whatcable.uk

WhatCable does not test a cable's physical wires. It reads the identity and capability data that the cable's e-marker chip reports, reads the USB-C and USB Power Delivery details macOS already exposes for the port, and then compares the two against what the Mac actually negotiated. The result is a plain-English explanation of the cable's reported speed and charging rating, with the original readings available on demand. This applies to WhatCable on Apple Silicon Macs running macOS 14 or later.

Where the data comes from

WhatCable combines two sources:

• The cable's reported identity. USB-C cables that carry an e-marker chip declare their speed and charging rating electronically. WhatCable reads that declaration rather than guessing from the cable's appearance.
• The connection as macOS sees it. WhatCable reads the port, cable, charger, adapter and connected device together, because, as the site puts it, "a cable never works alone."

The app then checks the reported identity against USB Power Delivery rules and compares it with what the Mac actually negotiated. That comparison is the core of the method: a claim is one thing, observed behaviour is another.

What "speed" and "charging rating" mean in the app

The site's own examples show this format: a CalDigit TB5 cable reported as USB4 80 Gbps, 240W, passive; an Anker 333 nylon cable as USB 2.0, 100W, passive.

How it explains slow charging

For a slow-charging question, WhatCable shows what the charger offers, what the cable supports, and whether the Mac is drawing the power it needs, then explains the result. The site gives a concrete example of the output: "Charger and cable are fine. The Mac will draw up to 94W when it needs to." That tells you the limit is not the cable or charger, so swapping components at random is unnecessary.

What it cannot tell you

WhatCable reads what a cable reports and what the Mac negotiates. It cannot see inside the cable jacket and, per the site, "never pretends it can." So a cable that misreports its identity will be shown as reporting that identity; the app surfaces the discrepancy between claim and negotiated behaviour rather than physically verifying the wires. Treat the readings as evidence about identity and negotiation, not as a lab measurement of the cable.

Checking a cable against the public record

WhatCable also maintains a public database of cable observations contributed by users, reported through the app. At the time of the site's description it held 145 cable observations, searchable by vendor, speed and identity. Nothing is uploaded without your action. If you want to see whether your cable has appeared before, browse the database by vendor, speed or identity before drawing conclusions from a single reading.

Free vs Pro, as described

The free version covers understanding the current connection. Pro is for inspecting the evidence, watching measurements and investigating changes over time. The app is open source with Pro optional, signed and notarised, and available in 19 languages. The site does not state Pro pricing on the pages summarised here, so check the Pro page for current terms.

WhatCable is a free macOS menu bar app for Apple Silicon Macs (macOS 14+) that reads your USB-C port, cable, charger, adapter, and connected device together, then explains in plain English why your Mac may be charging slowly. It shows what the charger offers, what the cable supports, and whether the Mac is drawing the power it needs — so you can stop swapping cables and chargers at random. It works on the free tier for understanding the current connection; deeper inspection of evidence and measurements over time is part of WhatCable Pro.

What the app actually checks

A USB-C cable never works alone. Slow charging can come from the charger, the cable, the adapter, or the Mac's own power draw. WhatCable reads the whole chain rather than one link:

• Charger output — what wattage the charger reports offering.
• Cable rating — the cable's reported identity, speed, and charging rating, including what its e-marker chip claims.
• Negotiated power — what the Mac and charger actually agreed on under USB Power Delivery rules.
• Actual draw — whether the Mac is pulling all the power available to it.

The app then states the result in plain English, for example that the charger and cable are fine and the Mac will draw up to 94W when it needs to — meaning the slow charging is expected behaviour, not a fault.

How it reaches its conclusion

WhatCable reads the identity a cable reports, checks it against USB Power Delivery rules, and compares that with what the Mac actually negotiated. It is explicit about its limits: it cannot see inside the cable jacket and does not pretend to. That distinction matters — a cable's claim and its observed behaviour are different things, and the app shows both.

You can open the technical details to see the original readings if you want to verify the plain-English summary yourself.

