Choosing the right scanner depends on what you’re trying to achieve. If you just need a quick, one-off sweep, a free open‑source tool may be fine. If you’re consolidating internal discovery, external attack surface management (EASM), and cloud visibility for an enterprise program, you’ll want a platform that scales, unifies data, and produces evidence you can use.
This guide compares popular free tools and outlines when to move to a unified platform. It also shows the fastest way to get full internal/external visibility with runZero.
Here’s how the most-used free tools stack up for security teams.
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Nmap (with Zenmap)
Tradeoffs: CLI can be complex; needs scripting and a database for continuous use; can upset fragile OT/IoT; not built for multi-site inventory.
Angry IP
Tradeoffs: Minimal asset detail; not scalable; can disrupt sensitive devices.
Masscan
When to use them together - Keep Nmap/Angry IP/Masscan for targeted, tactical jobs. - Use runZero as your system of record and continuous discovery engine to centralize results and context across internal, external, and cloud assets.
If you’re consolidating vulnerability management (VM) visibility, EASM, and cloud security data:
Adds rich context (services, misconfigurations, weak controls, segmentation gaps) that VM tools often miss. See how we “go beyond CVEs” on the vulnerability management page.
Keep EASM data sources in the mix
Pair runZero’s external discovery with Shodan/Censys integrations to find and enrich internet-facing assets your ASNs or domains might miss.
Avoid relying solely on legacy VM suites for visibility
For corporate security teams, runZero is the most complete way to see the entire attack surface—inside and out—fast.
What sets it apart - Total coverage, no blind spots - Agentless discovery across IT, OT, IoT, cloud, mobile, and remote—plus public-facing assets by domain, ASN, IP, and FQDN. - Advanced fingerprinting and exposure insight - Identifies OS, hardware, services, misconfigurations, weak controls, risky ports, shared keys, EOL software, and more. - External ASM built in - Discover public hosts, enrich with Shodan/Censys, grab screenshots, and generate an External Assets Report for auditors and execs. - Verification of segmentation and attack paths - New 4.9 capabilities add enhanced topology and attack path mapping to spot chokepoints and segmentation gaps before attackers do. See what’s new in 4.9 - Enterprise readiness - Multi-tenant, distributed Explorers, role-based access, scheduling, alerting, dashboards, and exportable evidence for audits and risk assessments.
Proof from practitioners - “We definitely found a lot more assets with runZero… it’s like turning the light on and now you can see everything.” — Paul Wescott, Security Architect, University of Auckland. Read more on our testimonials page. - Independent review: Watch Tom Lawrence’s overview of runZero’s discovery and reporting. Watch the review
You can go from zero to a unified internal/external inventory in minutes—without agents or credentials.
1) Kick off external discovery - Add Shodan or Censys integrations to pull likely public assets for your organization. - Start a hosted scan from a cloud “Hosted zone” (no on-prem server needed). - Scope by: - Domain: e.g., domain:example.org (discovers subdomains and hosts with matching TLS CNs) - ASN: e.g., asn4:12345 (all IPs assigned to your ASN) - Public assets found via integrations: public:all - Schedule imports/scans and set alerts (e.g., “new-assets-found”) to be notified of changes post-scan. - How-to details: Read our guide on scanning your external attack surface.
2) Expand to internal networks and cloud - Deploy Explorers to remote sites/VPCs/VNETs for distributed scanning at scale. - Connect cloud and security tools to enrich asset context (EDR, MDM, directories, vulnerability scanners, SIEM/CMDB).
3) Verify segmentation, controls, and risk—and export evidence - Use topology and attack path views to spot risky lateral movement and segmentation gaps. - Run built-in queries to flag EOL software, shared SSH keys, exposed databases, private IP leakage on public hosts, and more. - Generate the External Assets Report, software/product inventories, and dashboards for auditors and risk reviews. Schedule and email reports or export to PDF.
Result: a living, queryable inventory across internal, external, cloud, and OT/IoT—plus the context to prioritize and prove remediation.
Use these tactically, but centralize the results and ongoing visibility in runZero so your team has one source of truth, enterprise reporting, and alerting.