Website Categorization API: Get a content category for any domain

Get each domain's category in the IAB Content Taxonomy v3.1, the standard most ad-tech and brand-safety platforms use. The API reads the site, classifies it using a set of machine learning models, and returns up to three ranked categories.

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500 free API requests. No credit card required.

180M+Domains in the latest snapshot

704IAB v3.1 categories,
across 4 tiers

CSV + ParquetWith per-file manifests

52,000+Satisfied customers

What can you do with Website Categorization API

Categorize domains worldwide

Classify domains in the IAB Content Taxonomy v3.1, including websites with non-English content.
Protect brand safety

Check the content category of websites where ads may appear, so you can keep campaigns away from inappropriate, unsafe, or off-brand placements.
Power web filtering workflows

Turn category intelligence into allowlists, blocklists, parental controls, and acceptable-use policies.
Build smarter cybersecurity products

Add content-category context to cybersecurity products, helping customers apply browsing policies and understand the type of website behind a domain.

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Clear, machine-readable classifications

Get IAB v3.1 content categories with confidence scores for a domain. Switch format to get an additional OpenRTB object.

View API docs

Up to 100 domains per request
600 requests per minute by default

curl -X POST "https://website-categorization.whoisxmlapi.com/api/v4/categorize?apiKey=YOUR_API_KEY" \
     -H "Content-Type: application/json" \
     -d '{"domain": "stackoverflow.com"}'{
    "domain": "stackoverflow.com",
    "primary_category": {
        "iab_id": "IAB-599",
        "tier1": "Technology & Computing",
        "tier2": "Computing",
        "path": "Technology & Computing > Computing",
        "confidence": 0.94
    },
    "credits_charged": 1
}curl -X POST "https://website-categorization.whoisxmlapi.com/api/v4/categorize?apiKey=YOUR_API_KEY&output_mode=set&coverage=0.65" \
     -H "Content-Type: application/json" \
     -d '{"domain": "stackoverflow.com"}'{
    "domain": "stackoverflow.com",
    "primary_category": {
        "iab_id": "IAB-599",
        "tier1": "Technology & Computing",
        "tier2": "Computing",
        "path": "Technology & Computing > Computing",
        "confidence": 0.94
    },
    "credits_charged": 1,
    "prediction_set": {
        "set": [
            {
                "tier1": "Technology & Computing",
                "tier2": "Computing",
                "confidence": 0.94
            },
            {
                "tier1": "Business and Finance",
                "tier2": "Business",
                "confidence": 0.19
            }
        ]
    }
}curl -X POST "https://website-categorization.whoisxmlapi.com/api/v4/categorize?apiKey=YOUR_API_KEY&output_format=openrtb" \
     -H "Content-Type: application/json" \
     -d '{"domain": "stackoverflow.com"}'{
    "domain": "stackoverflow.com",
    "primary_category": {
        "iab_id": "IAB-599",
        "tier1": "Technology & Computing",
        "tier2": "Computing",
        "path": "Technology & Computing > Computing",
        "confidence": 0.94
    },
    "credits_charged": 1,
    "openrtb": {
        "cat": [
            "596",
            "599"
        ],
        "cattax": 9
    }
}curl -X POST "https://website-categorization.whoisxmlapi.com/api/v4/categorize?apiKey=YOUR_API_KEY&output_mode=set&coverage=0.65&output_format=openrtb" \
     -H "Content-Type: application/json" \
     -d '{"domain": "stackoverflow.com"}'{
    "domain": "stackoverflow.com",
    "primary_category": {
        "iab_id": "IAB-599",
        "tier1": "Technology & Computing",
        "tier2": "Computing",
        "path": "Technology & Computing > Computing",
        "confidence": 0.94
    },
    "credits_charged": 1,
    "prediction_set": {
        "set": [
            {
                "tier1": "Technology & Computing",
                "tier2": "Computing",
                "confidence": 0.94
            },
            {
                "tier1": "Business and Finance",
                "tier2": "Business",
                "confidence": 0.19
            }
        ]
    },
    "openrtb": {
        "cat": [
            "596",
            "599"
        ],
        "cattax": 9
    }
}

Standard JSON · Top category Returns the highest-ranked IAB v3.1 category.

