The short answer. xScope is the toolset: rulers, guides, a loupe, a dimension overlay and colour inspection in one app, which is why it has survived so long. Mark Man measures and specs — distances, sizes and annotations that can be handed to a developer. Screen Loupe is the open-source magnifier that shows any part of the screen pixel-true in a separate window. Free Ruler is the on-screen ruler, and Loupe is the accessibility inspector that produces output an agent can read. The dividing question is whether you are measuring something on screen or specifying something for someone else, because a ruler answers a question for you and a spec answers it for a developer.
This guide covers 5 measurement tools for designers on mac for macOS. Every fact below is drawn from the same verified records that back each app’s own page. The recommendations are our editorial judgment, not payment.
Quick comparison
| App | What it is | Pricing | Licence | Version |
|---|---|---|---|---|
| Free Ruler | system tool | Open source | MIT | 2.0.19 |
| Loupe | developer tool | Open source | MIT | 1.1.1 |
| Mark Man | design tool | not published | not published | — |
| Screen Loupe | design tool | Open source | MIT | 1.4.0 |
| xScope | Mac utility | not published | not published | 4.7.2 |
What actually decides this
- Measure or specify. A ruler, a loupe and a dimension overlay are for your own eyes. A spec with annotations is a document for someone else. The second needs export and labelling, which is a different feature set from a live overlay.
- Whether it measures the screen or the image. Screen pixels and image pixels are the same thing only at 1x. On a Retina display a measurement taken from a screenshot needs to know the scale, and a tool that reports the wrong unit is worse than no tool.
- What the magnifier actually shows. A pixel-true zoom is a measurement instrument. A smoothed zoom is a preview. For checking an alignment or a colour, only the first is useful.
- Whether the overlay can stay on top. A measurement that disappears when you click the window is a measurement you take twice. A floating overlay that survives app switching is the difference between a tool and a demo.
- What it produces for accessibility work. Inspecting a control’s role, label and frame is a different job from measuring a gap, and it is the one that produces a report someone can act on. Tools that generate structured output are doing the newer work in this category.
Our picks
- xScope — Its record describes a toolset for measuring, inspecting and testing on-screen layouts and graphics, which is the toolset case. Choose it when you want rulers, guides, a loupe and colour in one toolset.
- Mark Man — Its record describes measuring and specifying quickly, which is the spec case. Choose it when the measurements have to be handed to a developer.
- Screen Loupe — Its record describes a live magnifier showing any part of the screen zoomed pixel-true, which is the magnification case. Choose it when you need a pixel-true magnifier in its own window.
- Free Ruler — Its record describes a ruler for the Mac, which is the minimal case. Choose it when you want a ruler on the screen and nothing else.
- Loupe — Its record describes an accessibility inspector that generates agent-ready output, which is the inspection case. Choose it when the job is accessibility inspection rather than distance.
The apps
Free Ruler
Free Ruler is a system tool for macOS. A ruler for your Mac. It is released under MIT.
What it does. Multiple rulers, with horizontal and vertical arms. Choose from units: pixels, millimeters, or inches (press U to cycle). Float rulers above other applications (press F to toggle). Move rulers independently or as a group (press G to toggle).
Free Ruler is listed with current version 2.0.19.
Full profile and verified facts for Free Ruler →
Loupe
Loupe is a developer tool for macOS. Accessibility inspector that generates AI-agent-ready output. It is released under MIT.
What it does. macOS accessibility inspector for AI-agent workflows. Hover, annotate, copy structured output.
Loupe is listed with current version 1.1.1.
Full profile and verified facts for Loupe →
Mark Man
Mark Man is a design tool for macOS. Measure & Spec Fast. Its pricing is not published.
Full profile and verified facts for Mark Man →
Screen Loupe
Screen Loupe is a design tool for macOS. Open-source live magnifier that shows any part of the screen zoomed, pixel-true, in a separate window. It is released under MIT.
What it does. Native macOS screen loupe: a floating capture area mirrored live into a zoomable, pixel-sharp viewer.
Screen Loupe is listed with current version 1.4.0.
Full profile and verified facts for Screen Loupe →
xScope
xScope is a Mac utility for macOS. Toolset for measuring, inspecting, and testing on-screen layouts and graphics. Its pricing is not published.
What it does. xScope is a powerful set of tools for Mac OS X that are ideal for measuring, aligning and inspecting on-screen graphics and layouts.
xScope is listed with current version 4.7.2.
Full profile and verified facts for xScope →
How to choose
- No licence fee, source available. Free Ruler, Loupe and Screen Loupe — the source can be read and, under the terms of each licence, reused.
- Pricing not published in our data. Mark Man and xScope — check the developer’s own site before assuming anything about cost.
Open source: Free Ruler, Loupe and Screen Loupe (3 of 5).
Common mistakes
- Measuring on a Retina display and reporting the number as CSS pixels.
- Taking a measurement with a smoothed magnifier and trusting the edge.
- Specifying a layout in a screenshot instead of a document a developer can query.
- Leaving five overlays on screen and losing the one that mattered.
How this guide was put together
Each app’s facts come from its own record: the developer’s own pages and repository, the App Store listing where one exists, and the documentation, each with a source grade and an access date. Where a fact rests on the developer’s own statement rather than on something we verified independently, the sentence says so. Where our data has no value for something, the guide says “not published” instead of guessing.
A price appears here only where the record carries one from a stated source; the guide never estimates one, and it records the pricing model alongside so the two can be read together. Prices change and vary by region, so each app links to its own page for the current detail.
The facts and the recommendations are kept apart on purpose. Everything in the app entries, the comparison table and the answers above is composed from the records. The short answer, the criteria and the picks are our editorial judgment: they reflect what we would choose and why, and they are not paid for. Where we make a recommendation we name the condition it applies under, because we do not call anything “the best” without explaining the criteria.
Frequently Asked Questions
How do I choose between these measurement tools for designers on mac?
There is no single answer — it depends on what you need. This guide covers 5 measurement tools for designers on mac: Free Ruler, Loupe, Mark Man, Screen Loupe and xScope. They differ mainly in pricing model, licence and the trade-offs each one carries. Pick by the trade-off you care about rather than by rank.
Are these measurement tools for designers on mac free?
Pricing across this group: open source (Free Ruler, Loupe and Screen Loupe) and not published (Mark Man and xScope). Where we list pricing as not published, the developer does not state a model we could verify — check their own site before assuming anything about cost. We quote a price only where the record carries one from a stated source, and we never estimate one. Prices change and vary by region and by store, so always check the developer’s own page for the current figure.
Which of these measurement tools for designers on mac are open source?
Free Ruler (MIT), Loupe (MIT) and Screen Loupe (MIT) are open source.
Do these measurement tools for designers on mac support Apple Silicon?
Our data does not carry an explicit Apple Silicon statement for any app in this group, so we do not claim one. The absence of a statement is not the same as the absence of support.
How do I choose between them?
Start with how you pay: the guide groups these apps by pricing model, because the budget is the constraint most people actually have. Then check the trade-offs listed for each app: the limitations are the part that decides most people’s choice, because they describe what the app will not do for you.
