Grand Perspective and Disk Inventory X are two of the oldest Mac storage tools still in active use, both open source, both free, and both still capable of answering the basic question — where did my disk space go — reasonably well two decades after their first release. If they still work, the natural question is what a paid alternative is actually buying you.
What the open-source classics do well
Grand Perspective, first released in 2005, established the treemap-as-Mac-storage-tool pattern that most later tools, paid and free, have followed in some form. It scans a folder or volume and draws a proportional map of nested rectangles, colour-coded by file type. Disk Inventory X, from a similar era, does a comparable job with its own visual style, including a similar treemap plus a supplementary sunburst-style view.
Both are free, both are open source (meaning their source code is publicly auditable — a real privacy advantage, since you don't have to take a vendor's word for what the app does; you or anyone else can read the code), and both have been stable for a long time. For a straightforward "show me a map of this folder" task, they remain functional tools, and their longevity is itself a point in their favour: a piece of software that's been maintained or at least kept working for twenty years has survived a lot of macOS changes.
Where the classics show their age
Being from 2005 also means these tools predate a lot of what's changed about how Macs are used and what fills their disks. Development caches with the specific structure of modern node_modules trees, Xcode's DerivedData, and Docker's VM disk images did not exist as categories when these tools were designed, so there's no built-in recognition of what these folders represent — you see a large folder named DerivedData and have to already know what it is.
APFS, the filesystem macOS has used since 2017, introduced concepts like fast directory sizing, copy-on-write cloning, and space-sharing between snapshots that didn't exist under the older HFS+ filesystem these tools were originally built against. A tool that hasn't been substantially updated for APFS-era concepts may not account for space-sharing behaviour accurately, which can produce numbers that look correct on the surface but don't reconcile the way you'd expect against df -h.
Interface conventions have also moved on. Neither tool has been substantially redesigned for modern macOS visual conventions, which isn't a functional problem but is a real one for anyone who finds a dated interface harder to read quickly.
What a paid tool is generally buying you
Setting aside any specific vendor, the categories of value a paid Mac storage tool typically offers over a free classic are:
- Folder recognition and explanation — automatically identifying that a given folder is a Docker VM disk, an Xcode simulator device, or a specific package manager's cache, and explaining what it's for and whether it's safe to remove, rather than requiring you to already know.
- Active maintenance against current macOS versions — keeping pace with sandboxing changes, permission model updates, and new filesystem behaviour as Apple ships them.
- A more integrated cleanup workflow — some paid tools build cleanup review and safety checks directly into the scanning experience, rather than leaving you to act on what you found using Finder separately.
- Support — someone to ask when something doesn't work, which an unmaintained open-source project may not reliably offer.
None of these are guaranteed by paying money — a paid tool can be poorly maintained, and a free tool can be excellent. The categories above are what the payment is for, not a guarantee of quality, which still has to be evaluated tool by tool using the same criteria (privacy, cleanup safety, permission handling) covered elsewhere in this series.
The honest tradeoff
| Open-source classics | Paid tools generally | |
|---|---|---|
| Cost | Free | One-time or subscription |
| Source auditable | Yes | Rarely |
| Folder-type recognition | Minimal or none | Often a headline feature |
| Active maintenance | Varies, often minimal | Varies, but incentivised by payment |
| Interface currency | Dated | Usually current |
The honest way to frame the decision isn't "paid is better" or "free is better" — it's that a free, unmaintained, source-auditable tool and a paid, actively maintained, opaque tool are solving overlapping but not identical problems, and which one is worth it depends on whether you value the explanation layer enough to pay for it, and whether you're comfortable with either the maintenance risk of the free option or the opacity of the paid one.
Auditability is a real property, not a slogan
It's worth dwelling on what "open source" actually buys you beyond price, because it's frequently mentioned but rarely explained. When an application's source code is published, anyone with the relevant skill can read exactly what it does — including whether it makes network connections, what it does during a cleanup operation, and how it calculates the numbers it shows you. This doesn't mean every user personally reads the code, but it means someone could, and often has, and issues get reported publicly rather than staying invisible.
A closed-source tool, paid or free, asks you to trust the vendor's own description of its behaviour, verified only by the kind of external testing covered elsewhere in this series — network monitoring, comparing totals against du, and so on. That's a real form of verification, but it's inherently more limited than being able to read the actual logic. Neither path is disqualifying on its own; it's simply a different amount of trust being asked of you, and worth weighing alongside everything else a tool needs to get right.
Maintenance risk is a two-way street
It's tempting to assume open-source tools carry more maintenance risk than paid ones, since there's no direct revenue tied to keeping them updated. In practice this isn't a clean rule either way — some open-source projects are maintained for decades by dedicated volunteers or small communities, while some paid products get discontinued when a vendor moves on to something else, or get acquired and deprioritised. The honest signal to look for, regardless of licensing model, is a visible changelog or release history showing the tool has actually been updated against recent macOS versions — not just an assumption based on whether money changes hands.
A reasonable way to decide
If your need is occasional and you're comfortable interpreting an unlabelled folder name yourself, a free classic tool costs nothing and still works. If you find yourself repeatedly looking up what a folder like ~/Library/Developer/CoreSimulator/Devices actually is, every time you use a storage tool, that's a concrete signal that the explanation layer a paid tool offers has real value for your specific workflow — not a hypothetical one.
Where VolumeLens fits
VolumeLens is a paid-and-free hybrid rather than purely one or the other: scanning, browsing, search, and cleanup are free and don't expire. The paid Insights tier adds automatic recognition of the two dozen most common storage sinks on a developer's Mac — including Docker's VM disk, Xcode's DerivedData and simulators, and the caches for most major package managers — plus CSV export. It's a one-time payment covering up to three Macs, not a subscription. You can try the free tier first and decide for yourself whether the explanation layer is worth paying for — see pricing for the specifics, or download it to start with the free scan.