Website Categorization API developer benefits

Structured output

Get a clean JSON response that is easy to work with: ranked categories, IAB IDs, tier-by-tier paths, confidence scores, and a primary category.
OpenRTB support

Add output_format=openrtb to a single-domain request to include an OpenRTB-ready version of the result in your response.
Policy groups

Use include=policy to map categories to 47 policy groups—the labels used in DNS filtering, secure web gateways, and endpoint controls.
Single & bulk requests

Need one answer? Send one domain. Need more? Classify up to 100 domains in one request.

View API docs

Give your AI agent website categorization capabilities

Connect the WhoisXML API MCP server to Claude, Cursor, VS Code, or another MCP client. Then ask to classify a website in plain words or have your AI agents do it for you.

Connect the MCP server

Hosted MCP server (Streamable HTTP, OAuth)

https://mcp-hosted.whoisxmlapi.com/mcp

Add WhoisXML API from your client’s connectors, or paste the URL as a custom connector
Sign in once with your API key
Ask your agent. Website Categorization is one of the 20+ tools it can use

Works with Claude, Cursor, VS Code and other MCP clients

Website Categorization Database

Apply for early access to our website categorization database.

Apply for Early Access

Questions developers ask

What taxonomy does Website Categorization API use?: It returns categories from the IAB Content Taxonomy v3.1: 704 categories across four tiers.
Can I classify multiple domains?: Yes. The bulk endpoint classifies up to 100 domains in one synchronous call, and only domains that return a result are charged. See the bulk requests documentation for details.
Will every domain receive a category?: Not always. If the API cannot read a site, it may return no category. No-category results do not consume a credit.
How many requests can I send?: The default limit is 600 requests per minute per API key, or about 10 requests per second on average.
Are cached or failed requests billed?: A classification that returns a category costs one credit, including cached results. No-category results, errors, rate-limited requests, and the taxonomy endpoint are not billed.

Still have questions? Read the API docs or contact us.

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Raffaele Sommese

Researcher

University of Twente

“As part of my research into establishing resilience and security properties within the domain name infrastructure of the broader Internet, I was pleased to use the WhoisXML API Website Categorization service to identify the business categories of affected infrastructure. Integrating the APIs into my research workflow was seamless, thanks to the clear and comprehensive documentation available on their website. Within minutes, I was able to begin classifying websites and gain deeper insights into the types of businesses impacted by resilience gaps and security-related incidents.”

Sergio Diaz

Master in Cybersecurity Student

Carlos III University of Madrid

“WhoisXML API’s Website Categorization API helped me save time. If I did not use it, I would still be categorizing domains manually. It also improved the study’s accuracy, as the API had well-defined categories, and the output is precise and relevant.”

Dennis Suermann

Student

University of Paderborn, System Security department

“The website intelligence is easy to set up and returns everything we need. One reason for this is the documentation of the API, which is well-written and very detailed.”

Marzieh Bitaab

PhD Student, Computer Science

Arizona State University

“Thanks to well-structured and clear API documentation provided by WhoisXML API, we were able to integrate the solution seamlessly into our system with minimal technical challenges.”

Fergus Smith

Software Development MST Student

University of Glasgow

“With other APIs, there’s a tendency for requests to fail. But I didn’t notice that with Website Categorization API. I noticed that whenever a request was made, the website was always categorized.”

Mohammad Ismail Daud

Student

UC Davis

“I used WHOIS API and Website Categorization API. Both tools are simple and straightforward to use. Some API providers have extra bells and whistles that they force you to use, but WhoisXML API is really easy to work with. It’s stable, and I can trust that it’s not going to flatline later.”

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Website Categorization API: Get a content category for any domain

What can you do with Website Categorization API

Categorize domains worldwide

Protect brand safety

Power web filtering workflows

Build smarter cybersecurity products

Clear, machine-readable classifications

Website Categorization API developer benefits

Structured output

OpenRTB support

Policy groups

Single & bulk requests

Give your AI agent website categorization capabilities

Website Categorization Database

Questions developers ask

What taxonomy does Website Categorization API use?

Can I classify multiple domains?

Will every domain receive a category?

How many requests can I send?

Are cached or failed requests billed?

Get 500 free API requests. No credit card required.

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