Use with authorization only. Scan networks and hosts you own or have explicit written permission to assess. Unauthorized scanning can violate acceptable-use policies and, in some jurisdictions, the law.

Overview

Masscan is an open-source port scanner developed by Robert Graham. It is designed around a single goal: scanning very large ranges of IP addresses for open ports as quickly as possible. To achieve this, Masscan implements its own asynchronous transmission and reception logic with a custom TCP/IP stack, rather than relying on the operating system’s standard networking stack for each connection. This architectural choice allows it to reach much higher scan rates than traditional synchronous scanners when configured to do so.

Key capabilities

Masscan’s core capability is asynchronous TCP port scanning at high packet rates, allowing it to cover large address spaces, including ranges as broad as the full IPv4 address space, in a relatively short amount of time when run with a sufficiently high transmission rate. It supports command-line syntax that overlaps with Nmap for many common options, which makes it more approachable for users already familiar with that tool, though its underlying scanning engine and internal behavior are distinct. Masscan can output results in a variety of formats suitable for further processing or integration with other tools and workflows.

Because Masscan generates traffic at very high rates, it is capable of overwhelming network equipment, intrusion detection systems, or the target hosts themselves if not configured carefully. This makes rate control and scope configuration especially important when using the tool.

Typical use cases

Masscan is typically used by network administrators and security researchers who need to survey large numbers of hosts or entire network ranges for open ports in a short time frame, such as during large-scale authorized security assessments or asset discovery across sizable IP allocations. It is commonly paired with slower, more detailed tools like Nmap, which can be used afterward to perform in-depth service and version detection on the hosts and ports that Masscan identifies as open. Because of its speed and scale, Masscan must only be run against networks and hosts that you own or have explicit, documented authorization to test. Its high packet rate means misuse can disrupt production networks, trigger security alerts, and in many jurisdictions constitute a violation of computer misuse laws; users are responsible for ensuring their scanning activity is authorized and appropriately scoped and rate-limited.

Licensing and pricing

Masscan is open-source software distributed under the GNU Affero General Public License version 3 (AGPLv3). It is free to download, use, and modify in accordance with the terms of that license.

Platform support

Masscan is primarily developed and used on Linux, where its custom networking approach is best supported. It can also be built from source on macOS and Windows, though functionality and performance on those platforms may differ from the primary Linux target.

Getting started

Masscan is distributed as source code through its official repository at github.com/robertdavidgraham/masscan. This catalog does not host installers or pre-built binaries and does not distribute the software directly; consult the repository for build instructions specific to your platform. Before running any scan, confirm that you own the target network or hosts or have explicit authorization to test them, and configure the scan rate conservatively to avoid unintended disruption to networks or services.

Where to download

Downloads are hosted by Robert Graham on their official website. The button below opens that site — we never host installers.

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