A practical way to use it

1. Connect the charger and cable you suspect, with the Mac awake.
2. Open WhatCable from the menu bar and read the charging summary.
3. Note which component the app identifies as the limit — charger, cable, or expected Mac behaviour.
4. Swap only that component and re-check, rather than changing everything at once.

Expected result: you either find the bottleneck (for example, a cable rated below what the charger offers) or confirm the setup is working as intended.

Common sticking point: a cable that reports a high rating but behaves below it. WhatCable's comparison of claimed identity against negotiated power is designed to surface exactly this kind of mismatch.

Beyond your own cable

WhatCable also maintains a public database of cable observations contributed by users — 145 at the time of the site's description — searchable by vendor, speed, and identity. Nothing is uploaded without your action. If you are shopping for or troubleshooting a specific cable, you can check whether it has appeared before. The same diagnostic engine is also available in your terminal if you prefer that workflow.

When it helps — and when it won't

It helps when you have a slow-charging Mac and want a specific answer instead of guesswork. It won't tell you anything about a cable's internal construction, and it depends on what the hardware and macOS expose. For pricing details on Pro and installation options, including Homebrew, see whatcable.uk directly.

The WhatCable public cable observation database is a searchable record of how real USB-C cables identify themselves across real hardware, built from observations that WhatCable users choose to contribute. You can search it by vendor, speed, and identity, or check whether a cable you own has already appeared. It is useful when you want to compare a cable's reported identity against what other people's hardware has seen, rather than relying on marketing claims alone. Nothing is uploaded without your action.

What the database contains

Each entry records what a cable reported about itself when connected through WhatCable — its identity, speed, and charging rating — as observed on real machines. The site describes the collection as "a public record of how real cables identify themselves across real hardware," and at the time of writing lists 145 cable observations.

Example entries shown on the site include:

These illustrate the kind of mismatch the database can surface: cables that look identical can report very different capabilities.

How observations get there

The flow is deliberately manual:

1. You connect a cable (and typically a device or charger) and let WhatCable read the connection.
2. WhatCable reads the identity the cable reports, checks it against USB Power Delivery rules, and compares it with what the Mac actually negotiated.
3. If you choose to contribute, the observation is submitted. According to the site, nothing is uploaded without your action.

WhatCable cannot see inside the cable jacket, and the site states it never pretends to — the database reflects reported identity and observed negotiation, not physical inspection.

What it helps you decide

• Before buying or trusting a cable: search by vendor or speed to see whether your model has been observed and what it reported.
• When a cable underperforms: compare your cable's reported identity with other observations of the same model to judge whether the limit is the cable, the charger, or the device.
• When claims and behaviour diverge: the database is a cross-check against spec sheets, since entries come from real hardware rather than vendor documentation.

Limits to keep in mind

The database is only as complete as user contributions — a cable that hasn't appeared may simply not have been observed yet, not be suspect. Entries describe reported identity and negotiated behaviour, which can differ from a cable's true internal construction. And because submission requires your action, your own observations stay local unless you choose to share them.

To browse entries, use the cable database linked from whatcable.uk; the app itself is a free Mac download for Apple Silicon running macOS 14 or later, with an optional Pro tier for deeper inspection.

The free version of WhatCable explains the connection you have right now; WhatCable Pro adds the ability to inspect the evidence behind that explanation, watch measurements over time, and investigate changes. Both run the same diagnostic engine, the app is open source, and Pro is optional — so the free tier is the right starting point unless you need to dig into why a setup behaves the way it does.

What the free version covers

According to WhatCable's own description, the free tier is for "understanding the current connection." In practice that means:

• Charging diagnosis — see what the charger offers, what the cable supports, and whether the Mac is drawing the power it needs. The app explains the result rather than leaving you to swap parts at random.
• Cable identity — the cable's reported identity, speed and charging rating, plus the kind of connection in use.
• Whole-connection view — it reads the port, cable, charger, adapter and connected device together, then states the outcome in plain English.
• Technical details on demand — the original readings are available when you want them.

That set answers the common questions the app is built around: why a Mac is charging slowly, what a given USB-C cable can actually do, and what may be limiting a display connection.

