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Knowledge base

Web Filtering Knowledge Base

Plain explanations of how web filters work, how category data gets into products, and how to filter specific networks.

Web filtering basics

What each kind of filter can see, what it can block and where it falls short.

What Is URL Filtering? How Category Databases Power Web FiltersHow a web filter decides, and how categories, blocklists and reputation compare. What is DNS filtering?How a DNS filter checks each lookup against domain categories, its limits and bypass routes. What is a secure web gateway?How a gateway filters by URL category, inspects HTTPS and files, and compares to DNS filtering. DNS Filtering vs Web Filtering: What Each Can BlockWhat DNS blocking can and cannot see, HTTPS limits, and when to combine both methods. DNS over HTTPS and web filteringWhy encrypted DNS can slip past DNS filters and how admins keep filtering working. SSL inspection and URL categories: what to decrypt and what to leave aloneWhich categories to exempt from decryption, what SNI and ECH change, and a decision flow. Content Filtering CategoriesThe full category taxonomy, organised into security, adult, lifestyle, business and other groups. Web Filtering Software for Business: What Separates Good FiltersA buyer's guide to coverage, update speed, false positives, deployment and reporting.

Category data, feeds and APIs

How domains get classified, kept current and delivered as files or lookups.

Domain Categorization APIHow the lookup API included with a database licence works next to the downloadable file. Bulk Domain Classification APIClassify thousands of domains at once with batch uploads, async processing and callbacks. Real-Time URL ClassificationHow newly registered domains are classified daily and checked again after a week and a month. Streaming Classification APIHigh throughput, event driven domain classification for resolvers, proxies and firewalls. Machine Learning ClassificationThe text, image and graph models behind domain classification and how they keep learning. Phishing and Malware Domain Feed for Firewalls and DNS FiltersA daily feed of new risky domains, rechecked over time and delivered as delta files. Blocklist Formats: CSV, Hosts, DNS RPZ and Firewall EDLEach blocklist format explained with examples, and which filtering tool expects which. Safe Browsing APIURL reputation checks and unsafe content warnings for browsers and apps.

Building category data into products

Notes for product teams adding URL categories to security, device and software products.

DNS Filtering IntegrationConnect a web filtering database to common DNS resolvers for category based filtering. Content Risk Intelligence IntegrationFeed category data into SIEM, SOAR, gateway, DNS and proxy stacks for risk scoring. Content Classification IntegrationHow content classification detects unsafe content and command servers, with feed update rates. URL Categorization for Email Security ProductsLink risk signals and key categories for delivery time and time of click checks. URL Category Guardrails for AI Agents That Browse the WebAllow, approve and deny tiers that keep browsing AI agents away from risky sites. URL Category API for SaaS ProductsFeatures URL categories enable in a SaaS product, and API versus licensed database. Content Filter Data for Browser ExtensionsRule limits, local lists versus lookups and the categories an extension filter needs. Web Content Filter Data for MDM ProductsEnforcement points and categories per device group for device management products. Router content filtering for OEMsBuild category filtering and parental controls into router and mesh firmware. URL Category Data for SASE PlatformsOne category store for gateway, DNS, firewall and cloud app controls across every point of presence. URL Category Data for ZTNASplit tunnel rules, agent lists and trust signals for zero trust network access products. URL Category Data for Secure Enterprise BrowsersPaste, upload and download controls by category, shipped inside the browser policy. URL Category Data for DLPUpload destination tiers for AI tools, personal storage and file sharing in data loss prevention. URL Category Data for XDRLabel every domain in your telemetry to sharpen detections, hunting and investigations. URL Category Data for Security Posture ManagementRank risky webhooks, forwarding rules, egress lists and AI apps found in configurations. URL Category Data for Human Risk ManagementRisky browsing signals, phishing simulation context and coaching nudges for awareness platforms. URL Category Data for Threat ResearchIndicator enrichment, noise filtering and infrastructure pivots for research teams. URL Category Data for MSSPsOne category set across mixed client estates for SOC triage, hunting and client reports. URL Category Data for Digital Risk ProtectionTriage lookalike domains, fake shops and leak sites, and catch the switch from parked to live. URL Category Data for OT and Industrial NetworksZone egress policy, unexpected destination alerts and offline updates for plants. URL Category Data for Mobile CarriersSecurity add-ons, family lines, business and IoT policy, and privacy-aware traffic analytics.

Family safety and education

Category data for parental control apps, screen time tools and school products.

Category Database for Parental Control AppsAge based category sets, AI tool and social media control, on the device or in the cloud. Parental Control SDK Category DataWhich categories an SDK should ship, files versus lookups, and integration steps. Family Web Filter and Parental ControlsAge based profiles, time schedules and activity reports for family web filtering. Website Categories for Screen Time AppsCategories that power time reports and limits in digital wellbeing apps. SafeSearch Enforcement Guide for Filtering ProductsDNS rewrites, headers, search engine coverage and the gaps category data closes. CIPA Web Filter for EducationWhat edtech and school filter makers need from a categorized domain database.

Business, compliance and ISP filtering

Policy design for companies and service design for internet providers.

DNS filtering for businessBuild a policy by team, roll it out in phases, close bypass routes and report usage. Enterprise Web Filtering and SecurityAcceptable use enforcement, data loss prevention and shadow IT detection for large companies. Custom Policy ManagementCategory groups, allow and block lists, per group rules, schedules and admin overrides. CIPA Web Filtering and ComplianceAudit logging, reporting and documentation for CIPA, GDPR, HIPAA and PCI DSS. Web filtering for small officesA one afternoon setup for offices of 2 to 50 people, including hybrid staff. ISP Content FilteringCarrier grade filtering with clean pipe services, subscriber management and parental controls. ISP-level content filteringNetwork, router and app filtering compared, with per subscriber DNS policy and opt-in models.

Guest Wi-Fi and community venues

Practical filtering setups for public, guest and community networks.

Guest Wi-Fi content filteringWhat to block on guest networks, ready made profiles, captive portal and DNS setup. Hotel Wi-Fi content filteringFiltering by zone for guest rooms, lobby, kids club, conference rooms and staff. Retail and restaurant customer Wi-Fi filteringCustomer Wi-Fi for shops, cafes and malls, with card payment separation and franchise rollout. Coworking space web filteringSecurity first categories, per member networks and abuse complaints in flexible offices. Web filtering for healthcare guest networksPatient and visitor Wi-Fi in hospitals and care homes, kept apart from clinical systems. Public library Wi-Fi filtering outside the USHow library filtering rules in the UK, EU, Australia, Canada and New Zealand differ from CIPA. Web filtering for churches and faith groupsProfiles for youth rooms and guest Wi-Fi in churches, mosques, synagogues and faith groups. Web filtering for youth organizationsAge based profiles and camp Wi-Fi setup for youth clubs, camps and after school programs.

Looking for step by step blocking instructions?

The blocking guides cover single apps, site types and devices. Ready made domain lists show what each blocklist contains.

Researchers can start with our web filtering research dataset.