw from. High-quality, authoritative content on your website can influence how AI systems represent your topic area and potentially your brand.

The consideration. Once your content is in a Common Crawl archive, it remains there permanently. Historical crawl data is not deleted even if you later block CCBot in your robots.txt. Organizations concerned about their content being used for AI training need to weigh this when deciding whether to allow Common Crawl access.

How Is Common Crawl Used Beyond AI Training?

While AI training is the most prominent use case today, Common Crawl serves many other purposes:

Academic research. Linguists, social scientists, and computer scientists use Common Crawl data to study web content patterns, language usage, misinformation spread, and internet evolution. The longitudinal nature of the archive - spanning over 15 years - makes it uniquely valuable for studying how the web changes over time.

Web scraping alternatives. Companies that need large-scale web data can use Common Crawl instead of building their own crawling infrastructure. This is particularly valuable for startups that need web-scale data but cannot afford to run their own crawlers at that level.

SEO and content analysis. Common Crawl data can be used to analyze backlink patterns, content structures, keyword distributions, and competitive landscapes at scale. Several commercial SEO tools incorporate Common Crawl data into their link databases and site analysis features.

Language model evaluation. Researchers use Common Crawl snapshots to build test datasets for evaluating how well AI models handle different types of web content, languages, and domains.

Data journalism. Journalists use Common Crawl archives to investigate how websites have changed over time, track the spread of online content, and analyze web-scale trends that would be impossible to study manually.

How Does Common Crawl Relate to Robots.txt and Crawl Control?

Common Crawl respects robots.txt directives, which means website owners have control over whether CCBot crawls their site going forward. To block Common Crawl, add the following to your robots.txt file:

User-agent: CCBot
Disallow: /

This is the same mechanism used to control other crawlers like GPTBot and Google's crawlers. The key difference is that blocking CCBot only affects future crawls - pages already captured in historical archives remain in those datasets.

The decision to block CCBot involves trade-offs. Blocking it prevents your content from appearing in future crawl archives and reduces the chance of it being included in future AI training datasets. But it also removes your content from a dataset used by researchers, tools, and systems that might reference or link back to your site.

For most businesses, the practical impact of blocking CCBot is minimal unless you publish large volumes of proprietary content or have specific concerns about AI training data usage. The content is already publicly available on your website - Common Crawl simply creates a structured, downloadable copy of it.

What Should Startups Know About Common Crawl?

For startups building their online presence, Common Crawl is relevant in several ways:

Your content enters AI training pipelines. If CCBot can access your site, your content will likely end up in future AI training datasets. Publishing clear, authoritative, well-structured content increases the chance that AI models accurately represent your expertise and domain.

Competitor analysis at scale. Common Crawl data lets you analyze competitor websites, content strategies, and link profiles without running your own crawler. Several open-source tools exist for querying Common Crawl's index to extract data about specific domains.

Data for your own products. If you are building data-driven features or AI-powered tools, Common Crawl provides a massive, free dataset to bootstrap your development. Many startups have built products - from search engines to content analysis tools - on top of Common Crawl data.

Common Crawl represents an important piece of the web's infrastructure. It democratizes access to web-scale data that was previously only available to companies with massive crawling budgets, and it plays a foundational role in shaping how AI systems understand and generate information about the world.