Litmus

The Professional Network Speed Test

A free, professional-grade network speed test and iperf alternative. Measure bandwidth, latency, jitter, packet loss, and data integrity between two machines — with automatic quality grading and PDF reports. Available for Windows and Linux, no runtime required.

Windows DesktopLinux CLI

What Litmus Measures

Go beyond basic speed tests and iperf output. Every Litmus test produces a complete picture of network health with real-time metrics and professional-grade analysis.

Throughput

Average, minimum, and maximum bits per second across the test window.

Latency

Idle (pre-test baseline), loaded (during test), and post-test recovery measurements.

Jitter

RFC 3550 interarrival jitter calculation with per-sample timeline tracking.

Packet Loss

Per-packet sequence tracking with timestamped loss event detection.

Data Integrity

CRC32 verification — per-packet on UDP, stream-level on TCP.

Quality Score

Composite A through F letter grade derived from five weighted metrics.

Litmus vs iperf3 vs Online Speed Tests

See how Litmus compares to iperf3 and browser-based speed test tools like Speedtest.net and Fast.com.

FeatureLitmusiperf3Online Speed Tests
Throughput (bandwidth) testing
Latency measurement
Idle, loaded & recovery
Ping only
Jitter (RFC 3550)
Packet loss tracking
Per-packet timestamped
Summary only
Data integrity (CRC32)
Quality grading (A–F)
PDF reports
Automatic
GUI (desktop app)
Windows WPF
CLI only
Browser
CLI / headless mode
Real-time charts
5 chart styles
Basic
DSCP / QoS marking
Bandwidth shaping
Kbit–Tbit
Tests your actual network path
Tests to ISP only
No account or sign-up
Ads / tracking

Test Any Configuration

Mix and match protocols, directions, and stream counts to test exactly the scenario you need.

Protocol

  • TCP
  • UDP
  • Both (sequential)

Direction

  • Upload
  • Download
  • Bidirectional

Streams

  • 1–8 parallel connections
  • Per-stream tracking
  • Live aggregation

Certification Mode

One-click test suite that runs all six protocol/direction combinations in sequence, compiling results into a single certification PDF report with per-test grades and an overall pass/fail determination.

1.TCP Upload
2.TCP Download
3.TCP Bidirectional
4.UDP Upload
5.UDP Download
6.UDP Bidirectional

Network Quality Score

Every test receives a composite letter grade derived from five weighted metrics using a quadratic scoring curve.

Weighted Metrics

Bandwidth Stability35%

Threshold: min/max variance

Latency30%

Threshold: 100 ms

Jitter15%

Threshold: 10 ms

Packet Loss10%

Threshold: 0.05%

Data Integrity10%

Threshold: 0 corrupt packets

Grade Scale

A
Score: 90–100
B
Score: 75–89
C
Score: 60–74
D
Score: 40–59
F
Score: < 40

Scoring uses a quadratic curve — small deviations have minimal impact while values approaching the threshold drop the score sharply.

Professional Reports & Export

Automatic PDF report generation after every test, available in light and dark mode.

Standard Report

  • Hero throughput banner
  • Side-by-side config and quality summary
  • Letter grade badge
  • Throughput chart
  • Full metric breakdown

Certification Report

  • Multi-test summary with per-test grades
  • Pass/fail shields
  • Overview grid of all 6 tests
  • Individual test detail pages
  • Generated via --certify flag

Sample Reports

Standard Report

See what a single-test report looks like: TCP download at 4.96 Gbps with Grade A quality scoring, throughput charts, and full metric breakdown.

View Sample Report

Certification Report

Preview a full network certification: 6 tests across TCP & UDP (download, upload, bidirectional) on a 250 Mbps link, with per-test pass/fail results and charts.

View Certification Report

JSON Export

Structured output with config, per-interval samples, and full result summary

CSV Export

One row per sample: timestamp, bitrate, direction, latency, jitter, and more

Advanced Controls

More control than iperf3 or any speedtest app — fine-tune every aspect of your tests with professional-grade configuration options.

