iperf3

iperf3 is an active network throughput testing CLI that runs as either a client or a server to measure TCP, UDP, or SCTP path performance between two hosts. It is built for bandwidth and transport diagnostics, not passive monitoring.

• Measure upload or download throughput, transfer rates, retransmits, loss, and jitter between a client and a reachable iperf3 server.
• Run repeatable TCP, UDP, or SCTP tests with control over duration, bitrate, parallel streams, buffer sizes, reverse mode, and one-off server behavior.
• Capture client-side and server-side test results for incident response, capacity checks, network tuning, or post-change verification.

• The CLI is non-interactive and flag-driven, so it works cleanly in scripts, CI checks, and inspect or verify loops.
• Real machine-readable output exists: -J emits a full JSON result object, and --json-stream can emit line-delimited JSON during long tests.
• Best fit for agents that already control both ends of a path or can target an existing test server; it measures network performance but does not discover or fix the underlying cause.

• You need an iperf3 server or another managed endpoint on the far side; it is not a passive local-only inspection tool.
• iperf3 is not backward compatible with iperf2, so both ends need the iperf3 protocol.