Shadow
Shadow: A free, deterministic Linux simulator for testing unmodified networked applications. Ranked #20 of 30 in Network Simulation Software by our editors (7.2/10); pricing: Free plan; best for deterministic Linux application experiments.
At a glance
- Editor score7.2 / 10
- PricingFree plan
- Best forDeterministic Linux application experiments
- Free planYes
- Paid fromFree
- Real-time emulationNo
- Facts checked20 Sep 2026
Where it wins
- Runs unmodified Linux application binaries as simulated network processes
- Models topology, routing, latency, loss, bandwidth, TCP and UDP
- Deterministic, isolated experiments with multithreading and PCAP output
Where it doesn't
- Linux-only platform support
- Does not provide real-time emulation
- Requires local installation and execution on Linux systems
Our verdict on Shadow
Shadow is an open-source network experimentation tool for researchers and developers testing distributed, networked applications. It runs unmodified application binaries as native Linux processes, connects them through an internally simulated network, and models simulated TCP and UDP networking. Its audience is teams that need repeatable application experiments without connecting test traffic to the real network. The product is distributed as a Linux command-line application for use on laptops, desktops, and servers.
Shadow’s strongest fit is its controlled simulation model. Users can define network topology and routing, then configure latency, packet loss, and bandwidth while advancing simulated time through a discrete-event engine. Seeded randomness supports deterministic, reproducible experiments, and the private network environment isolates simulated activity from the real network. Multi-threaded simulation supports multiple virtual hosts, while PCAP packet capture output provides a concrete record of simulated traffic. An automation API is also listed, supporting repeatable workflows around experiments.
The pricing model is open source with a free plan, making Shadow accessible without a paid tier structure. That value comes with a focused operating boundary: the supported platform is Linux, and real-time emulation is not included. Shadow is therefore a strong choice for deterministic experiments involving real Linux application binaries, configurable network conditions, and reproducible results. Teams that need cross-platform operation, real-time behavior, or a broader deployment model should look for a different type of network simulation tool.
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Shadow pricing
Shadow fact sheet
| Free plan | Yes |
|---|---|
| Paid from | Free |
| Simulation model | Hybrid |
| Real-time emulation | No |
| Hardware-in-the-loop | Not verified |
| Deployment options | Not verified |
| Documented node limit | Not verified |
| Automation API | Yes |
| Deployment | Self-hosted |
| Platforms | Linux |
| Support | Community, Docs |
| Built for | Solo, Small business, Mid-market (editorial estimate) |
| Pricing | Free plan |
| Website | shadow.github.io |
| Facts checked | 20 Sep 2026 |
Alternatives to Shadow
- GNS3A free, broad multivendor lab for simulating, emulating, and connecting real networks.9.4
- Cisco Modeling LabsA Cisco-focused virtual lab with broad automation, integration, and deployment options.9.2
- EVE-NGA broad emulation platform for large, collaborative multivendor network labs.9.0
Also Ranked In
Shadow is ranked in 2 of our directories.
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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
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