Bandwidth & Traffic

  • Bandwidth shaping (Kbit–Tbit)
  • DSCP/QoS marking (0–63)
  • Socket buffer size override
  • Warmup omit (0–60 seconds)

UDP Controls

  • Packet size (68–65,535 bytes)
  • Don't Fragment bit
  • Ramp-up pacing (0–2,000 ms)
  • Auto-detect ramp-up duration

Test Termination

  • Duration-based (seconds)
  • Byte count (K/M/G suffixes)
  • Packet count (UDP)
  • Interface binding

Data Patterns

  • Random (cryptographic)
  • Zeros / Ones / Alternating
  • Incrementing sequence
  • Microwave stress & custom byte

Charts & Visualization

  • Area, Line, Bar, Step, Gauge styles
  • 500 ms sample updates
  • Up to 4 simultaneous test runs
  • Auto-detect MTU (binary search)

Server & Network

  • Active connection monitoring
  • CPU usage with alert thresholds
  • Peer discovery & chat (LAN)
  • Server uptime & transfer statistics

Download Litmus

Download this free network speed test tool — self-contained executables, no runtime or dependencies required.

Windows

Windows 10/11 (64-bit)

Full-featured WPF desktop application with real-time charts, tabbed interface, and settings dialog.

Litmus.exe|191 MB

v1.0.3

Linux

x86_64 binary

Terminal application with interactive TUI, headless mode, and JSON output for automation.

litmus-x64|100 MB

v1.0.3

Windows SmartScreen Notice

Because Litmus is a new product with a self-signed certificate, Microsoft SmartScreen may flag the download as “unknown” and show a warning when you first run it. This is normal for any newly published software and only happens once — after you allow it the first time, Windows will not prompt again.

To verify the file is authentic, right-click Litmus.exe, select Properties → Digital Signatures → Details → View Certificate, and confirm the certificate thumbprint matches:

40f00afbb53179e8f366132eb808954a8c9c4333

Quick Start

# Download (Linux)

wget https://bobpopcorn.com/tools/litmus-x64 && chmod +x litmus-x64

# Start a server

./litmus-x64 -s

# 60-second TCP download test

./litmus-x64 -c 192.168.1.100 -t 60

# 8 parallel UDP streams

./litmus-x64 -c 192.168.1.100 --udp -P 8 -l 1500

# Bidirectional test with 1G target

./litmus-x64 -c 192.168.1.100 --bidir -b 1G

# UDP with DSCP marking

./litmus-x64 -c 192.168.1.100 --udp -S 46 -l 1400

# Transfer 500 MB then stop

./litmus-x64 -c 192.168.1.100 -n 500M

# JSON output for scripting

./litmus-x64 -c 192.168.1.100 -t 30 -J

# Full certification with PDF report

./litmus-x64 -c 192.168.1.100 --certify

CLI Flag Reference

Mode

-s, --serverRun as server
-c, --client <host>Run as client, connecting to host
--chatRun as chat relay (multicast bridge)

Protocol & Direction

--tcpTCP mode (default)
--udpUDP mode
--bothRun TCP then UDP sequentially
--uploadClient sends, server receives
-R, --downloadServer sends, client receives (default)
--bidirSimultaneous upload and download

Test Parameters

-t, --time <sec>Duration in seconds (default 30)
-n, --bytes <n>Stop after n bytes (e.g. 100M, 1G)
-k, --packets <n>Stop after n packets (UDP)
-P, --parallel <n>Parallel streams, 1–8 (default 1)
-b, --bandwidth <rate>Target bandwidth (e.g. 100M, 1G). 0 = unlimited
-l, --length <bytes>UDP packet size in bytes (default 1400)
-O, --omit <sec>Omit first N seconds as warmup (default 2)

Network & QoS

-p, --port <port>Server port (default 7201)
-B, --bind <iface>Bind to specific local interface
-S, --dscp <n>Set DSCP/QoS value, 0–63
-D, --dont-fragmentSet DF bit (UDP only)
--buffer <KB>Socket buffer size in KB (0 = OS default)
--ramp-up <ms>UDP ramp-up period in ms (default 150)
--pattern <type>Data pattern: random, zeros, ones, alt55, altaa, incrementing, microwave, highbit, custom:0xNN
--port-range <range>Data port range for server (e.g. 10000–10100)

Reporting & Output

-J, --jsonOutput results as JSON
--report [path]Generate PDF report
--report-dir <dir>Auto-save PDF report to directory
--certifyRun all 6 test combinations and generate PDF
--no-reportDisable PDF report with --certify
--log <path>Log file path

Thresholds & Display

--latency-threshold <ms>Latency fail threshold (default 100 ms)
--jitter-threshold <ms>Jitter fail threshold (default 10 ms)
--loss-threshold <%>Packet loss fail threshold (default 0.05%)
--plainDisable colours and Unicode art
--no-tuiPlain-text server output (no TUI)
--showShow effective settings and exit

Frequently Asked Questions

Common questions about Litmus, network speed testing, and how it compares to iperf and online speed tests.

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