What Pro adds

The site describes Pro as the tier to "inspect the evidence, watch measurements and investigate changes over time." Three additions follow from that wording:

The distinction is scope, not accuracy: free tells you what is happening and why, Pro lets you follow it as conditions change — for example, when a charger, cable or dock is swapped and you want to see what shifted.

How WhatCable reaches its answers

The method matters for judging whether the free explanation is enough. WhatCable reads the identity a cable reports, checks it against USB Power Delivery rules, and compares that with what the Mac actually negotiated. The site is explicit that it cannot see inside the cable jacket and does not claim to. So the output is a reading of reported identity plus observed negotiation — useful for spotting cables whose claims don't add up, but not a physical test of the wire.

A related feature is the public cable database: 145 cable observations at the time of the site text, searchable by vendor, speed and identity, and nothing is uploaded without your action. Browsing it can tell you whether your cable has been reported before — a check that works without Pro.

Requirements and availability

• Apple Silicon Mac, macOS 14 or later
• Signed and notarised
• Available in 19 languages
• Free download, with a Homebrew install option
• Open source, with Pro as an optional paid tier (a "Get Pro" link exists on the site; the page text does not state a price)

Which one you need

Choose free if your question is "why is this charging slowly?" or "what can this cable do?" and you want an answer for the setup in front of you. Choose Pro if you are comparing components, troubleshooting an intermittent problem, or want a record of how measurements change as you swap hardware. Because both share the diagnostic engine, starting free and upgrading only when you hit the limits of a single-snapshot explanation is the lower-risk path.

WhatCable is a macOS menu bar app that diagnoses USB-C connections. You connect a device or charger, and it reads the port, cable, charger, adapter, and connected device together, then explains in plain English what the cable can do and what may be limiting your setup. It is free to download, open source, and built for Apple Silicon Macs running macOS 14 or later. A paid Pro tier exists for deeper inspection, but the free version covers understanding your current connection.

What it tells you

The app answers three practical questions that are hard to resolve when every USB-C cable looks identical:

• Charging: Why is this Mac charging slowly? WhatCable shows what the charger offers, what the cable supports, and whether the Mac is drawing the power it needs. For example, it might report that the charger and cable are both fine and the Mac will draw up to 94W when it needs to — so the bottleneck is elsewhere.
• Cable identity: What kind of cable is this? It shows the cable's reported identity, speed rating, and charging rating, plus the kind of connection in use. You can open the technical details to see the original readings.
• Display connection: It explains what your display connection is doing and what may be limiting it.

How it reaches its answers

WhatCable reads the USB-C and USB Power Delivery details macOS already exposes. It checks the identity a cable reports against USB Power Delivery rules and compares that with what the Mac actually negotiated. The site is explicit about the limit: it cannot see inside the cable jacket and does not claim to. So the output is "reported identity plus observed behaviour," not a physical teardown.

That distinction matters. A cable can claim a rating that the actual negotiation doesn't match — the site's framing is "spot cables that don't add up." If a cable reports 240W but the Mac negotiates far less, the app surfaces the mismatch rather than leaving you to swap components at random.

Free vs. Pro

The free tier is enough to answer "why is my Mac charging slowly?" or "what is this cable?" Pro is aimed at people who want to track behaviour across sessions or dig into the raw evidence. The site does not publish Pro pricing on the pages reviewed, so check the Pro page before assuming a cost.

Other things to know

• Install options: Download directly, or install via Homebrew if you prefer.
• Trust signals: Open source, signed and notarised, available in 19 languages.
• Terminal version: The same diagnostic engine is available in your terminal if you work on the command line.
• Cable database: Users can optionally contribute observations to a public database of how real cables identify themselves — 145 cable observations at the time of the site content, searchable by vendor, speed, and identity. Nothing is uploaded without your action, so you can check whether your cable has already appeared before contributing.

Who it's for

If you own a modern Mac and a drawer of indistinguishable USB-C cables, WhatCable replaces guesswork with a readout: which cable is limiting your charge speed, whether your display link is running at the expected standard, and what a cable actually reports about itself. If you need hardware-level verification of a cable's internals, this isn't that tool — and the site says so plainly.