See what your USB-C cables, ports, and docks are actually doing.
PortScope is a native macOS app for Apple Silicon that reads a USB-C cable's e-marker and Power Delivery identity through public IOKit APIs, shows every port and device on your Mac in plain language, and — with a license — measures the real sustained throughput your cable and drives can carry.
Its whole reason for existing is that three different things get quoted as one number:
- What the cable claims — the spec printed on the e-marker chip.
- What the link negotiated — the rate the two ends actually trained.
- What the Mac measured — the throughput you really get, right now.
A cable can say "40 Gbps," negotiate 10, and deliver 3 because it's plugged into a hub's slow port. PortScope keeps those three claims separate and tells you which one is holding you back.
Most disk benchmarks hand you a burst number and stop. PortScope writes and reads a real file and keeps analyzing the curve:
- See exactly where the speed drops. A sustained run writes until the drive's fast cache fills and the speed settles, then stops on its own (up to a limit you choose). Each drop is marked on the chart with when it happened, how much had been written, and how hot the drive was.
- SLC write-cache sizing. Consumer SSDs absorb writes into a fast pseudo-SLC region, then fall off a cliff when it fills. PortScope finds that fold-over and reports roughly how big your drive's fast cache is and the slower speed underneath it.
- Thermal throttle detection. It catches the moment a drive slows because it's heating up — and tells that apart from the cache cliff, so you know whether the slowdown is a full cache or a hot controller.
- A verdict that names the bottleneck. The result is judged against the slowest part of the chain: "about 99% of what a 40 Gbps link delivers", or "the drive is the limit, not the cable".
- Honest numbers. Quick tests are labelled burst, only sustained runs are called sustained, and a run is flagged if something else was using the drive or the Mac was holding itself back. On fast NVMe drives the results match AmorphousDiskMark's queue-depth-8 figures.
That's the analysis a tool like Blackmagic Disk Speed Test doesn't give you: not just "how fast," but how long it stays fast, and why it stops. Every run is saved to Speed Test History with its curves, and exports as a PDF report or CSV.
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| Results. Cache size, speed against temperature, and a verdict that names the bottleneck. | Speed Test History. Every run saved with its curves; tick tests to export a PDF report or CSV. |
The only honest way to measure a Thunderbolt or USB4 cable's real ceiling is to take the disk out of the equation. PortScope streams data memory-to-memory between two Macs over the cable under test, so on a Thunderbolt port the cable is the only thing that can be the bottleneck — no SSD, no filesystem, no enclosure limiting the result. Run it on the cable you think is 40 Gbps and find out what it actually carries.
Grab the latest signed release from the Releases page, drag PortScope to Applications, and open it. It's a standard Developer ID–signed, notarized app — no extra tools, no build step.
Buy or manage a license at software.fainimade.com.
- Apple Silicon Mac (M1 or later)
- macOS 15 (Sequoia) or newer
Intel Macs are not supported: their Thunderbolt controllers don't expose cable identity or PD state through any public API.
Everything PortScope reads and inspects is free, forever. The paid tier adds the tools that actively test a cable and a drive, and track them over time.
- Cable identity. Decode the e-marker/PD VDOs (SOP/SOP′/SOP″): passive vs. active, per-lane speed, maximum current and voltage, vendor and cable ID.
- Port inventory. Every physical port — USB-C, HDMI, SD, MagSafe, Ethernet, headphone — with the link each one negotiated (USB 3.x gen, USB4/Thunderbolt tunnel at 20/40/80 Gbps, DisplayPort alt-mode).
- Device topology. A clean "what's actually plugged in" view that folds a dock's many internal hubs into one row, or a full detailed chain if you want it. Devices are classified by their real USB class codes, not product names.
- Live data monitor. Per-device read/write throughput for drives, live network bytes for adapters, and DisplayPort lane allocation — all passive, no test required.
- Power, four ways. Adapter rating vs. cable ceiling vs. negotiated PD contract vs. live draw, never conflated, plus each device's requested USB current budget.
- "Why is this slow?" A one-sentence bottleneck verdict that ranks the real causes and names only the binding one — including the dock-slow-port case nothing else catches.
- Dock bandwidth budget. How a port's link splits between video and data, and whether video is stealing from your data lanes or riding its own.
- Raw data. USB device/interface descriptors and full EDID 1.4 decode with hex dump, for when you need the ground truth.
- Reference library. USB and Thunderbolt speed tiers (with every marketing rename the same rate has been sold under), the full USB-PD power ladder from 5 W to 240 W, and a plain-language glossary — with the rows matching your live hardware badged.
- Menu bar quick view. A live tree of everything connected, grouped by hub, with power, throughput, and volume names at a glance.
- Volumes & drive health. Mounted volumes, free space, drive temperature and NVMe health for internal and Thunderbolt/USB4 NVMe drives.
- Notifications (off by default). Optional system alerts, with a switch for each kind: a device or display connecting or leaving, cable warnings and link errors, a power adapter plugged in or removed, an adapter too weak to charge, a drive running hot, and a finished test.
- Shareable report. A one-page Markdown diagnostic, with personal details redacted by default, ready to paste into a support thread.
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| Docks and bandwidth. How a dock's link is shared between video and data, and everything plugged into it. | Power contract. Adapter rating, cable ceiling, negotiated contract and live draw, kept apart. |
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| Displays. DisplayPort lane allocation, the active signal, and the monitor's EDID identity. | Menu bar. Connected devices with live data and power, a click away. |
- Speed Test. Write then read a real file: quick burst tests, or sustained runs that stop on their own once the cache has filled and the speed settled. A live curve marks each drop with its time, data written and drive temperature, plus SLC write-cache sizing, thermal-throttle detection, a verdict that names the slowest link, and Speed Test History with PDF and CSV export. (See Highlights.)
- Cable Tester (two-Mac). Stream data memory-to-memory between two Macs over the cable under test, so on a Thunderbolt port the cable is the only thing that can be the bottleneck. Requires a license on both Macs. (See Highlights.)
- Cable Health over time. Track each cable's link-error counters across sessions, so a cable that's slowly degrading shows itself before it strands you mid-shoot.
- Wiggle Test. Flex the cable at each end and along its length while PortScope samples link-error counters at 5 Hz, catching an intermittent fault the instant it glitches — and localizing it to a connector.
- Rename Display. Give a monitor your own name, keyed to its EDID so it sticks across replugs, without ever writing to the display.
A single PortScope license:
- Activates on up to two Macs at once.
- Covers one full major version, for life — buy during 1.x and every 1.x update is yours forever, with no subscription and no expiry.
- Lets you deactivate a Mac from Settings any time, freeing that seat so you can license a different machine (the two-install cap always applies).
A future 2.0 is a separate, optional upgrade — 1.x keeps working regardless.
Activation is a lightweight online check with a 14-day offline grace period, so a flaky connection or an off-grid location never locks you out mid-job.
PortScope runs entirely on your Mac. It reads the system's own IORegistry and hardware telemetry, and nothing about your cables, drives, or machine leaves the device — the only network calls it ever makes are the license check and an optional check for app updates. The diagnostic report is a local file you choose to share, with identifying details redacted by default.
- Changelog — what changed in each release
- License Agreement — the terms your license is granted under
- Privacy Policy — what stays on your Mac, and the two times the app goes online
- Acknowledgments — third-party notices
This repository hosts PortScope's releases and documentation. The application's source code is not public.
© 2026 Faini Made Inc. All rights reserved. PortScope is a companion to a continuity tester, not a replacement — it verifies identity and throughput, not pin-level wiring.